Explaining varicella, exclusion and post-exposure prophylaxis — OSCE

Candidate instructions (8-minute station)

You are the paediatric registrar in the clinic. A 4-year-old child who has received both varicella vaccine doses has developed a mild rash over the last two days — a handful of vesicles, a slight fever, and some itch. The rash is confirmed as breakthrough varicella. The child is otherwise well and recovering. At home, the family has a 2-week-old newborn niece staying with them, and the child's mother is 28 weeks pregnant. ^[3]

Your tasks are: ^[2]

1. Explain the diagnosis of breakthrough varicella in plain language, and reassure the family that the vaccine still did its job. ^[3]
2. Explain the exclusion plan — that the child should stay home and away from vulnerable contacts until every lesion has crusted. ^[2]
3. Explain why the newborn niece and the pregnant mother need urgent assessment and post-exposure prophylaxis, and what that involves. ^{[2] [4]}
4. Address the father's confusion that a fully vaccinated child caught chickenpox at all. ^[3]

You are not expected to prescribe doses for the newborn yourself without senior review — flag that the newborn needs same-day assessment because varicella in a young infant can be severe. ^[4]