(335) COVID-19 and influenza vaccine co-administration among older U.S. adults

Background: Co-administering COVID-19 and influenza vaccines during a single healthcare encounter is recommended by public health authorities and is intended to improve uptake. However, the extent of vaccine co-administration is largely unknown, especially among older adults.

Objectives: To (1) describe the temporal and geographic distribution of COVID-19 and influenza vaccine co-administration and (2) identify the sociodemographic and clinical factors associated with co-administration.

Methods: We conducted a repeated cross-sectional study using the COVVAXAGE database of CVS Health and Walgreens customers linked to Medicare claims, which represents approximately 75% of the US Medicare population. We identified community-dwelling Medicare beneficiaries ≥ 66 years who received an mRNA COVID-19 booster vaccine between September 1, 2021 and November 30, 2021 (Period 1), and September 1, 2022 and November 30, 2022 (Period 2). The date of beneficiaries’ COVID-19 vaccine represented the study index date. We measured beneficiaries’ sociodemographic (e.g., age, race, and ethnicity), clinical (e.g., comorbidities), and geographic (e.g., rural/urban) characteristics as of and in the 12 months prior to the index date. Within each study period, we measured all influenza vaccinations that were administered. The primary outcome was an influenza vaccine administered on the same day as the index date (vaccine co-administration) compared to a different day or not at all. We estimated adjusted odds ratios (ORs) and 99% confidence intervals (CIs) using logistic regression to describe the association between beneficiaries’ characteristics and vaccine co-administration.

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 periods, though rates were lower in non-White and rural individuals. Vaccine co-administration 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 be co-administered, 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 the co-administration of both vaccines was generally low. Future work should explore which factors explain variation in the decision to co-vaccinate, as well as the safety and effectiveness of co-administration in key clinical subgroups (e.g., persons with cancer and frailty).