Should Infants Under 9 Months of Age Be Vaccinated for Measles?

Researchers from the Office of Biostatistics and Epidemiology, as well as the Office of Vaccines Research and Review of the Center for Biologics Evaluation and Research, and the US Food and Drug Administration (FDA) have found that measles vaccines may be beneficial for infants under 9 months during a measles outbreak, according to a study recently published in The Pediatric Infectious Disease Journal.

Measles is highly contagious and continues to be a threat to public health around the world as it carries significant morbidity and mortality. According to the study, measles is “resurging, with more than 700 confirmed cases since January 2014.” Vaccination is the most effective means to prevent measles, thus, during measles outbreaks, it is sometimes recommended for infants to be vaccinated as early as 6 months old, due to the fact that they are more at risk. According to the study, “Death occurs in 1 to 3 per 1,000 cases of measles in the United States, with higher mortality in individuals younger than 5 years of age among immunocompromised children.”

The measles, mumps, and rubella (MMR) vaccine is used in the United States to protect individuals against measles. Currently, it is recommended by the US Advisory Committee on Immunization Practices that children receive their first dose of the combined MMR vaccine on or after their first birthday. However, according to the study, vaccination can be administered in infants of 6 months of age if there is a measles outbreak or if they will be traveling to a measles-endemic area. There have not been many trials conducted within the United States that have assessed the safety of administering the MMR vaccine to young infants, and with the resurgence of measles, vaccinating infants may become necessary.

The study researchers set out to learn more about the adverse event profile of MMR or measles, mumps, rubella, and varicella (MMRV) vaccines in infants younger than 9 months of age due to their susceptibility to infection. To effectively do this, the researchers searched the Vaccine Adverse Event Reporting System (VAERS), a national surveillance system of adverse events that occur after vaccination. VAERS is managed by the FDA as well as the Centers for Disease Control and Prevention (CDC) and receives over 30,000 reports annually. According to the press release, these reports are submitted by a wide range of people: from vaccine recipients to healthcare providers to vaccine manufacturers. The researchers searched VAERS for reports of adverse events in infants less than 9 months old that occurred after MMR or MMRV between 1990 and 2014.

Each report was reviwed for verification of age and identification of administered vaccines. The researchers then summarized the “frequency, range, onset time, and severity of adverse events, with particular attention to deaths and other serious adverse events.” Then, using the description in the report, they performed a clinical assessment. According to the researchers, “Our clinical assessment of each case was based on the narrative description of the event, vaccine(s) administered, time course, treatment, medical history, any available medical records, and information about other exposures.” In addition, the researchers made note of the reasons for early immunization of the infants.

A total of 550 reports were reviewed; however, 346 reports were omitted due to incorrect or insufficient information or if they were duplicated. Out of the 204 reports the researchers ended up using for their study, only 17%, or 35 reports noted adverse effects that were defined as serious. Nineteen of the 35 reports with adverse effects were reports on the MMR vaccine with 17 of them proving to be serious, and 16 of the 35 reports were MMRV reports, all of them deemed "nonserious." A total of 52%, or 88, of the other 169 "nonserious" reports noted vaccination errors (the reports used terms such as “wrong vaccine") but did not show any notable adverse events. The most common symptoms found in non-serious reports were reactions at the injection site, fever, or gastrointestinally-related. The serious adverse events reported included fussiness, fever, and autism, as well as other developmental disorders in the vaccinated infants. However, according to the press release, "In its review of the evidence and causality of adverse effects of vaccines, the Institute of Medicine concluded that the evidence favors rejection of a causal relationship between MMR vaccine and autism."

Based on the results of their study, the researchers concluded that after close inspection of the adverse events reported in VAERS, there are no major safety concerns for administering the MMR vaccine to infants under the age of 9 months. They hope that their findings will help prompt discussion among policy makers and clinicians of the benefits and risks of vaccinating infants during measles outbreaks.