# Influenza vaccination patterns among at-risk patients during the Covid-19 pandemic—a retrospective cross-sectional study based on claims data

## TL;DR

This study examines how the Covid-19 pandemic affected influenza vaccination rates among at-risk patients, finding that prior vaccination history strongly predicts future uptake.

## Contribution

The study identifies the impact of the pandemic on first-time influenza vaccination rates and highlights the importance of prior vaccination history as a strong predictor.

## Key findings

- Influenza vaccination uptake increased during the pandemic, with 14.3% of unvaccinated patients getting vaccinated for the first time in 2020/2021.
- A history of vaccinations in all previous seasons was the strongest predictor of vaccination (OR 56.20).

## Abstract

The Covid-19 pandemic may have encouraged at-risk patients to get vaccinated against influenza for the first time. As previous vaccinations are known predictors for further vaccinations, knowledge about individual vaccination patterns, especially in first time vaccinated patients, is of great interest. The aim of this study was to determine influenza vaccination uptake rate (VUR), individual vaccination patterns and factors associated with vaccination uptake among at-risk patients.

The study design was retrospective cross-sectional. Based on claims data, VUR was determined for four influenza seasons (2018/2019—2021/2022). In a cohort subgroup, with data available for all seasons, VUR, vaccination patterns and factors associated with uptake were determined. At-risk patients were people aged ≥ 65 and adult patients with chronic diseases.

We included n = 238,461 patients in the cross-sectional analysis. Overall VUR ranged between 21.8% (2018/2019) and 29.1% (2020/2021). Cohort subgroup consisted of n = 138,526 patients. Within the cohort, 56% were never vaccinated and 11% were vaccinated in all seasons. 14.3% of previously unvaccinated patients were vaccinated for the first time in the first pandemic season (2020/2021 season). The strongest predictor for vaccination was history of vaccinations in all previous seasons (OR 56.20, 95%CI 53.62–58.90, p < 0.001).

Influenza VUR increased during the Covid-19 pandemic, but only a minority of previously eligible but unvaccinated at-risk patients were vaccinated for the first time in the first pandemic season. Previous vaccinations are predictors for subsequent vaccinations and health care professionals should actively address at-risk patients’ vaccination history in order to recommend vaccination in future seasons.

The online version contains supplementary material available at 10.1007/s15010-024-02175-3.