By Seema Gupta, MD, MSPH

Clinical Assistant Professor, Department of Family and Community Health, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV

SYNOPSIS: Efficacy, protection duration, side effects, and FDA approval factored into decisions about choosing a COVID-19 vaccine.

SOURCE: Kreps S, Prasad S, Brownstein JS, et al. Factors associated with US adults’ likelihood of accepting COVID-19 vaccination. JAMA Netw Open 2020;3:e2025594.

The success of any strategy to ensure maximum vaccine uptake depends on the rate of acceptance and hesitancy. The United States remains the leader in both COVID-19 cases and related deaths on a per capita basis.1 As vaccines have become available, most experts agree widespread public acceptance of a COVID-19 vaccine is imperative for stemming the pandemic.

The wide availability of COVID-19 vaccines presents our best pathway to herd immunity and recreating some sense of normalcy in the United States. Currently, only 60% of the population has been fully vaccinated.2 This has led to some improvements in case and death rates, but vaccination efforts remain uneven across the country. Certain communities continue to carry an inequitable burden of disease and remain more susceptible to morbidity and mortality. To achieve herd immunity, overcoming vaccination resistance and hesitancy is critical.

Before COVID-19 vaccines were widely available, Kreps et al surveyed 1,971 U.S. adults to gauge what factors might play into decision-making (median age = 43 years; 51% of respondents were women, 73% were white, 14% were Black, and 10% were Latinx). The authors used a choice-based conjoint analysis to estimate the probability of choosing and receiving a vaccine. For each of the five choice tasks, respondents analyzed two hypothetical vaccines and picked an option (vaccine A, B, or neither). Attributes analyzed included minor and major adverse effects, protection duration, efficacy, FDA approval, endorsements, and national origin.

Researchers learned the more efficacious the vaccine, the more likely respondents were to seek the shot. An increase in the duration of vaccine protection from one year to five years and a decrease in the incidence of major adverse effects from one in 10,000 to one in 1 million also were associated with a higher probability of choosing a vaccine.

A vaccine that had received only an FDA emergency use authorization, not full approval, was associated with a lower probability of choosing a vaccine. If a vaccine originated outside the United States, respondents were less likely to seek the solution, especially if the shot was made in China. Vaccines with CDC and World Health Organization (WHO) endorsements carried more weight with respondents than any vaccines endorsed by then-President Trump.


The unprecedented politicization of the public health response to the COVID-19 pandemic has led to less-than-sufficient deployment of public health measures, resulting in more lives lost, more suffering, and an economic fallout. But was it all predictable? Could we have avoided it? Well, yes and no. Studies like those from Kreps et al clearly outlined a range of factors that may be associated with a better understanding of vaccine resistance and hesitancy. But recommendations and advice regarding a vaccine may be more complicated in the context of COVID-19 compared with other diseases, such as the seasonal influenza. Factors associated with higher probability of choosing a vaccine, such as better efficacy, low incidence of major adverse effects, and endorsements by the CDC and WHO, currently exist.3 But the FDA has been slow to approve vaccines, and the ongoing politicization of science, from mask-wearing to vaccine mandates and school openings, has led to an erosion of the public’s confidence in vaccines.4,5

Vaccines were a chance to redeem failures in the U.S. coronavirus response. But it did not happen, and more lives are lost daily as a result. For policymakers and health experts alike, the lesson may be that even perceptions of political influence, much less interference during a pandemic response, significantly undermine the viability of countermeasures deployed, including a vaccine as a strategy to end that pandemic. Perhaps, in the next pandemic (which is sure to happen), we will try to remember that.


  1. Johns Hopkins Coronavirus Resource Center. COVID-19 dashboard. Updated Dec. 13, 2021. 
  2. Centers for Disease Control and Prevention. COVID-19 vaccinations in the United States. Updated Dec. 12, 2021. 
  3. Centers for Disease Control and Prevention. Selected adverse events reported after COVID-19 vaccination. Updated Nov. 30, 2021.
  4. Meo SA, Bukhari IA, Akram J, et al. COVID-19 vaccines: Comparison of biological, pharmacological characteristics and adverse effects of Pfizer/BioNTech and Moderna vaccines. Eur Rev Med Pharmacol Sci 2021;25:1663-1669.
  5. Chernozhukov V, Kasahara H, Schrimpf P. The association of opening K-12 schools with the spread of COVID-19 in the United States: County-level panel data analysis. Proc Natl Acad Sci U S A 2021;118:e2103420118.