COVID-19 and Influenza Vaccine Coadministration Among Older U.S. Adults

Abstract

Introduction: Coadministering COVID-19 and influenza vaccines is recommended by public health authorities and intended to improve uptake and convenience; however, the extent of vaccine coadministration is largely unknown. Investigations into COVID-19 and influenza vaccine coadministration are needed to describe compliance with newer recommendations and to identify potential gaps in the implementation of coadministration.

Methods: A descriptive, repeated cross-sectional study between September 1, 2021 to November 30, 2021 (Period 1) and September 1, 2022 to November 30, 2022 (Period 2) was conducted. This study included community-dwelling Medicare beneficiaries ≥ 66 years who received an mRNA COVID-19 booster vaccine in Periods 1 and 2. The outcome was an influenza vaccine administered on the same day as the COVID-19 vaccine. Adjusted ORs and 99% CIs were estimated using logistic regression to describe the association between beneficiaries' characteristics and vaccine coadministration. Statistical analysis was performed in 2023.

Results: Among beneficiaries who received a COVID-19 vaccine, 78.8% in Period 1 (N=6,292,777) and 89.1% in Period 2 (N=4,757,501), received an influenza vaccine at some point during the study period (i.e., before, after, or on the same day as their COVID-19 vaccine), though rates were lower in non-White and rural individuals. Vaccine coadministration increased from 11.1% to 36.5% between periods. Beneficiaries with dementia (aOR_{Period 2}=1.31; 99%CI=1.29-1.32) and in rural counties (aOR_{Period 2}=1.19; 99%CI=1.17-1.20) were more likely to receive coadministered vaccines, while those with cancer (aOR_{Period 2}=0.90; 99%CI=0.89-0.91) were less likely.

Conclusions: Among Medicare beneficiaries vaccinated against COVID-19, influenza vaccination was high, but coadministration of the 2 vaccines was low. Future work should explore which factors explain variation in the decision to receive coadministered vaccines.

Figure 1.

Cohort flow diagram of community-dwelling US Medicare fee-for-service beneficiaries who received a COVID-19 booster vaccine between September 1 and November 30 of 2021 (Period 1) and 2022 (Period 2) A greater number of beneficiaries were initially identified for study inclusion in 2021 (N=12,574,957) compared to 2022 (N=5,310,683) because of a change in how COVID-19 vaccines were billed for beneficiaries with a Medicare Advantage plan. Prior to January 2022, COVID-19 vaccinations for Medicare Advantage beneficiaries were billed to Medicare Part B. Beginning in January 2022, COVID-19 vaccinations for Medicare Advantage beneficiaries are billed to their specific Medicare Advantage plan and no longer through Part B. By using the Part B claims to identify COVID-19 vaccinations, we no longer capture Medicare Advantage beneficiaries in 2022, thus reducing the initial population size.

Figure 2.

County-level prevalence of COVID-19 and influenza vaccine co-administration among US Medicare beneficiaries who received a COVID-19 booster vaccine within the study periods