Effectiveness of pneumococcal conjugate vaccine in infants by maternal influenza vaccination status.

ABSTRACT

BACKGROUND: Influenza virus infection can predispose patients to secondary pneumococcal infections. Children are at greatest risk for pneumococcal infection in the first year of life and are not considered fully protected by pneumococcal conjugate vaccine (PCV) until their third dose at 6 months of age. Infants less than 6 months cannot receive influenza vaccination, though maternal influenza vaccination can protect infants. METHODS: We conducted a retrospective cohort study of 9807 mother-infant pairs enrolled in a managed care organization for infants born June 1, 2002, to December 31, 2009. Exposure was assessed for receipt of infant PCV only and the combination of PCV and maternal influenza vaccine (trivalent inactivated vaccine). Outcomes of interest were acute otitis media and medically attended acute respiratory infection in the first year of life. We estimated the adjusted incidence of illness, incidence rate ratios and vaccine effectiveness using the ratio of incidence rate ratios between the periods of noncirculating influenza and that of at least local influenza circulation. RESULTS: For medically attended acute respiratory infection, vaccine effectiveness for the combination of trivalent inactivated vaccine and PCV was 39.6% (95% confidence interval [CI] 31.6%-46.7%) and for PCV only was 29.8% (95% CI 11.4%-44.3%). For acute otitis media, vaccine effectiveness for the combination of trivalent inactivated vaccine and PCV was 47.9% (95% CI 42%-53.3%) and for PCV only was 37.6% (95% CI 23.1%-49.4%). CONCLUSION: In infants, the combination of maternal influenza vaccine and infant pneumococcal conjugate vaccination confers greater protection from acute otitis media infections and medically attended acute respiratory infections than does PCV alone.