Repeat immunization with inactivated influenza vaccine appears to reduce children’s antibody responses to influenza strains A(H1N1)pdm09 and B, according to findings published in the Journal of the Pediatric Infectious Diseases Society. The effect of previous-season vaccination on the efficacy of live-attenuated influenza vaccine was less clear, researchers said.

Previous research has shown waning protection from influenza vaccine in patients who had been vaccinated during the previous season, but findings recently published in Annals of Family Medicine showed that repeat immunization with IIV appeared to increase long-term protection against some respiratory illness episodes in children with pre-existing medical conditions.