Infants may be susceptible to measles for months before they are vaccinated.
A new study found protection infants receive from maternal antibodies is short-lived.
“Therefore, the best strategy for protecting infants against measles is adequate community protection, delivered through high coverage of 2 doses of measles-containing vaccine,” authors wrote in “Measles Antibody Levels in Young Infants,” (Science M, et al. Pediatrics. Nov. 21, 2019, https://doi.org/10.1542/peds.2019-0630).
The Centers for Disease Control and Prevention (CDC) and the Academy recommend children receive the first routine dose of measles, mumps and rubella (MMR) vaccine at 12-15 months and the second dose at 4-6 years.
Mothers can transfer these antibodies to their children in utero, and it has been assumed that infants are protected throughout the first year of life. This notion, however, “was based on studies performed in settings where measles circulated endemically,” according to the study.
The authors of this study aimed to look at whether mothers who were vaccinated against measles and live in areas where measles has been eliminated pass on less protection than mothers who were infected with the virus and were exposed to circulating measles.
The team used a plaque reduction neutralization test to analyze blood serum from 196 infants under 1 year in Toronto, Canada, where measles has been eliminated since 1998. Those with a neutralization titer of less than 192 milli-international units per milliliter were considered susceptible. Infants with immune deficiency conditions were excluded.
- 20% were not immune at 0 months,
- 32% were not immune at 1 month,
- 67% were not immune at 2 months,
- 92% were not immune at 3 and 4 months, and
- 100% were not immune at 6-11 months.
Those with an underlying condition were more likely to be susceptible. The difference between those who did and did not receive any breastmilk was not statistically significant. Older mothers were linked to somewhat higher infant susceptibility.
“The widening gap between loss of maternal antibodies and measles vaccination described in our study leaves infants vulnerable to measles for much of their infancy and highlights the need for further research to support public health policy,” authors wrote.
Like the U.S., Canada recommends children receive the first dose of MMR vaccine at 12-15 months. Authors noted giving the vaccine to infants earlier could limit its effectiveness, and giving it to women during pregnancy is not an option because it is a live attenuated vaccine. They stressed the need for high vaccination rates in the community to protect vulnerable infants.
The study comes on the heels of the U.S. nearly losing its elimination status earlier this year. There have been 1,261 cases in 31 states this year, the most since 1992 and since measles was eliminated in 2000. Outbreaks in New York ended just before reaching the one-year mark.
Authors of a related commentary including former CDC Advisory Committee on Immunization Practices member Walter A. Orenstein, M.D., FAAP, noted with the exception of this year and 2014, measles cases typically are low and less than 15% impact infants. In addition, infants can be vaccinated early if they are in an outbreak area. They echoed the call for increasing community immunity instead of lowering the vaccination age.
“In the era of elimination, high coverage of 2 doses of MMR becomes essential to reduce the risk of exposure to infection and protect infants who cannot be vaccinated,” they wrote.
The AAP has been working to improve vaccination rates by advocating for the elimination of nonmedical exemptions to school vaccine requirements and partnering with social media networks like Pinterest to make sure parents using their platforms are seeing credible, science-based information.