In general, side-effects from varicella-containing vaccines are mild and self-limiting, and include local reactions, fever and mild papulo-vesicular rash in normal healthy individuals. In approximately 1–3 percent of immunised children, a localised rash develops, and in an additional 3–5 percent a generalised varicella-like rash develops. These rashes typically consist of two to five lesions and may be maculopapular rather than vesicular; lesions usually appear 5 to 26 days after immunisation.24
In healthy vaccinees, transmission of vaccine virus has been exceedingly rare, with only 10 documented occurrences from nine vaccinees (one vaccinee transmitted virus to two other people), most commonly after household exposures.17 Err on the side of caution and isolate the vaccinee if a post-immunisation rash occurs, particularly if they are household contacts of immunosuppressed individuals. If an immunosuppressed individual inadvertently comes in contact with a vaccinee who has a varicella-like rash, the administration of zoster immunoglobulin (ZIG, for use after exposure to varicella or zoster) and/or acyclovir should be considered (see below).24 Intravenous acyclovir may be required for the immunosuppressed individual if symptoms develop.24
The Oka strain of varicella used in the available vaccines can establish latent ganglionic infection in vaccinees and later reactivate to produce clinical zoster (shingles). The risk of zoster is lower, and the clinical severity milder, in healthy vaccinees than in naturally infected children. A cohort study in children with acute lymphoblastic leukaemia (who have a high rate of zoster in childhood) showed that vaccinees had less than one-ﬁfth the zoster rate of their naturally infected counterparts.21 No cases of HZ in vaccinated adults caused by the Oka strain have been recorded.17
Compared with the use of MMR vaccine and varicella vaccine at the same visit, use of MMRV vaccine results in one fewer injection but is associated with a higher risk of fever and febrile seizures 5 to 12 days after the first dose among children aged 12–23 months (approximately one extra febrile seizure for every 2300–2600 MMRV vaccine doses).25 After the second dose, there are no differences in incidence of fever, rash or febrile seizures among recipients of MMRV vaccine compared with recipients of MMR and varicella vaccine.
This is why MMRV vaccine is not recommended as a first dose for children prior to their fourth birthday (approximately 97 percent of febrile seizures occur in children before age 4 years). MMRV vaccine can be given as a first dose to children after their fourth birthday, and as a second dose to children of any age (15 months to 12 years).
(See also section 11.7 for expected responses and adverse events following immunisation with MMR vaccine.)