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MMRV showed higher risk for febrile seizures vs. MMR, varicella
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Measles-mumps-rubella-varicella vaccine and measles-mumps-rubella and varicella vaccines had comparable risk for numerous adverse events, although the former had an increased risk for seizure and fever 7 to 10 days after vaccination.
In 2008, CDC testing indicated children aged 12 to 23 months had an increased risk for seizures after measles-mumps-rubella-varicella vaccine (MMRV; Proquad, Merck), according to study researcher Nicola P. Klein, MD, PhD, of Kaiser Permanente Vaccine Study Center in Oakland, Calif., and colleagues.
Nicola P. Klein
Follow-up testing indicated MMRV is associated with a twofold increased risk for fever and febrile seizures 7 to 10 days after vaccination compared with measles-mumps-rubella (MMR) and varicella vaccines.
To determine if MMRV receipt increased risk for other adverse events, Klein and colleagues assessed children aged 12 to 23 months from the CDC’s Vaccine Safety Datalink who received MMRV or separately administered, same-day MMR plus varicella vaccines. Researchers assessed risk for seven outcomes, including anaphylaxis, immune thrombocytopenia purpura, ataxia, arthritis, encephalitis/meningitis/encephalopathy, acute disseminated encephalomyelitis and Kawasaki disease.
Evaluation included 123,200 MMRV and 584,987 MMR plus varicella doses administered from 2000 to 2012.
Risk for the main outcomes was low, according to researchers, and risk differences between MMRV and MMR plus varicella were not statistically significant. Risk difference for seizure, however, was significant; analysis of seizures after October 2008 indicated MMRV was associated with a twofold increased risk for seizure 7 to 10 days after vaccination (RR=1.99; 95% CI, 1.08-3.53).
Secondary analyses that compared risk shortly after vaccination vs. 57 to 180 days after vaccination indicated both vaccines had increased risk for immune thrombocytopenia purpura and decreased risk for ataxia.
“This study did not identify any new safety concerns associated with MMRV or MMR plus varicella vaccines. There was no statistically significant difference in risk for any of the seven main outcomes evaluated,” Klein and colleagues wrote, “[though] power was limited for some outcomes, and ongoing monitoring is warranted.”
Disclosure: Klein and two other researchers report financial ties with Merck and GlaxoSmithKline. The other researchers report no relevant financial disclosures.
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