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MMRV vaccine increased risk for febrile seizures
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Canadian children who received the combination measles-mumps-rubella-varicella vaccine were at twice the risk for febrile seizures compared with those who received separate measles-mumps-rubella and varicella vaccines, according to study results published in the Canadian Medical Association Journal.
However, the absolute risk among both groups was relatively low.
Previous research suggests that the MMRV vaccine has a similar safety profile to that of the coadministration of MMR and varicella vaccines and has the advantage of requiring fewer needles for children. Although febrile seizures do not have long-term health consequences, researchers are concerned the increased risk may undermine the benefits of the combination dose.
“Combining MMR and varicella into a single vaccine decreases pain for children and distress for parents, thus addressing common barriers to vaccine uptake, and may improve vaccination coverage levels and decrease immunization delivery costs,” Shannon E. MacDonald, PhD, RN, of the University of Calgary, Alberta, and colleagues wrote. “Febrile seizures are typically self-limiting and rarely have long-term effects, but they can be extremely distressing for parents, may precipitate acute care visits and may undermine confidence in immunization programs.”
Shannon E. MacDonald
The analysis included 227,774 children aged 12 to 23 months who received MMRV or the coadministration of MMR plus varicella vaccines between 2006 and 2012 in Alberta.
The combination MMRV vaccine (Priorix-Tetra, GlaxoSmithKline) was approved for use in Canada in 2007 and added to the routine childhood immunization schedule in 2010. It is a different formulation than the MMRV vaccine used in the United States (ProQuad, Merck).
MacDonald and colleagues observed an increase in seizures 7 to 10 days after either vaccine combination — what they called the “peak period” for seizure incidence. During this period, seizures were twice as common among children who received MMRV compared with those who received separate vaccinations (RR=1.99; 95% CI, 1.3-3.05). This translates to 3.52 seizures per 10,000 vaccine doses administered, or one excess seizure for every 2,841 doses.
The researchers noted that these findings are consistent with the results of a study of the MMRV vaccine used in the US. That study had prompted the Advisory Committee on Immunization Practices to reconsider its preference for the use of the combination vaccine for the first dose and advise that clinicians and parents should consider the risks of MMRV before making a choice.
Among high-risk children — those with a personal history of febrile seizure or seizure disorder, for example — the risk for seizures was not differentially elevated with MMRV (RR=1.3; 95% CI, 0.6-2.79), but among low-risk children, it was (RR=2.27; 95% CI, 1.48-3.49). The low risk for seizures among high-risk children may be explained by the high baseline incidence of seizures in this group. “The lack of a differentially increased risk after MMRV in the high-risk group is reassuring and suggests that no additional criteria are needed to guide immunization of this group,” the researchers wrote.
According to the MacDonald and colleagues, use of MMRV vaccine is a matter of weighing its benefits with the slight increase in risk for febrile seizures.
“Parents should be informed about the benefits and risks of the combination vaccine,” MacDonald told Infectious Disease News. “Namely, the trade-off between reducing the number of needles the child receives vs. the slightly increased (but still very small) risk of febrile seizures. A critical part of the message to parents is that, although MMRV vaccine has a slightly higher risk of febrile seizures compared to the previously separate vaccines, the risk of seizures is significantly higher if the child contracts measles disease (in fact, 10-fold higher). This is in addition to all the other risks from the diseases that the vaccine protects against.” – John Schoen
Disclosure: MacDonald reports no relevant financial disclosures.
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