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What Clinicians Need to Know About MMRV Vaccine Safety

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) play a critical role in assuring vaccine safety in the United States. On February 27, 2008, information was presented to CDC's Advisory Committee on Immunization Practices (ACIP) on the risk of febrile seizures after measles, mumps, rubella, and varicella (MMRV vaccine: ProQuad®) vaccination. The ACIP updated recommendations to remove its previous preference for administering combination MMRV vaccine over separate injections of measles, mumps, and rubella (MMR) vaccine and varicella vaccine. These recommendations were released on March 13, 2008 in CDC's Morbidity and Mortality Weekly Report (MMWR). This safety update provides information for health care providers about the risk of febrile seizures after MMRV vaccine, ongoing CDC and FDA MMRV vaccine safety activities, and clinical guidance for use of MMRV vaccine.

Provider Summary

As part of routine safety monitoring for new vaccines, in 2007 CDC implemented a postlicensure vaccine safety study for the combined MMRV vaccine in children aged 12–23 months, the age when the first dose of MMRV or MMR and varicella vaccines is recommended.

Preliminary results from CDC's MMRV vaccine safety study among children aged 12–23 months found—

  • The rate of febrile seizures during the 7–10 days after vaccination was about 2 times higher in children who received MMRV vaccine (9 per 10,000 children vaccinated), compared with children who received measles, mumps, and rubella (MMR) and varicella vaccines separately at the same visit (4 per 10,000 children vaccinated).


  • During the 7–10 days after vaccination, about one additional febrile seizure would be expected to occur among every 2,000 children vaccinated with MMRV vaccine, compared with children vaccinated with MMR and varicella vaccine administered at the same visit.

CDC, FDA, and ACIP continue to evaluate these preliminary findings and other relevant data. They will communicate updates and take any further necessary actions based on this evaluation.

Clinical Guidance for Using the MMRV Vaccine

Clinical guidance for using the MMRV vaccine at this time includes—

  • MMRV vaccine is currently in very limited distribution in the United States, due to manufacturing issues unrelated to vaccine safety or efficacy. MMRV vaccine is not expected to be widely available before 2009; however, some clinics may have MMRV vaccine in stock.


  • ACIP continues to recommend two doses of vaccines to protect against measles, mumps, rubella, and varicella. The first dose is recommended at age 12–15 months, and the second dose is recommended at ages 4–6 years.


  • ACIP voted to change the preference language for MMRV vaccine to read as follows: "Combination MMRV vaccine is approved for use among healthy children aged 12 months–12 years. MMRV vaccine is indicated for simultaneous vaccination against measles, mumps, rubella, and varicella. ACIP does not express a preference for use of MMRV vaccine over separate injections of equivalent component vaccine (i.e., MMR vaccine and varicella vaccine)." ACIP recommendations are published in CDC's MMWR.


  • Providers can choose whether to administer combination MMRV vaccine or MMR and varicella vaccines separately for prevention of measles, mumps, rubella, and varicella.


  • Health care providers can remind parents that most children who receive an MMRV vaccine do not have any problems, and being vaccinated with MMRV or MMR and varicella vaccines is safer than getting measles, mumps, rubella, or chickenpox.


  • The second dose of MMRV or MMR and varicella vaccines is recommended at age 4–6 years. It is not known whether the risk of febrile seizures is higher in children aged 4–6 years who receive an MMRV vaccine, compared with separate MMR and varicella vaccines at the same visit. However, it is known that the second dose of MMR or MMRV vaccine is less likely to cause fever than the first dose, and rates of febrile seizures are lower in the general population of children aged 4–6 years than in children aged 12–15 months.


  • ACIP recommends that a personal or family history of seizures is not a contraindication or precaution for administration of MMRV, MMR, or varicella vaccines.


  • In February 2008, the MMRV package insert was updated based on FDA's review of postmarketing data. The revised package insert includes new and evolving information on the risk of febrile seizures after MMRV vaccination.


  • Febrile seizures generally have an excellent prognosis. The peak age for febrile seizures is 14–18 months, which overlaps with the ages when first doses of MMR and varicella vaccines are recommended.


  • CDC's Vaccine Information Statements were updated to be consistent with the MMRV package insert and to include new information on the risk of febrile seizures after MMRV vaccination.


  • Clinically significant adverse events that follow immunization should be reported to the Vaccine Adverse Event Reporting System (VAERS). A VAERS form is available online or by telephone at (800) 822-7967.

Other Studies

Results of other studies that are consistent with the preliminary results of the CDC study include—

  • In prelicensure studies of MMRV vaccine in children aged 12–23 months, rates of fever during 5–12 days after vaccination were higher in children who received an MMRV vaccine compared with children who received separate MMR and varicella vaccines at the same visit. Because certain children are prone to seizures when they have fever, finding an increased risk for febrile seizures at any time when fever is likely to occur makes sense.


  • Interim results from an ongoing Merck postlicensure study of children aged 12–60 months (99% of the children were aged 12–23 months) were presented at the February 2008 ACIP meeting. The study found that during 5–12 days after vaccination, the rate of febrile seizures was higher in children who received MMRV vaccine compared with children who received MMR and varicella vaccines at the same visit; the results were not statistically significant (MMRV vaccine: 5 per 10,000 children vaccinated; MMR and varicella vaccine: 2 per 10,000 children vaccinated). The rates of febrile seizures during the 0–30 days after vaccination were similar (MMRV vaccine: 10 per 10,000; MMR and varicella vaccine: 13 per 10,000).


  • A risk of febrile seizures after MMR vaccination has been documented. About one additional febrile seizure occurs for every 3,000–4,000 children who receive an MMR vaccine during 8–14 days after vaccination, compared with children who did not receive a vaccine during the past 30 days.

Additional Information about the MMRV Safety Study

Methods

Through use of CDC's Vaccine Safety Datalink (VSD) Project's rapid cycle analysis (RCA), scientists can detect vaccine adverse events in near real time. VSD uses administrative, computerized data from managed care organizations.

  • The study assessed risk for certain outcomes, including seizures, during the 0–42 days after vaccination in children aged 12–23 months who received an MMRV vaccine. The first dose of MMRV or MMR and varicella vaccines is recommended for this age group. Rates of certain adverse events in the MMRV vaccine group were compared with those among children who received MMR vaccine (many children also received varicella vaccine). Children in other age groups were not included in the study.


  • An elevated risk of seizures of any etiology was detected in the administrative data. The seizures were clustered around 7–10 days after vaccination with MMRV vaccine or MMR and varicella vaccines administered at the same visit.


  • Investigators reviewed the medical charts of children identified who had seizures 7–10 days after receiving an MMRV vaccine or MMR and varicella vaccines to distinguish febrile from afebrile seizures. Charts were not reviewed for children who had seizures during other time periods.


  • Investigators used epidemiologic methods to compare rates of febrile seizures among children in two study groups: 1) children who received an MMRV vaccine during January 2006 and August 2007, and 2) children who received MMR and varicella vaccines at the same visit during January 2000 and August 2007.

Preliminary Results

Preliminary findings from the study of MMRV vaccine and the risk of febrile seizures are described below. Only children aged 12–23 months were studied. This information was presented at the February 2008 ACIP meeting. CDC, FDA, and ACIP continue to evaluate this information.

  • Of the children identified in the administrative data as having seizures 7–10 days after vaccination, 90% were confirmed by chart review to have seizures. Of those, 95% were confirmed to be febrile seizures.


  • Of the 43,353 children who received an MMRV vaccine, 40 had febrile seizures 7–10 days after vaccination. Of the 314,599 who received MMR and varicella vaccines at the same visit, 128 had febrile seizures 7–10 days after vaccination. The rates of febrile seizures during 7–10 days after vaccination were about 9 per 10,000 in the MMRV vaccine group and about 4 per 10,000 in the MMR and varicella vaccine group.


  • The risk of febrile seizures during 7–10 days after vaccination was about 2 times higher in children who received an MMRV vaccine, compared with children who received MMR and varicella vaccines at the same visit.


  • During 7–10 days after vaccination, about one additional febrile seizure would be expected to occur for every 2,000 children who receive an MMRV vaccine, compared with children vaccinated with MMR and varicella vaccines at the same visit.


  • In the chart review of the children with febrile seizures 7–10 days after vaccination, hospitalization information was available for 166 children. Twenty-six (16%) were hospitalized for febrile seizures, and no child who had a febrile seizure died.


  • A similar percentage of children with febrile seizures in the MMRV vaccine group (29%) and the MMR and varicella vaccines group (31%) had a history of seizures.

Additional Resources

For more information about this study, please visit:

To learn more about MMRV vaccine, febrile seizures, and vaccine safety, visit the following sites:

PDF IconPlease note: Some of these publications are available for download only as Portable Document Format (PDF) files, which require Adobe® Acrobat® Reader to view. Please review the information on downloading and using Acrobat Reader software.

*Links to non-Federal organizations found at this site are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links.

Page last modified: April 29, 2008
Content source: Immunization Safety Office

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