Viral Respiratory Infections: Influenza

The influenza virus is a highly contagious respiratory pathogen that causes yearly seasonal epidemics and occasional pandemics, leading to significant health and economic consequences. It spreads through droplets, aerosols, and surfaces. Infected individuals are contagious before symptoms appear, with peak infectivity early in the illness. In the United States, the 2024-2025 influenza season was the most severe since 2017-2018, with an estimated 47 to 82 million cases, up to 1.3 million hospitalizations, and up to 130,000 deaths. The risk of adverse outcomes is higher for vulnerable groups, including older adults, infants, and individuals who are immunocompromised, those with chronic conditions, and individuals who are pregnant, long-term care facility residents, and individuals experiencing homelessness. Vaccination is the main preventive measure and is recommended for all patients 6 months and older unless contraindicated. Advances in vaccines have improved efficacy. For the 2024-2025 vaccine, efficacy ranged from 32% to 78%, depending on age group and outcome. Misinformation, limited access, mistrust, and disparities are barriers to administration. Antiviral medications including oseltamivir and zanamivir can reduce illness and complications if given early in the infection course, and new therapies are being developed for drug-resistant strains. Strategies to more effectively address influenza include improving access to vaccines, countering misinformation, performing community outreach, and advancing research on antiviral medications and universal vaccines.