Measles Vaccine: Lower Seizure Risk When Given Early On

Diedtra Henderson

October 14, 2013

Infants who received vaccines containing live, attenuated measles were less likely to suffer a seizure within 7 to 10 days if the vaccination was administered at the recommended time, between 12 and 15 months of age, compared with older infants whose first measles dose was delayed, according to a large retrospective cohort study.

Ali Rowhani-Rahbar, MD, MPH, PhD, from the Kaiser Permanente Vaccine Study Center, Oakland, California, and coauthors published their results online October 14 in JAMA Pediatrics.

Two US Food and Drug Administration–approved vaccines containing live attenuated measles are administered to American children: the measles, mumps, and rubella vaccine and the measles, mumps, rubella, and varicella vaccine. The first shot of the 2-dose series is recommended to be given to infants between 12 and 15 months of age. Approximately 85% of infants receive the vaccination by age 19 months.

To examine the effect of infant age on the risk for vaccine-related fever and seizures, the researchers tapped the Vaccine Safety Datalink, a collaborative effort between the Centers for Disease Control and Prevention (CDC) and 10 managed care organizations. The database pools information on more than 9 million members and is used to track vaccine safety in the United States. The authors focused on the records of children aged between 12 and 23 months who had received measles-containing vaccine between January 2001 and December 2011, including 840,348 infants.

"We found that the magnitude of increased risk of seizures following immunization with measles-containing vaccines during the second year of life depends on age," Dr. Rowhani-Rahbar and colleagues write. "While measles-containing vaccines administered at 12 to 15 months of age are associated with an increased risk of seizures 7 to 10 days following immunization [relative risk, 3.4 (95% confidence interval [CI], 3.0 - 3.9); attributable risk, 4.0 excess cases per 10,000 doses (95% CI, 3.4 - 4.6)], their delayed administration at 16 to 23 months of age may result in an even greater increased risk of that adverse event following immunization [relative risk, 6.5 (95% CI, 5.3 - 8.1); attributable risk, 9.5 excess cases per 10,000 doses (95% CI, 7.6 - 11.5)]."

In an accompanying editorial, Kristen A. Feemster, MD, MPH, MSHPR, and Paul Offit, MD, both from the Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, and the Division of Infectious Diseases and the Vaccine Education Center, The Children's Hospital of Philadelphia, called the study "significant."

"First, it reinforces the well-established safety of the current recommended schedule, which is based on many years of prelicensure and postlicensure safety and effectiveness data, including concomitant use studies," Dr. Feemster and Dr. Offit write.

"Second, this study provides an example of the potential for current vaccine safety surveillance mechanisms to identify outcomes associated with alternate vaccine schedules."

Dr. Rowhani-Rahbar and colleagues note that a possible reason for the differing risk profiles is the ability of immune systems of 16- to 23-month-olds to mount a more rigorous response to the measles vaccine, compared with younger infants.

"Vaccines are typically recommended at an age that maximizes the likelihood of vaccine-induced protection and minimizes the risk of morbidity and mortality that would occur by delaying immunization. The safety profile of vaccines at different ages is another important consideration in immunization policy decision making," the authors conclude.

Support for this study was provided by the CDC. Nine of the 13 study authors disclosed receiving institutional research support from the CDC, and 1 study author disclosed being employed by the CDC. In addition, 1 coauthor disclosed receiving institutional research support from GlaxoSmithKline, 1 coauthor disclosed receiving institutional research support from MedImmune, 1 coauthor disclosed receiving institutional research support from Merck & Co; 1 coauthor disclosed receiving institutional research support from the National Institutes of Health, Novartis, Pfizer, and sanofi-pasteur; and 2 coauthors disclosed receiving institutional research support from Merck & Co, Novartis, GlaxoSmithKline, Pfizer, and sanofi-pasteur. The remaining authors and editorialists have disclosed no relevant financial relationships.

JAMA Pediatr. Published online October 14, 2013. Abstract