Influenza Vaccine Given To Pregnant Women Reduces Hospitalization Due To Influenza In Their Infants

Isaac Benowitz, Yale School of Medicine


The aim of this study was to determine whether giving influenza vaccine to pregnant women can reduce the incidence of hospitalization due to influenza in their infants in the first year of life. This was a matched, hospital-based case-control study at Yale-New Haven Children's Hospital. Case and control subjects were all aged <12 months at the time of their hospital admission from 2000 to 2009. All subjects were identified through hospital records. Cases were infants admitted due to influenza infection. Controls were infants who did not have influenza infection at the time of>hospitalization, matched to cases by date of birth and date of hospitalization (both within 4 weeks before or after). We contacted parents of all subjects to collect information on the subjects' health and home setting and to get permission to review subjects' and mothers' hospital records and outpatient medical records--this was used to determine whether the subject or mother had received influenza vaccine or other vaccines and to identify underlying health conditions that could predispose to severe influenza infection. Conditional logistic regression was used to determine the relative risk of hospitalization for influenza infection for mothers who did or did not receive influenza vaccine during pregnancy or other times. The mothers of 2 (2.2%) of 91 cases and 31 (19.9%) of 156 controls aged <6 months and 1>(4.6%) of 22 cases and 2 (5.6%) of 36 controls aged ≥6 months received influenza vaccine during pregnancy. The effectiveness of influenza vaccine given to mothers in pregnancy in preventing hospitalization in their infants aged <6 >months, adjusted for potential confounders, was 91.5% (95% CI: 61.7%-98.1%, p=0.001). Influenza vaccine given to pregnant women was 91.5% effective in preventing hospitalization of their infants due to influenza in the first six months of life.