How Long Does Maternal Influenza Immunization Protect Infants?
Maternal immunization against influenza protects infants for a short amount of time, but the protection rapidly decreases with age. Researchers reported their findings in the journal Pediatrics.
Investigators followed up with infants of women who were participants in a randomized, double-blind, placebo-controlled trial of the trivalent inactivated influenza vaccine (IIV3) during pregnancy. The trial occurred in 2011 and 2012 and involved 1,026 infants whose mothers received the vaccine and 1,023 infants whose mothers received a placebo. Infants were followed up during the first 6 months of life for influenza illness, and a secondary subset of infants underwent assessment of hemagglutination inhibition (HAI) antibodies.
The IIV3 maternal vaccine was most efficacious in protecting infants 8 weeks of age or younger (85.6%) from influenza, but those benefits quickly diminished. In infants 8 to 16 weeks of age, the efficacy of the maternal vaccine was 25.5%, and among infants 16 to 24 weeks of age the efficacy of the vaccine was 30.3%.
HAI titers reflected a similar trend. In mothers receiving the IIV3 vaccine, 56% of infants in the first week of life had titers of 1:40 or more to the influenza vaccine strains, compared with less than 40% of infants at 16 weeks of age and less than 10% of infants at 24 weeks of age.
“Maternal immunization conferred protection against infection in the infants for a limited period during early life. The lack of protection beyond 8 weeks of age correlated with a decrease in maternally derived antibodies,” the study’s authors concluded.
In an accompanying editorial, Flor M. Munoz, MD, emphasized the need for more immunogenic vaccines. "If more immunogenic vaccines were administered to pregnant mothers, infants would benefit from more robust and longer lasting protection in the first few months of life," she wrote. In the meantime, she stated that “it is imperative that passive protection is optimized.”
—Lauren LeBano
References
1. Nunes MC, Cutland CL, Jones S, et al. Duration of infant protection against influenza illness conferred by maternal immunization. JAMA Pediatr. 2016 Jul 5. doi: 10.1001/jamapediatrics.2016.0921. [Epub ahead of print].
2. Munoz FM. Infant protection against influenza through maternal immunization: A call for more immunogenic vaccines. JAMA Pediatr. 2016 Jul 5. doi: 10.1001/jamapediatrics.2016.1322. [Epub ahead of print].