Varicella vaccine is very safe. About 20% of vaccine recipients will have minor injection site complaints, such as pain, swelling, or redness. About 7% develop fever. Fewer than 5% of recipients develop a localized or generalized varicella-like rash 5 to 26 days after vaccination. These rashes have an average of 2 to 5 lesions and may be maculopapular rather than vesicular. Side effects are less common after the second dose of varicella vaccine. Serious adverse reactions following varicella vaccine are uncommon.
Last reviewed:
August 12, 2026
If you believe the child had varicella disease (that is, breakthrough varicella) after the first dose, the child does not need another dose. If you are uncertain whether the child had varicella or a rash related to varicella vaccination, the second dose should be administered on schedule. If in doubt, give the second dose. If this was a case of breakthrough varicella, a second dose will not be harmful.
Last reviewed:
August 12, 2026
You cannot distinguish a mild case of varicella disease from a rash caused by the vaccine. The child may have been infected with varicella at about the same time s/he was vaccinated. The risk of transmission if the rash was caused by vaccine is very small; however, the conservative approach would be to treat the child as if s/he had chickenpox and restrict her/his activities until all the lesions crust.
Last reviewed:
August 12, 2026
Breakthrough varicella represents replication of wild varicella virus in a vaccinated person. Although most breakthrough disease is very mild, the child is contagious and activities should be restricted to the same extent as an unvaccinated person with varicella disease.
Last reviewed:
August 12, 2026
Available data suggest that healthy children are unlikely to transmit vaccine virus. Transmission of vaccine virus to a household contact has rarely been documented. It appears that transmission of vaccine virus occurs mostly, or perhaps even exclusively, when the vaccinated person develops a rash following vaccination.
Last reviewed:
August 12, 2026
Transmission of varicella vaccine virus is rare. However, if a pregnant or immunosuppressed household contact of a vaccinated person is known to be susceptible to varicella, and if the vaccinee develops a rash 7 to 21 days following vaccination, it is prudent that they avoid prolonged close contact with the susceptible person until the rash resolves.
Last reviewed:
August 12, 2026
It is not known if the infant will respond to the vaccine but no specific side effects except those normally seen after varicella vaccination. Clinic procedures should be reviewed to prevent an administration error from happening again. The dose should not be counted, and the child should be revaccinated on schedule at 12 through 15 months of age.
Last reviewed:
August 12, 2026
