Relationship between Covid-19 vaccination and flu vaccination rates | NEJM

To the editors:

The polarizing nature of vaccination against coronavirus disease 2019 (Covid-19) in the United States threatens public health and has contributed to variable vaccination rates across the state that have ranged from 50 to 80% as of January 2022.1 Given the divided national landscape and anecdotal evidence from our own patients, we hypothesized that low Covid-19 vaccination rates would be associated with reductions in flu vaccination rates.

Using nationally representative data from the Centers for Disease Control and Prevention,2 we calculated changes in flu vaccine uptake at state population level during the pandemic after Covid-19 vaccines became generally available (September 2021 through January 2022) compared to before the pandemic (September 2019 through January 2020) . To account for pandemic factors unrelated to Covid-19 vaccines that may affect changes in flu vaccine uptake (eg.3.4 or employment), we compared September 2020 through January 2021 (the first flu season during the pandemic but before widespread availability of Covid-19 vaccines) with pre-pandemic. We stratified changes in flu vaccine uptake by quartile of cumulative state-level Covid-19 vaccine uptake through January 2022. We used mixed-effects linear regressions (difference-in-differences analyses) to investigating whether changes in flu vaccine uptake during flu seasons before and during the pandemic differed between states with high compared to low Covid-19 vaccine uptake. Details and sensitivity analyzes can be found in the: Additional attachmentavailable with the full text of this letter at NEJM.org.

Trends in flu vaccine uptake aggregated by quartile of Covid-19 vaccine uptake statewide among all adults, all children, and older adults.

Each flu season runs from September of the indicated year through January of the following year (for example, the 2021 flu season ran from September 2021 through January 2022). An explanation of the decline in flu vaccine uptake during the 2017-2018 season, in addition to further interpretation of the results, is available in the Discussion section in the Additional attachment† Covid-19 stands for coronavirus disease 2019.

Flu vaccine uptake remained relatively stable during the first flu season of the pandemic (Figure 1† By contrast, after Covid-19 vaccines became widely available (2021-2022 season), adult influenza vaccine uptake declined in states in the bottom two quartiles of Covid-19 vaccine uptake (quartile 1, from 43.7%) [95% confidence interval {CI}, 41.8 to 45.6] up to 39.2% [95% CI, 37.0 to 41.5]† quartile 2, from 45.5% [95% CI, 42.8 to 48.2] up to 43.5% [95% CI, 40.4 to 46.7]) and increased within states in the top two quartiles (quartile 3, from 46.9% [95% CI, 45.1 to 48.8] up to 47.7% [95% CI, 45.1 to 50.4]† quartile 4, from 49.0% [95% CI, 46.7 to 51.4] up to 52.8% [95% CI, 50.2 to 55.3]) (Table S1 in the Additional attachment† Differences between each quartile in the 2021-2022 season compared to the 2019-2020 season are shown in Table S2. The sensitivity analysis comparing the 2020-2021 season with the 2019-2020 season showed that flu vaccine uptake was stable before the widespread availability of the Covid-19 vaccine, suggesting that other pandemic effects, such as changes in access to care, affected flu vaccine uptake. During the 2020-2021 and 2021-2022 flu seasons, flu vaccine intake in children declined evenly, but remained stable in older adults regardless of Covid-19 vaccine intake.

While conclusions on specific policies and messages promoting Covid-19 vaccination are beyond the scope of this environmental study, our findings suggest that following the widespread availability of Covid-19 vaccines, factors associated with Covid-19 vaccination rates (e.g. . safety concerns and mistrust) of Covid-19 vaccines or the government5) may have been skipped to affect flu vaccination coverage.

Richard K. Leuchter, MD
Nicholas J. Jackson, Ph.D., MPH
John N. Mafi, MD, MPH
Catherine A. Sarkisian, MD, MSHS
David Geffen School of Medicine at UCLA, Los Angeles, CA

Supported by grants from the National Institutes of Health (NIH), National Institute of Heart, Lung and Blood, promoting access to Research in Residency program at UCLA (5R38HL143614-03, to Dr. Leuchter); the NIH, National Center for Advanced Translation Studies UCLA Clinical and Translational Science Institute (UL1TR001881, to Dr. Sarkisian); the NIH, National Institute on Aging (1K76AG064392-01A1, to Dr. Mafi); and the NIH, National Institute on Aging Midcareer Award in Patient Centered Aging Research (2K24AG047899-06, to Dr. Sarkisian). dr. Sarkisian was also supported with resources and use of facilities at the Veterans Affairs Greater Los Angeles Healthcare Center.

Disclosure Forms provided by the authors are available with the full text of this letter at NEJM.org.

This letter was published on NEJM.org on June 15, 2022.

  1. 1. Center for Disease Control and Prevention. COVID-19 vaccinations in the United States, province. 2022https://data.cdc.gov/Vaccinations/COVID-19-Vaccinations-in-the-United-States-County/8xkx-amqh

  2. 2. Center for Disease Control and Prevention. FluVaxView: flu (flu). 2021https://www.cdc.gov/flu/fluvaxview/index.htm

  3. 3. Leuchter RKVillaflores CWANorris KCSörensen AVangala SSarkisian CA† Racial disparities in potentially avoidable hospitalizations during the COVID-19 pandemic. Ben J Previous Med 2021;61:235239

  4. 4. Mafi JNCraff MVangala S, et al. Trends in outpatient care patterns in the US during the COVID-19 pandemic, 2019-2021. JAMA 2022;327:237247

  5. 5. Khairat SWould BAdler-Milstein J† Factors and reasons associated with low COVID-19 vaccine uptake among highly hesitant US communities. Ben J Infect Control 2022;50:262267

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