Abstract
We used RT-PCR-electrospray ionization-mass spectrometry to identify subtypes and strains of influenza viruses detected during a maternal influenza immunization study in Nepal from May 2011 to April 2014. Hemagglutinin (HA) gene amino acid (aa) sequences of inferred reference strains were compared to those of the vaccines to determine impact of aa relatedness on vaccine efficacy (VE) and disease severity. Three influenza subtypes and many strains were identified. A(H3N2) strains with less than 13 aa differences in HA compared to vaccine strains (matched) showed higher VE than strains with 13 or more differences (mismatched). Yamagata lineage B strains, which were mismatched to the Victoria strain in the vaccine, demonstrated lower VE compared to Victoria strains. Differences in VE were not statistically significant. All A(H1N1pdm) matched the vaccine strain, with 10 or fewer aa differences. Except for women infected with vaccine-matched strains of influenza A, clinical signs and symptoms did not differ between vaccinated and unvaccinated participants.