High-dose influenza vaccination had higher relative vaccine effectiveness compared with standard-dose vaccination in Medicare beneficiaries aged ≥65 years, and was more effective across all seasons for adults aged ≥85 years, according to study results published in the Journal of Infectious Diseases.
Previous studies concluded that high-dose influenza vaccines were more effective than standard-dose vaccines, but only for certain seasons. Investigators conducted a retrospective cohort study to assess the effects of high- vs standard-dose vaccines in adults aged ≥65 years across 6 influenza seasons. A total of 13,770,207 high-dose and 6,151,913 standard-dose vaccinated Medicare beneficiaries were eligible for analysis. The outcomes were influenza-related hospital encounters including inpatient stays or emergency department visits.
A slight increase in relative vaccine effectiveness with increasing age for all seasons was observed. Hospital encounters were better prevented by high-dose vaccines than by standard-dose vaccines for 4 seasons, and were at least as effective for the other seasons. For individuals aged ≥85 years, high-dose vaccines were steadily more effective than standard-dose vaccines across all seasons.
“[T]he magnitude of [relative vaccine effectiveness] differed by influenza season,” wrote the authors. “[Relative vaccine effectiveness] could vary by influenza season due to the complex effects of factors such as predominant circulating strain, influenza outcome [incidence rates], or reported antigenic similarity of vaccine strain and circulating strain.”
The researchers noted that they have started multiple projects to address unmeasured confounders associated with this study.
Lu Y, Chillarige Y, Izurieta HS, et al. Effect of age on relative effectiveness of high-dose versus standard-dose influenza vaccines among US Medicare beneficiaries ages 65 years and older [published online July 9, 2019]. J Infect Dis. doi:10.1093/infdisjiz360