# Influenza Vaccination and COVID-19 Mortality in the USA: An Ecological Study

## TL;DR

This study finds that higher influenza vaccination rates in the elderly are linked to lower COVID-19 mortality at the county level in the USA.

## Contribution

The study identifies a negative association between influenza vaccination coverage in the elderly and county-level COVID-19 mortality.

## Key findings

- Influenza vaccination coverage in the elderly is negatively associated with county-level COVID-19 mortality.
- The association remains consistent across different methods for adjusting confounding factors.
- The study suggests the need for individual-level research to explore biological mechanisms behind the observed relationship.

## Abstract

The COVID-19 mortality rate is higher in the elderly and in those with pre-existing chronic medical conditions. The elderly also suffer from increased morbidity and mortality from seasonal influenza infections; thus, an annual influenza vaccination is recommended for them. In this study, we explore a possible county-level association between influenza vaccination coverage in people aged 65 years and older and the number of deaths from COVID-19. To this end, we used COVID-19 data up to 14 December 2020 and US population health data at the county level. We fit quasi-Poisson regression models using influenza vaccination coverage in the elderly population as the independent variable and the COVID-19 mortality rate as the outcome variable. We adjusted for an array of potential confounders using different propensity score regression methods. Results show that, on the county level, influenza vaccination coverage in the elderly population is negatively associated with mortality from COVID-19, using different methodologies for confounding adjustment. These findings point to the need for studying the relationship between influenza vaccination and COVID-19 mortality at the individual level to investigate any underlying biological mechanisms.