ITHACA, N.Y. - If an initial COVID-19 vaccine is about as effective as a flu shot, uptake by the American public may fall far short of the 70% level needed to achieve herd immunity, new Cornell research suggests.
In surveys of nearly 2,000 American adults, barely half said they would be willing to take a hypothetical vaccine with an efficacy, or effectiveness, of 50% - the U.S. Food and Drug Administration's minimum threshold for a COVID-19 vaccine, and comparable to flu vaccines.
Vaccine acceptance increased by 10 percentage points, to 61%, if its effectiveness increased to 90%, making efficacy among the most important factors in Americans' willingness to adopt a COVID-19 vaccine, the research found.
"Our results suggest that 50% efficacy will lead to significant vaccine hesitancy," said Douglas Kriner, professor of government at Cornell. "We might not get enough people to take it at that level, even though it would be a valuable public health intervention."
Kriner and Sarah Kreps, professor of government at Cornell, conducted surveys in July asking respondents to choose between hypothetical COVID-19 vaccines based on four medical factors: efficacy, duration of protection and the chances of major or minor side effects.
They also analyzed how political factors influenced vaccine acceptance, including if it was fully approved by the FDA or made available through an Emergency Use Authorization; if it was developed in the United States, United Kingdom or China; and if it was endorsed by President Donald Trump, former Vice President Joe Biden, the U.S. Centers for Disease Control and Prevention or the World Health Organization.
Survey respondents evaluated pairs of vaccines with varying profiles, expressing a preference for one or neither. They then reported their willingness to take each vaccine individually.
Along with improved efficacy, vaccine acceptance improved with a longer protection duration (five years vs. one year) and a lower incidence of major side effects, but by smaller margins (2% and 4%, respectively).
Politically, average willingness to receive a vaccine was lowest when endorsed by Trump, at 52%, but only slightly better for Biden at 55%. Uptake was stronger when endorsements came from U.S. or global public health institutions, improving to 58% for the WHO and 59% for the CDC.
Geopolitics also mattered: Americans' 60% average willingness to receive a vaccine developed in the U.S. dropped slightly if the vaccine came from the U.K. and significantly if it came from China, an outcome that appeared more plausible when the survey was conducted in July, the authors said.
Even one of the best-case hypothetical vaccines presented - developed in the U.K. and approved by the FDA with 90% efficacy, five years of protection, few side effects and CDC endorsement - barely reached the estimated threshold for herd immunity, with 71% of Americans willing to take it.
Kriner and Kreps said the findings can help public health authorities and political leaders develop appropriate endorsements, incentives and messages to broaden vaccine uptake.
The paper, "Factors Associated with U.S. Adults' Likelihood of Accepting COVID-19 Vaccination," published Oct. 20 in JAMA Network Open.
For additional information, see this Cornell Chronicle story.