MMR and Chickenpox Vaccines and the Risk of Seizures

Keris Krennhrubec, Amelia Murphy, and Diana Zuckerman, PhD, National Center for Health Research

The combination measles, mumps, rubella, and chickenpox (also called varicella) vaccine is convenient for parents and young children: four vaccines in only one shot. But research shows that this combination vaccine may increase the risk of fever-related seizures in children compared to having the separate MMR and chickenpox vaccines at the same time. Parents are asking: What does this mean for me and my child? Is the vaccine still safe to get? If my child has already had the vaccine, do I need to worry about any risks?

MMRV Vaccine (ProQuad)

Most young children in the United States get a combination vaccine against the measles, mumps, and rubella-known as the MMR vaccine. This has been a routine vaccine for young children since the 1970s. These three diseases used to be common, but since this vaccine was developed they have been almost eradicated in the U.S.[1] In 1995, a vaccine was developed for another routine childhood disease: chickenpox (varicella). Since children need to get all four of these vaccines, Merck (the company that makes both of them) decided to combine them all into one, called the MMRV vaccine (for measles, mumps, rubella, and varicella), or ProQuad. The Food and Drug Administration (FDA) approved this combination vaccine in 2005, and soon afterwards parents started choosing it for their children, thinking that fewer shots would be better.

At the time of FDA approval, there was evidence of a slightly increased risk of fever-related seizures among children who got the vaccine, but the vaccine was approved with a commitment from Merck to do a large post-marketing study to further understand this risk. Now, these studies are showing that children ages 12-23 months who get this vaccine are twice as likely to have seizures caused by high fevers compared to toddlers of the same age who get the MMR and chickenpox vaccines separately but at the same doctor visit. There is no excess risk of seizures for children getting vaccinated with MMRV at ages 4 to 6 years.[2]

Fevers and Seizures

All small children are at risk for seizures if they have a high fever, with the risk peaking when a child is between 14 and 18 months old.[3] This risk is increased slightly after receiving either the MMR vaccine or the chickenpox vaccine. Approximately 3 in 10,000 children will have seizures after getting the MMR vaccine,[1] and that increases to about 4 in 10,000 if they get the separate chickenpox vaccine at the same doctor visit.  Unfortunately, the rate of seizures goes up to 9 per 10,000 children who get ProQuad (combined MMR/chickenpox vaccine).  These results were reported at the 2008 meeting of the CDC Authorization Committee on Immunization Practices (ACIP), based on a study of 43,000 children who got ProQuad and 315,000 children who got the MMR and separate chickenpox vaccine, by Dr. Nicola Klein at the Kaiser Permanente Vaccine Study Center. No children died, and no children experienced any long-term problems.[4]

A more recent study in Canada, reported in June 2014, confirmed these findings. Researchers looked at data for 277,774 children aged 12-23 months for 7-10 days after their vaccinations.  Like Dr. Klein, they also reported that the seizure rate was more than twice as high with the MMRV vaccine. Among those vaccinated with MMRV, 5.8 out of 10,000 participants experienced seizures, whereas among those vaccinated with the MMR and chickenpox vaccines separately, 2.2 out of 10,000 participants experienced seizures.[5]

Merck and ProQuad

Originally, the CDC recommended vaccinating children with ProQuad instead of the two separate vaccines. However, due to the data on seizure risk, the CDC changed its recommendation and now says that the combination vaccine is no better, and is not always preferred. Merck has also reported findings in their own research that the combination vaccine results in more seizures. They agree with Dr. Klein that the risk of seizure doubles in the first 5 to 12 days after vaccination.[4]

What Are the Current Recommendations?

In June 2009, the ACIP adopted new recommendations concerning use of the MMRV vaccine, for the first and second doses. The CDC then released new recommendations on the use of the vaccine in May 2010. According to the CDC, the recommendations have not changed since then and are as follows: [6] [7]

  • For the first dose at age 12-47 months, either the MMR vaccine and varicella vaccine may be given in separate injections, or the MMRV vaccine may be used. Unless a parent expresses a preference for the MMRV vaccine, the CDC recommends that separate MMR and varicella vaccines should be administered for the first dose in this age group.
  • For the second dose at any age, and for the first dose in children ages 4 years or older, use of the MMRV vaccine is generally preferred over separate injections of the MMR vaccine and the varicella vaccine.
  • Children with a personal or family history of seizures generally should be vaccinated with the MMR vaccine and varicella vaccine separately (as opposed to the combined MMRV vaccine).

Which Vaccine Should My Child Get?

Getting the vaccines separately and getting the combination vaccine both cost about $150.[8] The ProQuad vaccine is still legal and approved by the FDA, and no children have died or become seriously ill because of their seizures. The FDA has updated the package insert of ProQuad to inform all health care providers and consumers about the seizure risks.[9] The probability of your child having convulsions is still relatively low, but the risk is lower for the two vaccines instead of the combination. Regardless of whether you choose to give your child the vaccines separately or in the combined MMRV, it is important to remember that it is safer for your child to get these vaccines than for them to get the diseases they protect against.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

  1. National Network for Immunization Information. Vaccine Information: Measles. Retrieved February 29, 2008. https://www.immunizationinfo.com/measles/
  2. Centers for Disease Control and Prevention. Measles, Mumps, Rubella, and Varicella (MMRV) Vaccine (2014, June 23). Retrieved from: http://www.cdc.gov/vaccinesafety/Vaccines/MMRV/Index.html
  3. Food and Drug Administration. (2009, November 3). Information Pertaining to Labeling Revision for ProQuad. Retrieved November 3, 2014 from: http://www.fda.gov/BiologicsBloodVaccines/Vaccines/ApprovedProducts/ucm123798.htm
  4. Centers for Disease Control and Prevention. (2008, February 27). What Clinicians Need to Know About MMRV Vaccine Safety. Retrieved February 29, 2008. https://www.cdc.gov/vaccinesafety/vsd/mmrv.htm
  5. MacDonald SE, Dover DC, Simmonds KA, Svenson LW. “Risk of febrile seizures after first dose of measles-mumps-rubella-varicella vaccine: a population-based cohort study.” Canadian Medical Association Journal. 2014; 186(11): 824-9
  6. Centers for Disease Control and Prevention. (updated 2014, March 12).Q&As About Vaccination Options for Preventing Measles, Mumps, Rubella, and Varicella. Retrieved November 3, 2014 from: http://www.cdc.gov/vaccines/vpd-vac/combo-vaccines/mmrv/vacopt-faqs-hcp.htm
  7. Centers for Disease Control and Prevention. (2013, June 18). MMRV (Measles, Mumps, Rubella & Varicella) Vaccine: What You Need to Know. Retrieved November 3, 2014 from: http://www.cdc.gov/vaccines/hcp/vis/vis-statements/mmrv.html
  8. Centers for Disease Control and Prevention. (updated 2014, August 1). Vaccines for Children Program (VFC). Retrieved November 4, 2014 from: http://www.cdc.gov/vaccines/programs/vfc/awardees/vaccine-management/price-list/
  9. Food and Drug Administration. (2009, November 3). Information Pertaining to Labeling Revision for ProQuad. Retrieved November 3, 2014 from: http://www.fda.gov/BiologicsBloodVaccines/Vaccines/ApprovedProducts/ucm123798.htm