Like the influenza viruses themselves, the burden of the influenza illness varies from year to year, depending on the circulating strains, the effectiveness of vaccines and treatment, and the particular vulnerabilities of different populations, such as the pediatric and elderly populations. Influenza vaccination is the best way to prevent influenza and the potentially serious related complications. In fact, it prevents millions of influenza illnesses and related doctor visits and tens of thousands of hospitalizations every year. It is important to note, however, that the influenza vaccine can vary in its overall and strain-specific effectiveness from year to year.

For instance, the 2017-2018 flu season had a high rate of influenza-like illness, reaching almost pandemic levels, as well as high levels of hospitalizations and mortality across all age groups. It was also an H3N2-predominant flu season, and, historically, H3N2-predominant seasons tend to be more severe. In the 2018-2019 season, influenza severity was classified as moderate, and the season was notable for having 2 waves of influenza A viruses of similar magnitude; the first wave was influenza A (H1N1)pdm09 and the second was H3N2. The overall estimated influenza vaccine effectiveness by virus type and subtype for the 2018-2019 season reported at the June 2019 Advisory Committee on Immunization Practices meeting was 44% against influenza A (H1N1) and 9% against influenza A (H3N2).

The pediatric burden of influenza is significant. Indeed, 185 pediatric deaths were attributed to influenza in the 2017-2018 season, significantly exceeding the average of 60 to 100 pediatric deaths in prior flu seasons. In the 2018-2019 season, 136 pediatric deaths had been reported as of October 23, 2019. These figures are likely understated, as not all cases are reported and not all cases are test confirmed. Each year, the majority of pediatric influenza deaths occur in unvaccinated children.

Patients should be reminded that the burden from influenza is not like that of the common cold; secondary infections such as otitis media and pneumonia increase the risk of poor outcomes from influenza and result in the need for additional treatment beyond that for the influenza itself. In addition to missing work and school, patients with influenza also miss important life activities, such as examinations, sporting events, or recitals, for example. In addition, one must consider the impact of a case of influenza on all of the contacts who become infected due to the short incubation period of 1 to 4 days that the influenza virus has. The high rates of hospitalizations, mortality, and lost productivity are all important consequences that patients must be informed of when physicians are educating them on the importance of getting their influenza vaccines.