Influenza A Infections in Infants of Vaccinated and Unvaccinated Mothers

To the Editor We read with interest the article by Hviid et al¹ showing influenza A (H1N1) pdm09 vaccine to be safe for use during pregnancy. There has been a reduced risk for influenza and influenza-like illness observed among the infants of vaccinated mothers,² thought to be owing to transplacental transfer of maternal antibodies.³ Do the data allow comparison of influenza A infections in the offspring between the mothers who have been vaccinated and unvaccinated? This would be of interest because influenza infections are associated with excess morbidity including excess hospitalizations.⁴