Infants under 1 year old often are assumed to be immune to measles, at least temporarily, thanks to maternal antibodies transferred during pregnancy. However, new research in the December 2019 Pediatrics suggests that this shared immunity may actually wane by 3 months of age. For the study, "Measles Antibody Levels in Young Infants" (published online Nov. 21), researchers with the analyzed measles antibody levels in blood serum samples collected from 196 infants under 12 months at the Hospital for Sick Children (SickKids) in Toronto, Canada. Among 1-month-old infants, they found that 20% had antibody levels that were below the protective threshold. Among those 3 months of age, 92% were below this threshold. In fact, all the infants lacked sufficient measles immunity by 6 months of age, based on antibody levels. According to the researchers, the assumed length of time that measles maternal antibody can protect infants is often based on studies performed where measles is endemic. Pregnant women who are immune to measles through immunization may not have the same level of antibodies as women who are immune through previous infection. Furthermore, in settings where measles does not circulate endemically, immunity is not routinely boosted. All of this can result in lower antibody levels transferred during pregnancy, which can leave infants susceptible to measles for much of their first year of life until they receive their first dose of vaccine, the authors say. In many countries, including the United States and Canada, the vaccine is routinely given starting at 12 months of age, based on the risk of measles infection and the ability of an infant's immune system to respond to the vaccine. The authors say current findings emphasize the critical importance of adequate community-wide immunization to protect vulnerable infants from measles, which can cause severe complications including pneumonia, encephalitis and death. The study was co-led by SickKids and Public Health Ontario.
The American Academy of Pediatrics is an organization of 67,000 primary care pediatricians, pediatric medical subspecialists and pediatric surgical specialists dedicated to the health, safety and well-being of infants, children, adolescents and young adults.