Background: Highly pathogenic avian influenza virus (HPAIV) infection has a high mortality rate in humans. Secondary bacterial pneumonia with HPAIV infection has not been reported in human patients, whereas seasonal influenza viruses sometimes enhance bacterial pneumonia, resulting in substantial morbidity and mortality. Therefore, if HPAIV infection were accompanied by bacterial infection, an increase in mortality would be expected. We examined whether a vaccine against HPAIV prevents severe morbidity caused by mixed infection with HPAIV and bacteria.
Methods: H7N7 subtype of HPAIV and Streptococcus pneumoniae were inoculated into cynomolgus macaques with or without vaccination of inactivated whole virus particles.
Results: Vaccination against H7N7 HPAIV decreased morbidity caused by HPAIV and pneumonia caused by S. pneumoniae. Bacterial replication in lungs was decreased by vaccination against HPAIV, although the reduction in bacterial colonies was not significant.
Conclusions: Vaccination against HPAIV reduces pneumonia caused by bacterial superinfection and may improve prognosis of HPAIV-infected patients.