Case · Presentation

She had both doses. That may not be enough.

Sarah C is 8, 25 kg, 125 cm, with systemic juvenile idiopathic arthritis diagnosed at age 6 and managed for the past two years on infliximab 6 mg/kg intravenously every 8 weeks with subcutaneous methotrexate 1 mg/kg weekly. No known drug allergies.

She returned from a class trip to Japan four days ago. Forty‑eight hours after the return, one of her classmates on the trip was diagnosed with varicella. Today the school notified the class.

She received the 2‑dose varicella vaccination on schedule in early childhood. She is asymptomatic — no fever, no rash, no fatigue, no systemic complaints. Her mother: “I’m very concerned about Sarah.”

Varicella vaccine

2 doses, on schedule

On infliximab

2 years

Order the workup or use the arrow keys

Case · Workup

Not all test results would change what you do.

The varicella‑zoster antibody test and the VZV PCR are both unnecessary to determine the need for post‑exposure prophylaxis. Detection of antibodies such as VZV IgG through serologic testing does not necessarily indicate true protective immunity in immunosuppressed individuals, such as those on infliximab therapy (AAP Red Book, 2024).

Proceeding without testing is the prudent action. The risk of relying on antibody testing here is misinterpretation, delaying appropriate intervention.

She is classified high risk of VZV complications. Infliximab suppresses her immune response (Khanna R and Feagan BG, 2015), reducing her ability to maintain vaccine‑acquired immunity and leaving her vulnerable to pneumonitis, encephalitis and disseminated varicella (Levin MJ et al, 2019). Recent exposure to a confirmed case during the incubation period, 10–21 days, heightens the risk.

Go to the decision

Case · Decision

What do you give her, and how fast?

Asymptomatic, vaccinated, immunosuppressed, and four days from a confirmed exposure. Choose one.

• AVARIZIG
• BAcyclovir, prophylactic dosing
• COral varicella vaccine
• DTopical antiviral creams
• EWatchful waiting

Lock in my answer Select a treatment to continue

Case · Verdict

Borrowed antibody, now. Not a test, not a wait.

• AVARIZIGAppropriateFirst‑line post‑exposure prophylaxis for immunocompromised individuals. Optimal within 96 hours of exposure; the CDC suggests it may still be beneficial up to 10 days post‑exposure (Levin MJ et al., 2019). Safe and effective in immunocompromised patients (CDC, 2013).
• BAcyclovir, prophylactic dosingNot appropriateOral acyclovir or valacyclovir from day 7 is an alternative only when VARIZIG is unavailable (AAP Red Book, 2024). Guidance here is limited, and oral therapy alone risks missing the 96‑hour window if it fails (Lachiewicz AM and Srinivas ML, 2020).
• COral varicella vaccineNot appropriateContraindicated. Live attenuated varicella vaccines carry a risk of vaccine‑associated disseminated infection in immunocompromised patients such as those on infliximab (CDC Yellow Book, 2024).
• DTopical antiviral creamsNot appropriateUseful for localised herpes simplex infections, but with no proven efficacy against systemic VZV infection (Gnann, 2007).
• EWatchful waitingNot appropriateNot recommended after exposure in an immunocompromised patient — high risk of severe varicella: pneumonitis, encephalitis, hepatitis (Levin MJ et al., 2019).

• ThenObserve up to 28 days post‑exposure (CDC, 2013); follow‑up with rheumatology and immunology.
• AndAn emergency plan — the emergency room for high fever, respiratory distress, confusion or seizures.

See what settles it

Case · Evidence

Vaccinated is not the same as protected.

Immunosuppressive and anti‑TNF medications like infliximab can reduce vaccine effectiveness, and even vaccinated children may still develop varicella. VZV is highly contagious, with an infection rate of about 85% among susceptible individuals following exposure (CDC Yellow Book, 2024).

• 01Infliximab suppresses cellular immunity, an effect that may be prolonged with regular, intermittent administration. Given during the incubation phase of primary VZV infection, that suppression can facilitate viral dissemination (Balato N et al., 2009).
• 02Serology cannot answer the question. VZV IgG does not necessarily indicate true protective immunity in immunosuppressed patients (AAP Red Book, 2024) — and testing costs time the window does not have.
• 03The window is the constraint. Optimal efficacy is achieved within 96 hours of exposure, and VARIZIG remains effective up to 10 days, allowing for delayed recognition (Levin MJ et al., 2019). Oral therapy alone may close that window if it proves ineffective (Lachiewicz AM and Srinivas ML, 2020).
• 04Prior vaccination changes severity, not eligibility. Children on immunosuppressive therapy exposed to VZV are at higher risk of severe complications — cellulitis, sepsis, pneumonitis, encephalitis, hepatitis — despite prior vaccination (Levin MJ et al., 2019).

Start case