Background Vaccines remain an important public health tool to prevent morbidity and mortality. For influenza, this requires an annual vaccination strategy due to the need to reformulate the vaccine to target circulating strains. The annual success of such vaccine efforts on the annual mortality rates is important to understand and the focus of this study.
Methods Data on vaccination rates and mortality associated with Influenza was obtained from the CDC Morbidity and Mortality Weekly Reports and STATS of the States. In addition, data searches were performed using the CDC WONDER database, local and county health reports, the World Health Organization, and United States census reports.
Results Annual vaccination efforts have had minimal impact on the number of influenza related deaths for those over the age of 65. Additionally, herd immunity has not been achieved in any year at the state and national levels. A closer examination of the 2017 influenza season found that the most populous states had the highest mortality burden. However, there was no correlation in local population density and an increase in influenza mortality.
Conclusion Deaths associated with Influenza circulating in largely populated states are going to occur where susceptible people are regardless of whether they live in rural counties or densely populated cities. Overall, we propose that to prevent annual deaths related to seasonal influenza, herd immunity must be reached in the most populous states. Targeted vaccination of only the susceptible populations is not enough to protect them from mortality associated with influenza.