Influenza Virus in Community-Acquired Pneumonia: Current Understanding and Knowledge Gaps

Influenza virus infection poses a heavy burden on global health and economics. With the advancement in viral pathogen detection methods, the role of virus infection in community-acquired pneumonia has been increasingly recognized. The disease spectrum of influenza ranges from asymptomatic infection to severe or even fatal illness. Progress has been made in recent years to identify risk factors including lymphopenia and hypoxia for influenza mortality. Immunopathology plays an important role in influenza pathogenesis. The disturbed homeostasis after virus infection consists of both an excessive inflammatory phase and an immune suppression phase, collectively described as viral sepsis. Multiple antiviral therapies have been tested and some were advanced to late-phase clinical trials, including polymerase inhibitors, hemagglutinin inhibitors, host-acting antivirals, monoclonal antibodies, and adjunctive immunomodulatory therapies. Combination therapies have been shown to increase antiviral efficacy and genetic resistance barrier. In this review, we summarized the recent advances in our understanding of the disease pathogenesis, as well as the progress in antiviral therapy development. We also pointed out current key knowledge gaps in influenza research. Hopefully, experience gained from seasonal influenza research will prepare us for the next influenza pandemic and emerging respiratory pathogens.