The current available influenza vaccine may have prevented substantial cases of influenza-associated outcomes including illness, medical visits, hospitalizations, and deaths, according to a study recently published in Clinical Infectious Diseases.
During the 2017 to 2018 influenza season, circulation of the influenza virus was widespread for an extended period throughout the United States. The Centers for Disease Control and Prevention estimated that the 2017 to 2018 seasons could have the highest mortality and morbidity since the 2009 pandemic. The primary strategy for influenza illness prevention is vaccination. Midseason estimates of vaccine effectiveness showed 36% against all influenza A and B virus infections and 25% against A (H3N2) virus infections. This study reported the end-of season influenza vaccine effectiveness and estimated the number of vaccine-prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the 2017 to 2018 influenza season.
Vaccine effectiveness and 95% confidence intervals were estimated against medically attended reverse-transcriptase polymerase chain reaction-confirmed influenza virus infection. Further, influenza type/subtype-specific burden was estimated using multipliers applied to population-based rates of influenza-associated hospitalizations. To estimate numbers of influenza-associated outcomes prevented by vaccination, a compartmental model was used.
Results suggested that currently available influenza vaccines reduced the overall risk for any influenza-associated medically attended illness by 38% (95% CI, 31%-43%) and A (H3N2) associated illness by 22% (95% CI, 12%-31%). It was estimated that influenza vaccination prevented 7.1 million illnesses, 3.7 million medical visits, 109,000 hospitalizations, and 8000 deaths related to influenza, when data were modeled with burden and vaccine coverage. Vaccination benefits were the greatest in young children, aged 6 months to 4 years, with 41% of all expected hospitalizations prevented by vaccination.
Overall, the study authors concluded that, “At this time, vaccination remains an important component of influenza prevention; and our results indicate that current vaccines prevent a substantial burden of illness during the 2017-2018 influenza season.”
Rolfes MA, Flannery B, Chung J, et al. Effects of influenza vaccination in the United States during the 2017-2018 influenza season [published online February 2, 2019]. Clin Infect Dis. doi: 10.1093/cid/ciz075/5305915