The Chickenpox (Varicella) Vaccine: What Parents Should Know

Why chickenpox is worth preventing

Chickenpox (varicella) is often imagined as an inevitable, mild childhood rite of passage. For most healthy children it is uncomfortable but manageable. However, complications are more common than many parents realize: bacterial skin infections from scratched blisters, pneumonia, encephalitis (brain inflammation), and hospitalization all occur — primarily in otherwise healthy children, not just in those with underlying conditions 1Ref 1Centers for Disease Control and Prevention (2024).Chickenpox Vaccination.Two-dose schedule, 90% effectiveness, historical disease burden (hospitalizations and deaths before vaccination), and 97% reduction in cases since vaccination began.

Before routine vaccination, chickenpox caused roughly 100–150 deaths and more than 10,000 hospitalizations in the United States each year. Since the two-dose program was fully implemented, chickenpox cases and related deaths have fallen by more than 97% 1Ref 1Centers for Disease Control and Prevention (2024).Chickenpox Vaccination.Two-dose schedule, 90% effectiveness, historical disease burden (hospitalizations and deaths before vaccination), and 97% reduction in cases since vaccination began. Complications are more frequent in adolescents and adults who get chickenpox, which is another reason to vaccinate in early childhood rather than waiting.

Why two doses are needed

One dose of the varicella vaccine provides strong protection against severe disease but only about 80–85% protection against any infection. Two doses bring protection against any chickenpox to approximately 90% and provide near-complete protection against severe disease 1Ref 1Centers for Disease Control and Prevention (2024).Chickenpox Vaccination.Two-dose schedule, 90% effectiveness, historical disease burden (hospitalizations and deaths before vaccination), and 97% reduction in cases since vaccination began.

The second dose at age 4 to 6 also provides a meaningful immune-system boost — it is not simply a catch-up for children who did not respond to the first dose. Families whose children received only one dose under an older schedule can get the second dose at any time; the child's provider can advise on timing 2Ref 2Centers for Disease Control and Prevention (2024).Varicella Vaccine Recommendations.Two-dose schedule details, MMRV vs separate administration, contraindications including immunocompromised patients and pregnancy, breakthrough varicella description.

What happens if a vaccinated child still gets chickenpox

It is possible — though uncommon — for a vaccinated child to develop what is called 'breakthrough varicella.' In most cases, this is a milder illness: fewer spots (often fewer than 50, and sometimes more pimple-like than blister-like), low or no fever, and a shorter course 2Ref 2Centers for Disease Control and Prevention (2024).Varicella Vaccine Recommendations.Two-dose schedule details, MMRV vs separate administration, contraindications including immunocompromised patients and pregnancy, breakthrough varicella description.

Breakthrough varicella can still spread to others, so a child with any active chickenpox — vaccinated or not — should stay home from school or daycare until all lesions have crusted over. Breakthrough disease after only one dose is one reason the two-dose schedule is now standard.

The varicella vaccine and shingles

The varicella vaccine contains a live-attenuated (weakened) form of the varicella-zoster virus. Like natural chickenpox infection, the vaccine virus can theoretically remain dormant in nerve tissue and reactivate as shingles later in life 3Ref 3Centers for Disease Control and Prevention (2024).Chickenpox (Varicella) Vaccine Safety.Shingles risk from vaccine-strain virus, documented cases of vaccine-strain transmission (only 11 since 1995), overall favorable safety profile across 212 million doses.

However, studies have found that the weakened vaccine strain is significantly less likely to reactivate than wild-type varicella. Only 11 documented cases of vaccine-virus transmission to unvaccinated persons have been recorded since 1995 across hundreds of millions of doses 3Ref 3Centers for Disease Control and Prevention (2024).Chickenpox (Varicella) Vaccine Safety.Shingles risk from vaccine-strain virus, documented cases of vaccine-strain transmission (only 11 since 1995), overall favorable safety profile across 212 million doses. Vaccinated children appear to have a lower overall risk of shingles in childhood and young adulthood than children who had natural chickenpox, though surveillance continues as vaccinated cohorts age.

Who should not get the vaccine

The varicella vaccine is a live-attenuated vaccine, so there are specific groups for whom it is not recommended: children with significant immunodeficiency (including those on certain chemotherapy or immunosuppressive medications), children with a severe allergy to any vaccine component, and pregnant individuals 2Ref 2Centers for Disease Control and Prevention (2024).Varicella Vaccine Recommendations.Two-dose schedule details, MMRV vs separate administration, contraindications including immunocompromised patients and pregnancy, breakthrough varicella description. Healthcare providers follow a standard contraindication and precaution checklist before administering any live vaccine.

Children with mild egg allergy, a mild illness on the day of the visit, or a family member who is pregnant are generally still eligible — the provider reviews the individual situation at each visit and makes the determination. The combined MMR-varicella vaccine (MMRV) is sometimes offered for the first dose; it carries a slightly higher rate of fever and febrile seizure in the 5–12 days after the first dose compared to giving separate MMR and varicella injections. The absolute difference in febrile-seizure risk is small — approximately 4 additional febrile seizures per 10,000 first doses — and providers weigh this against the benefit of one fewer injection when choosing the formulation 2Ref 2Centers for Disease Control and Prevention (2024).Varicella Vaccine Recommendations.Two-dose schedule details, MMRV vs separate administration, contraindications including immunocompromised patients and pregnancy, breakthrough varicella description.

Catch-up and older children

Children who missed varicella vaccination on the standard schedule can receive catch-up doses at any age. The CDC publishes a catch-up immunization schedule that providers use to bring children current without unnecessary repetition of doses 4Ref 4Centers for Disease Control and Prevention (2025).Catch-up Immunization Schedule for Children and Adolescents.Catch-up vaccination guidance: a series does not need to be restarted regardless of elapsed time between doses. Older children and adolescents who have never had chickenpox or been vaccinated should receive two doses at least 28 days apart. If a child's chickenpox history is uncertain, vaccination is safe even if they already have immunity — there is no harm in vaccinating someone who is already immune.