COVID-19 (SARS-CoV-2)

Meet the patient

A 62-year-old man with type-2 diabetes and a BMI of 33 arrives on day 6 of a flu-like illness. He is chatting on his phone, his chest is clear to auscultation, and the junior wants to discharge him with paracetamol. The triage pulse oximeter reads SpO2 84% on room air — and he is not even breathless.[1]

That single number is why this is the most dangerous hour of his life. The whole topic hangs on two questions you must ask of every COVID-19 stem: is the patient hypoxaemic? and is the trajectory rising or flat? Answer those two and the therapy ladder, the steroid rule, the heparin rule and the cytokine-phase trap all fall into line.[2]

One virus, one receptor, five faces

COVID-19 is the clinical illness caused by SARS-CoV-2 — an enveloped, positive-sense, single-stranded RNA betacoronavirus of the subgenus Sarbecovirus that emerged in Wuhan in late 2019 and was declared a WHO pandemic on 11 March 2020.[1]

Name-drop for viva gold: corona is Latin for "crown" — the spike proteins electron-microscope into a halo around the virion. SARS-CoV-2 is the third coronavirus to jump to humans in two decades, after SARS-CoV (2002) and MERS-CoV (2012).[1]

The spectrum runs far wider than any cold, and every tier drives a different management decision:[1]

• Asymptomatic and pre-symptomatic infection — viral RNA detectable with no symptoms; the stealth driver of spread, because people transmit before they feel ill and without ever feeling ill.[8]
• Mild illness — fever, cough, sore throat, fatigue, myalgia, anosmia; no hypoxaemia, no radiographic pneumonia.
• Moderate illness — clinical or radiographic pneumonia with SpO2 at least 92% on room air.
• Severe illness — pneumonia with SpO2 under 92% on room air, RR over 30, or infiltrates across more than 50% of lung fields.
• Critical illness — ARDS, sepsis or septic shock, or multi-organ failure demanding intensive care.[1][2]

Two post-infectious syndromes belong to the definition, not a footnote, because examiners test both:[1]

• Multisystem inflammatory syndrome (MIS) — MIS-C in children, MIS-A in adults — persistent fever with multi-organ involvement and shock, 2 to 6 weeks after SARS-CoV-2 infection.
• Post-COVID condition ("long COVID") — WHO: symptoms developing within 3 months of onset, lasting at least 2 months, not explained by another diagnosis.[1]

Everyone forgets: the clinical skill in COVID-19 is not making the diagnosis (PCR or antigen does that) — it is reading the severity and the trajectory, picking the right rung of the therapy ladder, preventing thromboembolism, and anticipating the sequelae. The virus is easy; the host response is what kills.[1]

The severity ladder — oxygen is the gate

Severity, not diagnosis, decides everything. This is the single table a final-prof candidate must reproduce, because every drug below hangs off the SpO2 column:[1]

[1]

The classic trap: SpO2 under 92% on room air is the gate that swings open the dexamethasone door. Above 92%, steroid is harm, not help.[3]

By viral lineage — the variants of concern (VOC), an examiner perennial. The face-off that earns marks is which mutation does what:[1]

[1]

The one-line discriminator: N501Y means more transmissible; E484K or K417N or K417T means immune evasion. Delta (India 2021) was both more transmissible and more severe; Omicron dodges immunity but prefers the upper airway, so it is generally milder per case yet catastrophic by sheer numbers.[1]

The ARDS-phenotype wrinkle (advanced, but viva gold): Gattinoni split COVID lungs into Type-L ("Low") — low elastance, surprisingly compliant, often the "happy hypoxaemic" early lung — and Type-H ("High") — high elastance, high D-dimer, the dense classic ARDS of later severe disease. The lesson that bites: high PEEP can worsen a Type-L lung by overdistension, so PEEP is individualised, not cranked up reflexively.[1]

How common, who dies, and why

COVID-19 racked up over 770 million confirmed cases and over 7 million reported deaths by 2024 — and true excess-mortality estimates run two to three times higher. Successive waves rode variants and population immunity, with Omicron sublineages dominant from late 2021 on.[1]

Modes of transmission — and the one that matters most has changed:[1]

• Respiratory droplet (over 5 micrometres, short range under 1 m) — the classical route.
• Aerosol (under 5 micrometres, travels further and lingers) — now recognised as the dominant mode, especially in closed, crowded, poorly ventilated indoor spaces; the basis for airborne-precaution PPE and ventilation.
• Contact and fomite — a minor route.[1]

The 3 C's to avoid (transmission-risk settings): Crowded places, Close-contact settings, Confined and enclosed spaces.[1]

Key parameters to quote in a viva:[1]

• Incubation — mean 5 days (range 2 to 14); Omicron shorter, about 3 to 4 days.
• Infectious period — from about 2 days before symptom onset (peak infectiousness) to 7 to 10 days after; the immunocompromised may shed for weeks.
• R0 — ancestral 2.5 to 3.5; Omicron's effective reproduction number far higher, around 7 to 10 in susceptible populations.[1]

[1]

Risk factors for severe disease and death — the global signal is remarkably consistent, and age dwarfs everything else:[2]

• Age 65 and over — by far the strongest; mortality rises exponentially with age.
• Comorbidities — cardiovascular disease, diabetes, COPD, asthma, chronic kidney disease (especially dialysis), chronic liver disease, cerebrovascular disease.
• Obesity (BMI 30 and over) — independent and prominent in COVID-19 (mechanical, metabolic, pro-inflammatory).
• Immunocompromise — transplant, chemotherapy, advanced HIV (CD4 under 200), high-dose steroids.
• Pregnancy — more ICU admission, mechanical ventilation and preterm birth.
• Smoking, socioeconomic deprivation and ethnic minority status — the last two driven by structural factors: multigenerational households, occupational exposure, healthcare access.[1]

The triphasic mechanism — viral, then host, then clot

Read COVID-19 as three overlapping phases and the whole disease becomes predictable: viral entry and replication, then a dysregulated host inflammatory response, then endothelial-thrombotic injury. Early disease is a viral problem (treat with antivirals); late severe disease is a host problem (treat with immunomodulators and anticoagulation).[1][2]

1. Entry — one spike, one receptor, two scissors. The virion carries four structural proteins — spike (S), envelope (E), membrane (M), nucleocapsid (N) — on a roughly 30 kb genome. The spike cleaves into two subunits that do two different jobs:[1]

• S1 holds the receptor-binding domain that latches onto ACE2 — densely expressed on type-II pneumocytes, nasal goblet and ciliated cells, bronchial epithelium, enterocytes, renal tubules, cardiomyocytes, vascular endothelium and pancreatic islets (the map of the multi-organ disease).
• S2 drives fusion after priming by TMPRSS2 and furin — and the furin-cleaved polybasic S1/S2 site is the feature the original SARS-CoV lacked, which is why SARS-CoV-2 spreads so much more easily.[1]

Fusion releases viral RNA into the cytoplasm; ORF1a and 1b polyproteins are translated; RNA-dependent RNA polymerase (RdRp) replicates the genome; new virions bud and exit. RdRp is the target of remdesivir.[4]

2. The immune response that fails two ways. A brisk early type-I and type-III interferon response usually aborts infection. Severe COVID-19 is defined by the opposite — a delayed, blunted interferon response paired with a runaway inflammatory response: macrophage activation and a storm of IL-6, TNF-alpha, IL-1-beta, IL-12 and MCP-1 plus complement (C5a), with lymphocyte apoptosis producing the signature lymphopenia. This "cytokine storm" is exactly what tocilizumab (IL-6 receptor blockade), baricitinib (JAK1 and JAK2 inhibition) and corticosteroids are built to blunt.[9]

3. Endothelialitis, microthrombi and the hypercoagulable state. ACE2 sits on vascular endothelium, so the virus infects the lining itself; endothelial injury plus complement plus cytokines produces diffuse endothelialitis and in-situ microthrombi, especially in the pulmonary bed. Add immobilisation and critical illness and the D-dimer climbs steeply, with deep-vein thrombosis and pulmonary embolism several-fold more common than in matched non-COVID inpatients. This is the non-negotiable rationale for pharmacological VTE prophylaxis in every hospitalised patient.[2]

4. The renin-angiotensin twist. ACE2 normally converts angiotensin-II into the vasodilatory, anti-inflammatory angiotensin-(1-7). Viral binding and internalisation downregulates ACE2, leaving unopposed angiotensin-II — vasoconstriction, inflammation, oxidative stress, fibrosis — a neat mechanistic explanation for the cardiac, renal and vascular injury.[1]

5. The lung — why they desaturate without feeling breathless. Alveolar macrophages release cytokines; neutrophils and proteinaceous exudate flood the alveoli; diffuse alveolar damage with hyaline membranes follows (exudative early, organising later, fibrotic in survivors). The radiological correlate is the bilateral peripheral ground-glass opacity. Hypoxaemia comes from V/Q mismatch, intrapulmonary shunt and loss of hypoxic pulmonary vasoconstriction — and because the early Type-L lung stays compliant, patients can talk and walk with SpO2 in the 70s: silent or "happy" hypoxaemia.[1]

6. Anosmia — why the nose goes first. SARS-CoV-2 infects the sustentacular supporting cells of the olfactory epithelium (which express ACE2 and TMPRSS2), not the olfactory neurons themselves; loss of support starves the receptors. This is why smell usually returns as the epithelium regenerates.[1]

The consultant confession: the day-7-to-10 deterioration you see on the ward is almost never fresh viral replication — it is the host inflammation catching fire. That is why the antiviral window closes around day 10 while the immunomodulator window opens.[9]

The presentation — and the silent one that kills

Incubation 2 to 14 days, mean about 5 (Omicron shorter). Presentation bends to age, comorbidity, vaccination and lineage.[1]

Typical mild-to-moderate COVID-19 reads like influenza at first:[1]

• Fever (often high, with rigors) — but afebrile in 10 to 20% and in the elderly.
• Cough — usually dry at first, may turn productive later.
• Sore throat, coryza, headache, myalgia, fatigue.
• Anosmia and ageusia — the discriminating feature, present in 40 to 60% of symptomatic patients and often preceding respiratory symptoms.
• Diarrhoea and other GI symptoms in 10 to 20%.[1]

Severe COVID-19 — pneumonia tipping into ARDS:[1]

• Dyspnoea is the symptom that usually triggers admission; tachypnoea (RR over 30), accessory-muscle use.
• Hypoxaemia (SpO2 under 92% on room air), classically silent — cyanosis and a low saturation with surprisingly little breathlessness.
• Auscultation may be deceptively quiet despite striking CT changes; bilateral fine crackles come later.
• Rapidly progressive bilateral pneumonia over 24 to 72 hours, with a cytokine-release phase around days 7 to 10 — often after initial improvement.[1]

Critical COVID-19 — ARDS, shock, multi-organ failure:[1]

• ARDS (Berlin definition, in Investigations).
• Septic shock — vasopressor-requiring hypotension with raised lactate.
• Acute kidney injury, often needing renal replacement therapy.
• Cardiac — myocardial injury, myocarditis, new arrhythmia (including atrial fibrillation), Takotsubo-like cardiomyopathy, acute coronary syndrome.
• Neurological — encephalopathy, stroke (large-vessel and microvascular), Guillain-Barre syndrome, seizures.
• Thrombotic — pulmonary embolism, DVT, MI, ischaemic stroke, unusual-site thromboses.
• Dermatological — chilblain-like "COVID toes", urticarial, maculopapular, livedoid rash.[1]

Atypical presentations — the ones that bite:[1]

• Elderly — delirium, falls, reduced mobility, anorexia, drowsiness; fever and cough may be absent. Lower threshold to test, image and admit.
• Diabetic — may present in diabetic ketoacidosis as the first sign of COVID-19.
• Pregnant — risk of severe pneumonia and preterm birth; may present with reduced fetal movements.
• Immunocompromised — silently progressive hypoxaemia, prolonged shedding, sparse symptoms, and the substrate for variant emergence.
• Children — mostly mild or asymptomatic; croup- or bronchiolitis-like; Omicron produces more upper-airway disease. MIS-C is the principal severe paediatric phenotype.[1]

Multisystem inflammatory syndrome in children (MIS-C) is the paediatric emergency: persistent fever (3 or more days) plus multi-organ involvement — rash, conjunctivitis, mucosal change, abdominal pain, vomiting, myocarditis with shock, coronary-artery aneurysm, AKI, hepatitis, neurological features — 2 to 6 weeks after SARS-CoV-2 infection, often with serological evidence of recent infection and a negative PCR. It overlaps Kawasaki disease but skews older, with more GI, more cardiac, prominent shock and thrombocytopenia.[1]

What else it could be

A febrile illness with respiratory or radiographic findings in the COVID era is not always COVID-19. The discriminator column is where the marks are:[1]

• Influenza pneumonia — similar dry cough, fever, myalgia; more abrupt onset, seasonal epidemiology; rapid antigen or PCR positive for influenza; CT more central and peribronchovascular.
• Bacterial CAP (typical, S. pneumoniae) — abrupt, productive purulent or rust-coloured sputum, lobar consolidation, neutrophilia rather than lymphopenia, rapid beta-lactam response.
• Atypical bacterial pneumonia (Mycoplasma, Chlamydophila, Legionella) — insidious, dry cough, systemic features, patchy interstitial CXR. Legionella adds GI symptoms, confusion, hyponatraemia, raised LFTs, positive urinary antigen.
• Other viral pneumonias (RSV, adenovirus, hMPV, parainfluenza) — distinguish by multiplex respiratory PCR.
• Pulmonary embolism — sudden dyspnoea, pleuritic pain, syncope; CXR often normal; D-dimer raised (also raised in COVID-19, which is the trap); CTPA is definitive. Both can coexist in COVID-19.
• Tuberculosis — subacute or chronic, night sweats, weight loss, upper-lobe cavitation, positive sputum AFB or NAAT.
• Pneumocystis jirovecii pneumonia (HIV or immunocompromised) — subacute dyspnoea, perihilar ground-glass, pneumothorax, raised LDH, low CD4.
• Cardiogenic pulmonary oedema — bilateral alveolar infiltrates, cardiomegaly, raised BNP or NT-proBNP, echocardiographic dysfunction.
• COPD or asthma exacerbation — usually triggered, wheeze prominent, less fever and CRP, bronchodilator response.
• Hypersensitivity pneumonitis, organising pneumonia, drug-induced pneumonitis — exposure or drug history, eosinophilia.[1]

The MIS-C differentials to name on the spot: Kawasaki disease, staphylococcal and streptococcal toxic-shock, bacterial sepsis, juvenile systemic lupus flare, and haemophagocytic lymphohistiocytosis (HLH).[1]

Everyone forgets co-infection. Bacterial superinfection (pneumococcal, staphylococcal, especially post-influenza) and other respiratory viruses ride alongside COVID-19 often enough that a respiratory virus PCR panel belongs in every moderate-to-severe case.[1]

The bedside round — read the trajectory, not just the vitals

Vital signs drive severity and disposition, and one number outweighs the rest. In every suspected case measure:[1]

• SpO2 on room air — the single most important bedside number; measure on room air for at least 5 minutes, then record the response to oxygen. Target 92 to 96% in most adults, 88 to 92% in COPD or type-2 respiratory failure.
• Respiratory rate — the most sensitive single sign of lower-respiratory compromise; RR over 30 is a severe-disease criterion.
• Work of breathing — accessory-muscle use, intercostal recession, inability to speak full sentences.
• Blood pressure, heart rate, temperature, capillary refill, conscious level (GCS or NEWS2).
• Hydration and urine output — AKI is common in severe disease.[1]

Detecting silent hypoxaemia (the pitfall that kills):[1]

• 6-minute walk test in ambulatory patients — a drop in SpO2 of 3 percentage points or more (or to under 92%) is abnormal and warrants admission.
• 1-minute sit-to-stand test — a useful bedside surrogate.[1]

Awake proning is the free bedside manoeuvre that buys oxygenation — it recruits dorsal lung segments, improves V/Q matching, reduces shunt and helps diaphragmatic mechanics:[1]

• Indication — awake, cooperative patient with SpO2 under 92% despite supplemental oxygen, not needing immediate intubation.
• Protocol — prone 2 hours at a time, 3 to 4 sessions daily, building to 12 to 16 hours a day; rotate between prone and lateral.
• Contraindications — spinal instability, recent abdominal or thoracic surgery, 3rd-trimester pregnancy, haemodynamic instability, severe obesity that prevents safe turning, agitation, raised intracranial pressure.[1]

Chest auscultation is often deceptively quiet early despite striking imaging; bilateral fine basal crackles and reduced breath sounds develop as exudate accumulates. A silent hemithorax with dullness points to effusion, collapse or pneumothorax (a recognised COVID complication).[1]

Document a trajectory every day — improving, static, or worsening. A worsening trajectory with rising CRP, ferritin and D-dimer and a falling lymphocyte count is the trigger to reach for tocilizumab or baricitinib and to escalate to ICU.[1]

Confirm the virus, read the storm

Diagnostic tests confirm SARS-CoV-2; the bedside and inflammatory panel reads the host response. Both matter.[1]

• RT-PCR — gold standard. Detects viral RNA in a nasopharyngeal (or combined naso/oropharyngeal) swab, sputum or BAL. Sensitivity peaks days 3 to 7 and falls after day 10, though PCR may stay positive for weeks (non-viable RNA). The cycle threshold (Ct) carries meaning: Ct under 25 indicates high viral load; Ct over 35 typically means non-infectious residual RNA.
• Rapid antigen test (RAT) — faster and cheaper, lower sensitivity early and in asymptomatics; useful for triage and surveillance.
• NAAT, CRISPR-based and molecular point-of-care tests — varying speed and accuracy; RT-PCR remains the standard.
• Serology (anti-S, anti-N antibodies) — confirms prior infection; anti-N distinguishes natural infection from vaccination (vaccines target spike only); not useful for acute diagnosis, as IgM is unreliable.
• Whole-genome sequencing — for variant surveillance.[1]

Chest imaging — the CT pattern is so characteristic it is nearly pathognomonic in the right context:[5]

• Chest X-ray — often normal early; the classic picture is bilateral, peripheral, mid- and lower-zone opacities (ground-glass then consolidation).
• Chest CT — the most sensitive modality. Hallmarks: bilateral, peripheral (subpleural), posterior-basal ground-glass opacities (GGOs); crazy-paving (GGO with interlobular septal thickening) and consolidation; vascular enlargement, the reverse-halo (atoll) sign, and fibrotic bands in the organising phase. Ground-glass opacity is hazy increased attenuation without obscuration of bronchovascular markings (consolidation obscures them).
• Lung ultrasound — bedside B-lines (comet-tail artefacts) in a multifocal, patchy, often spared pattern; useful in resource-limited or infection-control settings.[5]

The lab profile of severe COVID-19 reproduces the inflammatory phenotype — and a rising trajectory of these markers is a deterioration warning:[2]

| Test | Finding | Prognostic implication |[1] |---|---|---| | Full blood count | Lymphopenia (under 1.0 × 10⁹/L); neutrophil/lymphocyte ratio over 3; mild thrombocytopenia then reactive thrombocytosis | Severity and mortality | | CRP | Raised, often 50 to 200 mg/L | Trajectory marker; rising means worsening | | Ferritin | Markedly raised, often 1000 or more | Macrophage activation | | D-dimer | Markedly raised | Coagulopathy, VTE, mortality | | LDH | Raised | Tissue injury; mortality marker | | IL-6 | Raised where available | Target of tocilizumab; trajectory marker | | Troponin / NT-proBNP | Raised | Cardiac injury; adverse | | ALT / AST | Mild transaminitis | Hepatic involvement | | Creatinine / urea | Raised | AKI; adverse | | Creatine kinase | Raised | Myositis or rhabdomyolysis | | Coagulation | Mildly prolonged PT and aPTT; low fibrinogen only in severe DIC-like states | Hypercoagulable; bleeding rare |

[1] [2]

Severity scores:[1]

• NEWS2 — seven physiological parameters (RR, SpO2, supplemental oxygen, temperature, systolic BP, heart rate, AVPU or GCS); aggregate 5 or more is urgent review, 7 or more is an emergency.
• ARDS — Berlin definition (reproduce verbatim): timing within 1 week of a known insult or new or worsening respiratory symptoms; bilateral opacities not fully explained by effusions, lobar collapse or nodules; origin of oedema not fully explained by cardiac failure or fluid overload; hypoxaemia with PEEP or CPAP at least 5 cmH2O — mild P/F 200 to 300, moderate 100 to 200, severe under 100.[1]

MIS-C work-up adds echocardiography (coronary aneurysm, ventricular dysfunction, effusion), troponin and NT-proBNP, ferritin, CRP, coagulation, IL-6, and SARS-CoV-2 serology (often positive even when PCR is negative).[1]

VTE work-up uses D-dimer (raised in COVID-19 anyway, so apply trajectory and pre-test probability), CT pulmonary angiography for PE (watch for subsegmental and saddle emboli), compression Doppler of the legs, and echocardiography for RV strain.[2]

Resuscitation — oxygen is the job

Run an ABCDE approach, isolate immediately under airborne or droplet precautions, and notify infection control.[1]

Oxygen therapy is the cornerstone of supportive care. Target SpO2 92 to 96% in most adults — 88 to 92% in COPD or type-2 respiratory failure risk, and never chase 100% in a CO2-retainer.[1]

Escalation ladder — step up guided by SpO2 and work of breathing:[1]

1. Nasal cannula (1 to 5 L/min).
2. Simple face mask (5 to 10 L/min) or non-rebreather mask (15 L/min) for immediate resuscitation.
3. High-flow nasal oxygen (HFNO) — up to 60 L/min, FiO2 up to 100%, humidified and well-tolerated. Monitor closely: HFNO failure means early intubation, not a longer trial.
4. CPAP or non-invasive ventilation — useful in hypoxaemic respiratory failure (some benefit; aerosol-generation risk — close-fitting mask and viral filter).
5. Invasive mechanical ventilation — when HFNO or NIV fails, or the patient has worsening respiratory failure despite maximal non-invasive support, altered consciousness, or haemodynamic instability. Intubate early, not as a crash can't-intubate-can't-oxygenate.
6. Veno-venous ECMO — for refractory severe ARDS in expert centres.[1]

Awake proning at the bedside (see Clinical Assessment) — start in cooperative patients with SpO2 under 92% on oxygen.[1]

The septic-shock bundle (Surviving Sepsis hour-1) applies to COVID-19 with shock: two large-bore cannulae, blood cultures, lactate, broad-spectrum antibiotics within 1 hour, balanced crystalloid 30 mL/kg, and noradrenaline for fluid-refractory shock; reassess fluid responsiveness before any further bolus.[1]

Start VTE prophylaxis on admission in every non-bleeding patient — this is not optional, and it is detailed in the drug-ladder section. Begin end-of-life and goals-of-care discussions early in advanced frailty or irreversible multi-organ failure.[1]

The severity-stratified drug ladder

Therapy is stratified by severity, and time-from-symptom-onset is the second axis: early disease is a viral problem (antivirals), late severe disease is a host problem (immunomodulators and anticoagulation).[3][1]

[1]

Mild disease (home, SpO2 at least 92%) — supportive care: rest, hydration, paracetamol 1 g QDS. Isolate per symptom or time-based criteria (see Prognosis). Antibiotics are NOT routine. Consider an outpatient antiviral if the patient is high-risk.[1]

The 5-day antiviral window — outpatients

High-risk mild or moderate outpatients, within 5 to 7 days of symptom onset, get an antiviral to prevent progression. The first-choice agent and the dose to quote:[7]

• Nirmatrelvir-ritonavir (Paxlovid) — 300 mg nirmatrelvir plus 100 mg ritonavir orally twice daily for 5 days (reduce to nirmatrelvir 150 mg plus ritonavir 100 mg BD if eGFR 30 to 60 mL/min; contraindicated if eGFR under 30 or in severe hepatic impairment). Nirmatrelvir inhibits the SARS-CoV-2 3CL protease; ritonavir boosts it by CYP3A inhibition. EPIC-HR cut hospitalisation or death by 89% in unvaccinated high-risk adults.[7]
• Remdesivir (outpatient, IV) — for those who cannot take Paxlovid: 200 mg IV on day 1, then 100 mg IV daily on days 2 and 3 (3-day course).[4]
• Molnupiravir — 800 mg orally twice daily for 5 days; only about a 30% reduction, so it is the fallback; avoid in pregnancy and in those of childbearing potential not using contraception.[7]

The trap that costs marks: ritonavir is a potent CYP3A inhibitor, so Paxlovid collides with statins, antiarrhythmics, anticoagulants, calcineurin inhibitors and many antiretrovirals — review the medication list and adjust or withhold interacting drugs for the 5-day course before you prescribe.[7]

On oxygen — dexamethasone, remdesivir, then the immunomodulators

Moderate-to-severe disease in a hospitalised patient on oxygen is combination therapy. Three drugs do the heavy lifting, each with a named trial behind it:[1]

Dexamethasone 6 mg PO or IV once daily for up to 10 days is the single most important mortality-reducing therapy in severe or critical COVID-19 — and the rule that governs it is the most examinable single fact in the topic.[3]

[3] [3]

Remdesivir (inpatient, IV) — 200 mg IV loading dose on day 1, then 100 mg IV daily for 4 more days (5 days total); extend to 10 days in the severely immunocompromised with prolonged replication. Mechanism: nucleotide-analogue inhibitor of SARS-CoV-2 RNA-dependent RNA polymerase.[4]

[4]

IL-6 inhibition — tocilizumab — 8 mg/kg IV (maximum 800 mg) as a single dose, repeatable once after 8 to 12 hours if no response. Indicated in severe or critical disease with hypoxaemia on oxygen and a rising inflammatory marker profile (CRP, ferritin) with rapid progression, particularly within 24 hours of new high-flow oxygen or ventilation. Mechanism: monoclonal antibody to the IL-6 receptor.[6]

[6]

JAK inhibition — baricitinib — 4 mg PO daily for up to 14 days (renal dose adjustment); an alternative to tocilizumab in selected severe or critical patients. Mechanism: JAK1 and JAK2 inhibition, blocking intracellular signalling downstream of multiple cytokines. Do not combine routinely with tocilizumab.[9]

Side-effects to monitor across the bundle: dexamethasone drives hyperglycaemia (often marked, may need insulin), secondary infection, neuromyopathy, psychiatric disturbance and GI bleeding; tocilizumab and baricitinib raise the risk of secondary bacterial or fungal infection.[9]

A corticosteroid plus remdesivir combination is the right opening move for the patient with new-onset hypoxaemia on oxygen.[1]

The disproven shelf — name it and refuse it: hydroxychloroquine (no benefit, arrhythmia and excess mortality), lopinavir-ritonavir (no benefit, GI side-effects), ivermectin (no benefit in well-designed trials), azithromycin (no benefit), and convalescent plasma in late disease (no benefit). Early-generation monoclonal antibodies (casirivimab-imdevimab, sotrovimab, regdanvimab) lost neutralising activity against Omicron sublineages, so their role is now limited; check current local neutralisation data.[1]

VTE prophylaxis — mandatory, with a dose fork

Pharmacological VTE prophylaxis is mandatory in every hospitalised non-bleeding COVID-19 patient. The hypercoagulable state is real and the PE rate is several-fold higher than in matched non-COVID inpatients.[2]

• Enoxaparin 40 mg subcutaneous once daily (or dalteparin 5000 IU SC OD); reduce to enoxaparin 20 mg SC OD if eGFR under 30, or use unfractionated heparin 5000 IU SC TDS in severe renal impairment.
• Therapeutic-dose anticoagulation is NOT routine in critically ill ICU patients — REMAP-CAP, ATTACC and ACTIV-4a showed therapeutic dosing was harmful in the critically ill.
• Consider therapeutic-dose LMWH in moderately ill (non-ICU) hospitalised patients with a high D-dimer (these trials showed benefit).
• Therapeutic anticoagulation is, of course, mandatory for confirmed VTE, PE or acute coronary syndrome.[2]

The ventilated ARDS lung — protect it

Lung-protective ventilation is the rule for COVID-19 ARDS, with PEEP individualised to the Type-L or Type-H phenotype:[1]

• Low tidal volume 6 mL/kg predicted body weight; plateau pressure under 30 cmH2O; driving pressure under 15 cmH2O.
• Prone positioning 16 hours per day in moderate-to-severe ARDS (P/F under 150) — improves oxygenation and reduces mortality.
• Neuromuscular blockade (cisatracurium) for severe asynchrony or P/F under 150 — short course.
• Inhaled pulmonary vasodilators (nitric oxide, epoprostenol) — rescue oxygenation only, no mortality benefit.
• VV-ECMO for refractory severe ARDS in an expert centre.[1]

Step-down and discharge — clinically stable, afebrile for 24 to 48 hours, SpO2 over 92% on room air for 24 hours, no organ-support requirement, stable comorbidity and a safe social situation. Continue thromboprophylaxis for 2 to 6 weeks post-discharge in high-risk patients.[1]

The subtypes that bite

MIS-C (and MIS-A) is a hospital emergency — persistent fever plus multi-organ involvement 2 to 6 weeks after SARS-CoV-2 infection. Manage with:[1]

• Supportive ICU for shock (fluids, vasoactive agents) and respiratory support.
• IV immunoglobulin (IVIG) 2 g/kg as a single infusion over 10 to 12 hours (maximum 100 g), plus methylprednisolone 1 to 2 mg/kg/day (pulse methylprednisolone 10 to 30 mg/kg/day in severe shock).
• Aspirin at antiplatelet dose (3 to 5 mg/kg/day, maximum 75 mg) for coronary-artery aneurysm prophylaxis; therapeutic anticoagulation if a large aneurysm or thrombus is present.
• Serial echocardiography for coronary aneurysms and cardiac function.
• Refractory cases — anakinra (IL-1 receptor antagonist) or infliximab.[1]

COVID-19 in pregnancy raises the risk of ICU admission, mechanical ventilation and preterm birth, with no convincing increase in vertical transmission. Dexamethasone 6 mg is safe and is the corticosteroid of choice for severe maternal COVID-19 (caveat: do not double-count it as routine antenatal fetal-lung-maturation dosing). Remdesivir is not contraindicated — benefit-risk favours use in hypoxaemic pregnant women. Tocilizumab can be used in life-threatening disease. mRNA vaccines are safe and recommended in pregnancy and lactation, and they reduce maternal severe disease and preterm birth. Timing of delivery is obstetric, not COVID-driven unless there is maternal compromise.[10]

COVID-19 in the immunocompromised — prolonged viral shedding (weeks to months, especially after rituximab, anti-CD20 or calcineurin inhibitors), higher mortality, and the substrate for variant emergence under prolonged replication. Strategies: prophylactic monoclonal antibodies where active against current variants, longer courses of remdesivir (10 days), early combination antiviral-immunomodulator therapy, and reduction of immunosuppression where possible.[1]

Long COVID (post-COVID condition) — WHO definition: onset within 3 months, duration at least 2 months, not explained by another diagnosis. Manifestations: fatigue (most common, often disabling), breathlessness, cognitive dysfunction ("brain fog"), persistent anosmia or ageusia, post-exertional malaise, autonomic dysfunction (POTS-like postural tachycardia), mental-health sequelae, persistent cough and sleep disturbance. Management is symptom-focused and rehabilitative — pacing for fatigue and post-exertional malaise (aggressive exercise reconditioning can worsen it), pulmonary and cognitive rehabilitation, and treatment of identifiable organ-specific disease.[1]

Paediatric COVID-19 is predominantly mild or asymptomatic; the Omicron era produces more upper-airway disease (croup, bronchiolitis-like). Vaccination is recommended from 6 months of age. Watch for MIS-C 2 to 6 weeks after infection — the principal paediatric emergency.[1]

Asymptomatic infection — isolate per local guidance (5 days plus a mask for 5 days per CDC, or test-based), no antiviral unless high-risk, and check for progression.[8]

Complications by system — the clock and the clot

Complications cluster by system, and two themes recur: the cytokine-driven multi-organ injury and the thrombotic tendency.[1]

• Pulmonary — ARDS, secondary bacterial pneumonia (S. pneumoniae, Staph aureus, Gram-negatives — suspect with new fever, purulent sputum and leucocytosis after initial improvement), pulmonary fibrosis (some responds to corticosteroid), pneumothorax and pneumomediastinum (barotrauma and spontaneous), pulmonary embolism, pleural effusion (uncommon, usually reactive).
• Cardiac — myocarditis (raised troponin, heart failure, arrhythmia; severe mimics ACS), pericarditis, new arrhythmias, Takotsubo cardiomyopathy, ACS or MI (in-situ thrombosis of a ruptured plaque or type-2 MI from hypoxaemia or sepsis), heart-failure exacerbation.
• Thrombotic — DVT, PE, MI, ischaemic stroke, mesenteric and unusual-site thromboses, catheter-related thrombosis; a coagulopathy resembling DIC but predominantly thrombotic (high D-dimer, often near-normal PT and aPTT, low fibrinogen only in severe cases).
• Neurological — encephalopathy (common in ICU), ischaemic stroke, intracerebral haemorrhage (rare, anticoagulation-related), seizures, Guillain-Barre syndrome, acute transverse myelitis, persistent anosmia, critical-illness polyneuropathy and myopathy.
• Renal — AKI (multifactorial — sepsis, cytokine, thrombotic microangiopathy, nephrotoxins; often needs RRT), proteinuria and haematuria.
• Hepatic and GI — transaminitis, cholestatic disease in severe cases, bowel ischaemia from mesenteric thrombosis, pancreatitis (rare), new-onset diabetes post-COVID.
• Endocrine — new-onset diabetes, adrenal insufficiency (critical illness or adrenal haemorrhage), subacute thyroiditis.
• Dermatological — chilblain-like "COVID toes", urticarial, maculopapular, livedoid and vesicular eruptions.[1]

Prognosis, disposition, and when they can leave

The overall symptomatic case-fatality rate is about 5% globally — but it varies tenfold by country, age and healthcare capacity, and the true infection-fatality rate is far lower (about 0.5 to 1% overall) because asymptomatic infection is under-diagnosed. Mortality rises exponentially with age — under 0.1% in the under-50s to over 15% in the over-80s — and comorbidity multiplies risk.[2]

Poor prognostic markers to reproduce as a list: older age, comorbidity (cardiac, diabetic, renal, respiratory, obesity, immunocompromise), SpO2 under 92% on room air, raised D-dimer, ferritin, CRP, LDH, troponin and IL-6, lymphocyte count under 0.8 × 10⁹/L, high neutrophil/lymphocyte ratio, low albumin, AKI, multilobar infiltrates, low PaO2/FiO2 ratio, and vaccination non-receipt.[2]

Disposition splits cleanly along the severity ladder:[1]

• Home — mild disease, SpO2 at least 94% on room air, no red flags; safety-net for worsening dyspnoea, chest pain, confusion or haemoptysis.
• Hospital — moderate or severe disease (SpO2 under 92% on room air, RR over 30, pneumonia, comorbidity decompensation, frailty or elderly, social concerns).
• ICU — severe or critical disease (ARDS with P/F under 200, septic shock, need for mechanical ventilation, multi-organ failure).[1]

Discharge when the patient is clinically improving, afebrile for 24 to 48 hours, with SpO2 over 92% on room air for 24 hours, no oxygen requirement, tolerating oral intake, stable comorbidity and a safe social situation. Consider post-discharge LMWH for 2 to 6 weeks in high-VTE-risk patients.[1]

Ending isolation — modern symptom or time-based criteria (CDC and WHO): at least 5 days from symptom onset with 24 hours fever-free and improving symptoms, then mask for 5 more days; severe or immunocompromised cases need longer, up to 20 days. A test-based strategy (two negative RATs 24 hours apart) is an alternative. For asymptomatic positives: 5 days from the positive test. Healthcare workers and the immunocompromised follow stricter protocols.[1]

Special populations and the vaccines

Elderly — atypical and blunted presentation (delirium, falls, anorexia, afebrile), higher mortality, and higher risk of delirium, frailty, secondary bacterial infection, aspiration and anticoagulation-related bleeding. Lower threshold to admit, protect against delirium, preserve function, and consider advance care planning.[1]

Pregnancy — more ICU admission, ventilation and preterm birth; mRNA vaccines safe and recommended; dexamethasone and remdesivir safe; tocilizumab in life-threatening disease; delivery is obstetric-led.[1]

Immunocompromised (transplant, chemotherapy, advanced HIV with low CD4, rituximab, calcineurin inhibitors) — prolonged shedding, higher mortality, risk of variant emergence, lower vaccine response; consider prophylactic mAbs where active, additional vaccine doses, longer antiviral courses, and reduction of immunosuppression where possible.[1]

Children — mostly mild; Omicron upper-airway phenotype; MIS-C 2 to 6 weeks post-infection; vaccination from 6 months; weight-based dosing for remdesivir, nirmatrelvir-ritonavir (Paediatric EPIC) and tocilizumab.[1]

CKD and dialysis — high-risk; renal dose adjustments of remdesivir, nirmatrelvir and enoxaparin (unfractionated heparin if eGFR under 30); careful fluid balance in dialysis; protect vascular access.[1]

Obesity (BMI 30 and over) — independent risk factor for severe disease; proning can be technically hard; weight-based dosing of LMWH and tocilizumab; lower threshold for ICU.[1]

The vaccines — platform by platform, and the two syndromes to name

Vaccination is the single most effective prevention and reduces severe disease by more than 90%. Know each platform, its efficacy and its signature adverse event:[10]

[10] [10]

• mRNA platform (Pfizer BNT162b2, Moderna mRNA-1273) — lipid-nanoparticle mRNA encoding spike; about 95% efficacy against symptomatic COVID-19. Adverse events: reactogenicity, lymphadenopathy, rare anaphylaxis, and mRNA-vaccine myocarditis — particularly in young males under 30 after the second dose, usually mild and self-limiting.[10]
• Viral vector (ChAdOx1 Covishield or AstraZeneca, Ad26.COV2.S Janssen, Sputnik V) — recombinant adenovirus encoding spike; lower reactogenicity than mRNA. The signature serious adverse event is vaccine-induced thrombosis and thrombocytopenia (VITT or TTS): an autoimmune-HIT-like syndrome with anti-PF4 antibodies, thrombosis at unusual sites (cerebral venous sinus, splanchnic), thrombocytopenia, onset 5 to 30 days post-vaccination. Treat with a non-heparin anticoagulant (argatroban, danaparoid, fondaparinux or a DOAC) plus IVIG; avoid heparin and platelet transfusion. Most countries restricted viral-vector vaccines to older adults or switched to mRNA.[10]
• Inactivated (Covaxin BBV152, CoronaVac Sinovac) — whole inactivated virion plus alum or adjuvant; lower efficacy against symptomatic disease but good protection against severe disease; very low rates of serious adverse events.
• Protein subunit (Novavax Nuvaxovid, Corbevax) — recombinant spike plus adjuvant.
• Heterologous prime-boost (mixing platforms) improves immunogenicity and is widely practised.[10]

The trials that changed the pandemic

The landmark trials a final-prof candidate cites by name, population and result — and what each changed:[1]

• RECOVERY — dexamethasone 6 mg OD: mortality 41% to 28% ventilated, 26% to 21% on oxygen, no benefit off oxygen (see the drug ladder).[3]
• ACTT-1 — remdesivir shortened recovery from 15 to 10 days in early hypoxaemic disease.[4]
• REMAP-CAP tocilizumab and baricitinib — both reduced mortality and increased organ-support-free days in severe or critical disease within 24 hours of new high-flow oxygen or ventilation with rising inflammatory markers.[6]
• EPIC-HR — nirmatrelvir-ritonavir cut hospitalisation or death by 89% in unvaccinated high-risk symptomatic outpatients within 5 days of onset.[7]
• Polack et al, BNT162b2 — 95% efficacy against symptomatic COVID-19 in the pivotal phase-3 trial.[10]
• RECOVERY, WHO and SOLIDARITY hydroxychloroquine and lopinavir-ritonavir arms — no benefit; abandoned.
• REMAP-CAP, ATTACC and ACTIV-4a therapeutic-dose anticoagulation — harmful in critically ill ICU patients; modest benefit in moderately ill (non-ICU) hospitalised patients with high D-dimer.
• MOVe-OUT molnupiravir — about a 30% reduction in hospitalisation or death; less than Paxlovid.[1]

Guideline deltas to name calmly: the WHO Living Guideline (2023) recommends dexamethasone for severe or critical disease, remdesivir for high-risk moderate, tocilizumab or baricitinib for severe or critical with rapid progression, nirmatrelvir-ritonavir for high-risk non-severe, and recommends against hydroxychloroquine, lopinavir-ritonavir, ivermectin and convalescent plasma. NIH (US) prefers nirmatrelvir-ritonavir for high-risk outpatients and dexamethasone plus remdesivir plus or minus baricitinib or tocilizumab for the hospitalised. NICE (UK) NG191 or NG188 is dexamethasone-based, with tocilizumab and sarilumab for severe or critical. ICMR or AIIMS India gives dexamethasone for severe, remdesivir for early moderate (within 10 days), tocilizumab for severe with rapid progression, LMWH prophylaxis for all hospitalised, restricted convalescent plasma, and does not recommend ivermectin.[1]

Controversies to acknowledge, not dodge: the role of ivermectin (extensively hyped, no high-quality benefit), early corticosteroids (harmful in non-hypoxaemic disease — reserve for oxygen-requiring patients), the prophylactic-versus-therapeutic anticoagulation dose (current consensus: prophylactic, with therapeutic for selected high D-dimer), the timing of intubation (modern practice favours early over waiting for a crash), and mixing vaccine platforms (heterologous schedules increasingly evidence-supported).[1]

How COVID-19 patients come to harm (the preventable list)

• Missing silent hypoxaemia — sending the chatty SpO2 84% patient home with paracetamol. Measure SpO2 on room air in every case; walking tests to unmask it.[1]
• Late intubation — waiting for a crash instead of recognising HFNO or NIV failure (rising RR, rising work of breathing, falling SpO2).[1]
• Dexamethasone off oxygen — the RECOVERY rule broken: steroid given to a patient not on oxygen, where it brings no benefit and possible harm.[3]
• Over-using antibiotics in a viral illness — reserve for documented or suspected secondary bacterial infection.[1]
• Missing secondary bacterial infection in the deteriorating ventilated patient — repeat cultures, procalcitonin, bronchoscopy if needed.[2]
• Missing the pulmonary embolism in a deteriorating inpatient — high index of suspicion, CTPA, and remember D-dimer is raised in COVID-19 anyway.[2]
• No VTE prophylaxis in a hospitalised patient, and forgetting post-discharge prophylaxis in the high-risk.[2]
• Using disproven therapies — hydroxychloroquine, lopinavir-ritonavir, ivermectin, late convalescent plasma.[1]
• Inappropriate oxygen targeting in COPD — target 88 to 92%, not 100%, to avoid CO2 retention.[1]
• Neglecting proning in the awake and the ventilated patient with severe ARDS.[1]

The mantra, and the mnemonic

[1] [1]

The mantra: oxygen on, steroid on, heparin on, watch the cytokine phase.[1][3]

Ward-round test — three stems

Stem 1 — the man from the top of the topic (answer)

The 62-year-old diabetic with BMI 33, day 6 of a flu-like illness, chatting on his phone with SpO2 84% on room air and a clear chest. What do you do in the next ten minutes, and what is the single most important drug you start? Model: This is severe COVID-19 with silent hypoxaemia — the preserved-compliance Type-L lung lets him talk while desaturating. Do not send him home. Admit, isolate, start supplemental oxygen to target SpO2 92 to 96%, and because he is now on oxygen, start dexamethasone 6 mg OD (RECOVERY — mortality benefit only in oxygen-requiring patients). Send nasopharyngeal RT-PCR, inflammatory markers (CRP, ferritin, D-dimer, LDH, IL-6, lymphocyte count) and chest imaging, with a 6-minute walk test after stabilisation to confirm the desaturation. Add remdesivir 200 mg IV load then 100 mg OD for 5 days (within the 10-day antiviral window) and enoxaparin 40 mg SC OD for VTE prophylaxis. Watch the trajectory around days 7 to 10 for the cytokine phase.[1][3]

Stem 2 — improving, then worse at day 8 (answer)

A 55-year-old on 4 L via nasal cannula for COVID-19 pneumonia was improving until day 8, when SpO2 falls, CRP jumps from 60 to 180 mg/L, ferritin climbs and D-dimer doubles. He is now on 10 L via HFNO. What is happening, and what drug do you reach for? Model: This is the day-7-to-10 cytokine phase — the host inflammatory response catching fire, not new viral replication. The trigger for immunomodulation is exactly this picture: hypoxaemia on oxygen with a rising inflammatory marker profile and rapid progression, particularly within 24 hours of escalation to high-flow oxygen or ventilation. Start tocilizumab 8 mg/kg IV (maximum 800 mg) as a single dose (repeatable once after 8 to 12 hours) — REMAP-CAP showed mortality and organ-support benefit — or baricitinib 4 mg PO OD as an alternative; do not combine the two routinely. Continue dexamethasone, consider therapeutic-dose anticoagulation for the high D-dimer (moderately ill, non-ICU), and escalate to ICU early if HFNO fails.[6][9]

Stem 3 — the high-risk outpatient on day 3 (answer)

A 70-year-old with diabetes, CKD (eGFR 45 mL/min) and heart failure tests positive on day 3 of mild symptoms — sore throat, low-grade fever, SpO2 96% on room air. The registrar reaches for a Paxlovid prescription. What checks must happen first? Model: This is a high-risk outpatient within the 5-day antiviral window — exactly the EPIC-HR population in whom nirmatrelvir-ritonavir 300/100 mg PO BD for 5 days cut hospitalisation or death by 89%. But before prescribing, check the eGFR and the medication list: at eGFR 30 to 60 the dose is reduced to nirmatrelvir 150 mg plus ritonavir 100 mg BD, and ritonavir is a potent CYP3A inhibitor that collides with his statin, his anticoagulant and possibly his antiarrhythmic — adjust or withhold interacting drugs for the 5-day course. If the interactions or an eGFR under 30 make Paxlovid unsuitable, give outpatient remdesivir 200 mg IV on day 1 then 100 mg IV on days 2 and 3. He does not need dexamethasone — he is not on oxygen, and steroid off oxygen is harm.[7][3]

References

1. [1]Huang C, Wang Y, Li X, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China Lancet, 2020.PMID 31986264
2. [2]Zhou F, Yu T, Du R, et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study Lancet, 2020.PMID 32171076
3. [3]Horby P, Lim WS, Emberson JR, et al. Dexamethasone in Hospitalized Patients with Covid-19 N Engl J Med, 2021.PMID 32678530
4. [4]Beigel JH, Tomashek KM, Dodd LE, et al. Remdesivir for the Treatment of Covid-19 - Final Report N Engl J Med, 2020.PMID 32445440
5. [5]Shi H, Han X, Jiang N, et al. Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study Lancet Infect Dis, 2020.PMID 32105637
6. [6]Rosas IO, Bräu N, Waters M, et al. Tocilizumab in Hospitalized Patients with Severe Covid-19 Pneumonia N Engl J Med, 2021.PMID 33631066
7. [7]Hammond J, Leister-Tebbe H, Gardner A, et al. Oral Nirmatrelvir for High-Risk, Nonhospitalized Adults with Covid-19 N Engl J Med, 2022.PMID 35172054
8. [8]Han D, Li R, Han Y, et al. COVID-19: Insight into the asymptomatic SARS-COV-2 infection and transmission Int J Biol Sci, 2020.PMID 33061797
9. [9]Burrage DR, Koushesh S, Sofat N. Immunomodulatory Drugs in the Management of SARS-CoV-2 Front Immunol, 2020.PMID 32903555
10. [10]Polack FP, Thomas SJ, Kitchin N, et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine N Engl J Med, 2020.PMID 33301246