Vaccinating Pregnant Women Fights Flu in Infants

Vaccinating pregnant women against influenza is over 90% effective in preventing their infants from being hospitalized with influenza in the first six months of life, according to a three-year study by Yale School of Medicine researchers.

The study, which is published Clinical Infectious Diseases, builds on preliminary data the research team presented last year at the Infectious Disease Society of America in Philadelphia.

Infants under the age of one year are at high risk of hospitalization for influenza. However, despite the fact that the flu vaccine is recommended for all pregnant women and children, no vaccine is currently approved for infants less than six months of age.

“Effective approaches are needed to protect this vulnerable population,” wrote the authors, who set out to examined the effectiveness of vaccinating women during pregnancy—a strategy that might “protect the infant through transfer of antibodies from the mother”—in preventing hospitalization in infants.

For the study, Isaac Benowitz and colleagues enrolled infants hospitalized at Yale-New Haven Hospital due to influenza and a similar group of infants without influenza. The researchers then compared whether each infant's mother had gotten the flu vaccine during pregnancy.

They found that the mothers of two (2.2%) of 91 case subjects and 31 (19.9%) of 156 control subjects aged ≤6 months, and one (4.6%) of 22 case subjects and two (5.6%) of 36 control subjects aged >6 months, had received influenza vaccine during pregnancy. The effectiveness of influenza vaccine given to mothers during pregnancy in preventing hospitalization among their infants, adjusted for potential confounders, was 91.5% for infants aged <6 months.

"When we compared vaccination rates during pregnancy in the study, we found that in the group of infants who didn't have influenza, far more mothers received the influenza vaccine," said Vazquez, assistant professor in the department of pediatrics at Yale, in an online report.

Vazquez said that the study's findings provide an effective strategy for protecting infants under six months old, for whom no vaccine is available. She also points out that vaccination during pregnancy is cost-effective, as one vaccine protects two individuals.

For more:

• Influenza Vaccine Given to Pregnant Women Reduces Hospitalization Due to Influenza in Their Infants (Clinical Infectious Diseases)
• Helping Mothers Prevent Influenza Illness in Their Infants (Pediatrics)
• Docs Urged to Immunize Pregnant, Postpartum Women against Influenza (HCPLive)