What precautions should be taken and what adverse reactions may occur after receiving the varicella vaccine?

Vaccination against varicella (chickenpox) is a safe and highly effective way to prevent infection with the varicella-zoster virus. The varicella vaccine is a live attenuated vaccine, typically administered as a two-dose series—first dose at age 12–15 months and second dose at age 4–6 years. For susceptible older children, adolescents, and adults, two doses are recommended with at least 28 days between doses.

Before vaccination, healthcare providers should screen for contraindications and precautions. Absolute contraindications include severe immunosuppression (e.g., due to hematologic malignancies, solid organ or hematopoietic stem cell transplantation, high-dose corticosteroid therapy—defined as ≥20 mg/day of prednisone or equivalent for ≥2 weeks), pregnancy, and a history of anaphylaxis to a prior dose or any vaccine component (e.g., gelatin or neomycin). A moderate or severe acute illness—with or without fever—is considered a precaution; vaccination should be deferred until recovery. Mild illnesses, such as upper respiratory tract infections, are not reasons to delay immunization.

Common adverse reactions are generally mild and self-limiting. Local reactions—including pain, redness, or swelling at the injection site—occur in approximately 20–30% of recipients. Systemic reactions such as low-grade fever, fatigue, headache, or mild rash (often localized and non-contagious) may occur in up to 5–10% of individuals, typically within 5–26 days post-vaccination. A varicella-like rash—characterized by ≤5 discrete, vesicular lesions—may appear in about 3–5% of vaccinees, usually around 5–10 days after vaccination; these lesions are typically few in number, resolve spontaneously, and pose minimal transmission risk.

Serious adverse events are exceedingly rare. Anaphylaxis occurs at a rate of approximately 1 case per million doses. There is no credible evidence linking the varicella vaccine to autism, encephalitis, or Guillain-Barré syndrome. Post-licensure surveillance continues to support the vaccine’s favorable safety profile. As with all vaccines, providers should document administration accurately and counsel patients on recognizing signs of allergic reaction (e.g., hives, wheezing, swelling of the face or throat) and seeking immediate medical attention if they occur.