The Combination Measles-Mumps-Rubella-Varicella (MMRV) Vaccine Is Associated with Increased Seizure Risk in Toddlers

According to a recent study of more than 700,000 12-23 month old children, the combination measles-mumps-rubella-varicella (MMRV) vaccine is associated with an increased risk of seizures seven to 10 days after vaccination, compared to the separately administered MMR and varicella (MMR+V) vaccine.

These results were presented on October 3, 2013, by Nicola P. Klein, MD, PhD, a research scientist at the Kaiser Permanente Vaccine Study Center in Oakland, CA, and her colleagues at IDWeek 2013, a joint meeting of the Infectious Diseases Society of America (IDSA), the Society for Healthcare Epidemiology of America (SHEA), the HIV Medicine Association (HIVMA), and the Pediatric Infectious Diseases Society (PIDS), in San Francisco, CA.

Measles-containing vaccines increase the risk of seizure and fever within the seven to 10-day post-vaccine period in toddlers, according to previous research. Additionally, administering varicella in combination with the measles vaccine may also have a greater effect on health outcomes, although the mechanisms for this are not clear. The present study assessed the relative risk of seven other pre-specified health outcomes, in addition to seizure and fever, in 12-23 month old children between 2000-2012 who were part of the Vaccine Safety Datalink and had received the MMRV or the MMR+V vaccine.

The primary analysis compared MMRV with MMR+V in terms of the post-vaccination outcome risk over a defined time interval. This time interval corresponded approximately with when the vaccination-related outcome was predicted to occur. Overall, the risk of any outcome occurring was not different between the MMRV and MMR+V. However, several of these outcomes, such as arthritis, Kawasaki Disease, anaphylaxis, and encephalitis/meningitis, had few to no cases associated with them. According to Klein, a greater number of cases in future analyses will better assess possible differences in the outcomes between MMRV and MMR+V vaccines.

The researchers then analyzed the data by comparing the risk of a post-vaccination outcome within the defined time interval they used in the primary analysis with the risk of an outcome in a later time interval (termed the “control interval”). Both the MMRV and the MMR+V vaccines were associated with a greater incidence of fever, seizures, and immune thrombocytopenia purpura (ITP) seven to 10 days after vaccine administration. Although the incidence of fever and ITP did not differ between the two groups, the MMRV had a greater risk of seizures within that time period compared with the MMR+V.

Anaphylaxis was more likely to occur immediately after MMRV vaccination, whereas ataxia was significantly less likely to occur within the 42 days following both vaccinations. However, the small number of anaphylaxis and ataxia cases limits the extent to which they can be applied to the general and should be investigated in future research, according to Klein.

All authors listed financial disclosures.