Influenza: Annual seasonal severity

Purpose of reviewInfluenza remains a major cause of morbidity and mortality. The 2017-2018 season was one of the most severe in the past decade. The exact factors determining the severity of a particular influenza season are complex and often poorly understood.Recent findingsFactors impacting annual influenza severity include characteristics of the specific virus, influenza vaccination, and antiviral use. Although viral virulence factors are important in this context and our knowledge of these is growing, there is a complex interplay between expression of these factors and their impact on a particular patient population. Vaccination has demonstrated efficacy in preventing disease, but vaccination rates remain sub-optimal and vaccine effectiveness can vary significantly between influenza strains and patient populations. Finally, while antiviral treatment is available and has shown benefits, many patients with influenza do not receive treatment.SummaryStrides have been made in recent years towards understanding the many factors that contribute to the severity of any particular influenza season. Obvious areas for improvement include improved vaccination rates and antiviral use. Additionally, a more complete understanding of reasons for poor strain and population-specific vaccine effectiveness may help reduce the severity of future influenza seasons.