Although elderly influenza vaccination coverage increased from ∼15% to ∼65% during 1980–1999 in the US, estimates of influenza-related mortality also increased during this period. We examined these apparently conflicting findings by adjusting mortality estimates for aging within the elderly and the incidence of influenza A (H3N2) virus circulation. Using national mortality statistics for 1968 through 1999, we generated age-specific monthly rates for pneumonia and influenza (P&I) and all-cause mortality for persons ≥65 years of age. We estimated influenza-related mortality as the winter excess in mortality over a Serfling model baseline. After adjusting for age and considering only A (H3N2)-dominated seasons, we found that excess mortality declined sharply among younger elderly (65–74 years) during 1968–1980, but remained level after 1980. Among the most elderly (85+ years), excess mortality rates were essentially unchanged over the entire study period. In conclusion, the increase in elderly influenza vaccination coverage in the US after 1980 was not accompanied by a decline in influenza-related mortality. We hypothesize that disparity in vaccination rates among frail elderly, combined with reduced responsiveness to vaccination with age, may account for these findings.
Simonsen, L., Reichert, T. A., Blackwelder, W. C., & Miller, M. (2004). Benefits of influenza vaccination on influenza-related mortality among elderly in the US: An unexpected finding. International Congress Series, 1263, 163-167. https://doi.org/10.1016/j.ics.2004.02.038, https://doi.org/0.1016/j.ics.2004.02.038