Maternal influenza vaccination may be associated with flu protection in infants

Young children are consistently at higher risk of complications from infection with the influenza virus, according to background information in the article. However, they are ineligible to be vaccinated until age 6 months. "Influenza virus infection in infants is generally more frequent among those aged 6 to 12 months than in the first six months of life, potentially owing to the protection conferred by maternal influenza antibodies acquired transplacentally or through breastfeeding," the authors write. "However, during severe influenza seasons, morbidity and mortality rates among infants younger than 6 months have been reported to exceed those of older infants."

Angelia A. Eick, Ph.D., then of Johns Hopkins Bloomberg School of Public Health, Baltimore, and now of the Armed Forces Health Surveillance Center, Silver Spring, Md., and colleagues conducted a non-randomized observational cohort study on Navajo and White Mountain Apache Indian reservations, where children have a higher rate of severe respiratory infection than the general population. A group of 1,169 women who delivered babies during one of three influenza seasons completed questionnaires about demographics, vaccination status of all family members and flu risk factors. A total of 1,160 mother-infant pairs then gave blood samples that were assessed for flu antibody presence. Mothers completed a second questionnaire at the end of the flu season and surveillance was conducted throughout to track new influenza-like illnesses.

During the flu season following their birth, 193 (17 percent) of infants were hospitalized for influenza-like illness, 412 (36 percent) had only an outpatient visit for a respiratory cause and 555 (48 percent) had no flu- or flu-like episodes. Infants whose mothers were vaccinated had a 41 percent lower risk of laboratory-confirmed influenza virus infection and a 39 percent reduced risk of hospitalization from influenza-like illness. In addition, those with blood samples available had higher levels of flu antibodies at birth and at 2 to 3 months than babies born to unvaccinated women.

"Although influenza vaccination is recommended for pregnant women to reduce their risk of influenza complications, these findings provide support for the added benefit of protecting infants from influenza virus infection up to six months, the period when infants are not eligible for influenza vaccination but are at highest risk of severe influenza illness," they conclude. "These findings are particularly relevant with the emergence of 2009 pandemic influenza A (H1N1) virus, which had a substantial impact on pregnant women and high hospitalization rates among young infants."

The study was funded by the National Vaccine Program Office, Department of Health and Human Services, the Office of Minority Women's Health, Centers for Disease Control and Prevention, Aventis-Pasteur and Evans-Powderject. 

Editorial: Maternal Vaccine Promising for Preventing Flu in Infants

"The burden of influenza among pregnant women, the excellent safety profile of the vaccine and the reliable immunogenicity of trivalent inactivated influenza vaccine in this group support a recommendation that all pregnant women receive influenza vaccine to decrease complications of influenza disease during their pregnancies," write Justin R. Ortiz, M.D., and Kathleen M. Neuzil, M.D., M.P.H., of PATH and the University of Washington, Seattle, in an accompanying editorial.

"While the burden of influenza is not as well characterized in many tropical and developing countries, available evidence, including evidence from the recent H1N1 pandemic, supports that pregnant women are at high risk for influenza-related morbidity," they continue.

"The additional benefits of maternal influenza vaccination to the newborn, as demonstrated in the Bangladesh and White Mountain and Apache Navajo communities, should catalyze efforts to improve vaccination rates in countries with existing maternal immunization recommendations," they conclude. "Likewise, these data should encourage the adoption of vaccination guidelines in countries without such recommendations. Maternal influenza vaccination targets two high-risk groups with one vaccine dose -- we can't afford not to act."