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Significant varicella exposure in a susceptible pregnant woman — MSRA MCQ

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HardInfectious DiseasesSignificant varicella exposure in a susceptible pregnant womanMSRA

A 30-year-old woman who is 18 weeks pregnant contacts her GP after her 5-year-old son is diagnosed with chickenpox. His rash began 5 days ago and he continues to develop vesicles. They live together and she has provided all of his care. She has no history of chickenpox or shingles and has not received varicella vaccine. An urgent VZV IgG result obtained today is 42 mIU/mL. She is well, has normal renal function, no malabsorption, and can take oral medication. She is not taking any regular medicines. Which is the most appropriate post-exposure management plan?

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Correct answer: E — Provide oral aciclovir 800 mg four times daily, to start 48 hours from now and continue for 7 days

This woman needs varicella post-exposure prophylaxis: she is pregnant, has had continuous household exposure to infectious chickenpox, and is susceptible (VZV IgG below 100 mIU/mL). For a household contact, the exposure date is defined as the date of rash onset in the index case, rather than the date of last contact. Her son’s rash began 5 days ago, so she should start antiviral prophylaxis on day 7 after rash onset: in 48 hours. Current UKHSA guidance recommends oral aciclovir 800 mg four times daily for 7 days, starting on day 7 after exposure, for susceptible pregnant women at any gestation. Starting immediately is incorrect because early aciclovir prophylaxis is less effective. Intravenous immunoglobulin is reserved for people unable to take oral antivirals, such as where there is malabsorption or relevant renal toxicity. Reassurance alone is inappropriate because pregnancy and confirmed susceptibility meet PEP criteria. Delaying treatment until day 14 misses the recommended prophylactic window; if presentation is after day 7, treatment may be started up to day 14, but should not be deferred until then.

Reference: UKHSA: Guidelines on post-exposure prophylaxis (PEP) for varicella or shingles (Updated 19 March 2026) — https://www.gov.uk/government/publications/post-exposure-prophylaxis-for-chickenpox-and-shingles/guidelines-on-post-exposure-prophylaxis-pep-for-varicella-or-shingles-january-2023 UKHSA: Guidelines on post-exposure prophylaxis (PEP) for varicella or shingles (Updated 19 March 2026) — https://www.gov.uk/government/publications/post-exposure-prophylaxis-for-chickenpox-and-shingles/guidelines-on-post-exposure-prophylaxis-pep-for-varicella-or-shingles-january-2023 UKHSA: Guidelines on post-exposure prophylaxis (PEP) for varicella or shingles (Updated 19 March 2026) — https://www.gov.uk/government/publications/post-exposure-prophylaxis-for-chickenpox-and-shingles/guidelines-on-post-exposure-prophylaxis-pep-for-varicella-or-shingles-january-2023