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Varicella exposure during rituximab-associated immunosuppression — SCE Rheumatology MCQ

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ModerateImmunosuppressionVaricella exposure during rituximab-associated immunosuppressionSCE Rheumatology

A 54-year-old woman with granulomatosis with polyangiitis received maintenance rituximab 5 months ago. She takes prednisolone 5 mg daily and has stable disease. Three days ago, she spent 30 minutes face to face with a colleague in a small office. The colleague had developed a generalised chickenpox rash that morning. She cannot recall having chickenpox and has no documented varicella vaccination. Urgent quantitative testing shows varicella-zoster virus IgG 82 mIU/mL. She remains asymptomatic, her eGFR is 78 mL/min/1.73 m², and she has no contraindication to oral antiviral therapy. Which post-exposure strategy is most appropriate?

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Correct answer: E — Start oral valaciclovir 1,000 mg three times daily on day 7 after exposure and continue through day 14

Explanation lettering: C = shown as A · E = shown as C · A = shown as E

This was a significant exposure: face-to-face contact in a small room occurred while the index case had infectious chickenpox. Rituximab within the preceding 6 months meets the UKHSA definition of immunosuppression, and previous infection or vaccination history is not considered a reliable marker of immunity in this population. Her quantitative VZV IgG is below the 150 mIU/mL threshold, confirming that post-exposure prophylaxis is indicated. UKHSA recommends oral aciclovir or valaciclovir as first-line prophylaxis for susceptible immunosuppressed contacts, given from day 7 to day 14 after exposure. The adult valaciclovir regimen is 1,000 mg three times daily. B starts treatment too early; unlike many antimicrobial prophylaxis regimens, varicella antivirals are deliberately commenced on day 7. C is reserved principally for contacts unable to receive oral antivirals; historical intramuscular VZIG is no longer available in the UK. D is inappropriate because live varicella vaccine is contraindicated during clinically significant immunosuppression. E would be appropriate if exposure were not significant or VZV IgG were at least 150 mIU/mL, but delayed treatment after rash onset does not replace indicated prophylaxis in this susceptible high-risk patient.

Reference: Guidelines on post-exposure prophylaxis for varicella or shingles (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 Immunisation against infectious disease: Varicella chapter (7 April 2026) — https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/456562/Green_Book_Chapter_34_v3_0.pdf