Will People Embrace a COVID Vaccine? It Depends

F. Perry Wilson, MD, MSCE


October 21, 2020

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This transcript has been edited for clarity.

Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I'm Dr F. Perry Wilson from the Yale School of Medicine.

So... are you going to get it? The COVID vaccine, I mean. It has been said many times before, but it bears repeating: The fact that we are even talking about mass vaccination for a disease that was unknown a year ago is mind-blowing. Vaccine development takes decades. But through unprecedented work, here we are.

Of course, the speed with which we got here has led to some uncertainty. Recent surveys suggest that somewhere between 50% and 70% of US adults said they will get a COVID vaccine when it is developed.

That may not be enough to squelch the pandemic. The vaunted "herd immunity" threshold for SARS-CoV-2 suggests that we'll need about 70% of the population to be vaccinated or, you know, become infected naturally. But characteristics of the vaccine may affect uptake. It turns out that this matters a lot, as this study appearing in JAMA Network Open shows us.

Researchers from Cornell University surveyed 2000 adults representative of the US population. They used a powerful technique called conjoint analysis to get their results. The short version: Instead of asking them if they would be more or less likely to accept a vaccine given certain conditions, they were presented with two different theoretical vaccine profiles — like this — and they had to choose which they would take, or neither.


The elements in the profiles (the effectiveness, the side-effect rate, the provenance, the endorsements) were varied randomly. Because of that, they could triangulate how any one factor might move the needle on vaccine acceptance.

The results were fascinating.

The most important factor? Vaccine efficacy. People were about 20% more likely to accept a 90% effective vaccine compared with a 50% effective vaccine. I'll note that the FDA has put 50% efficacy as the minimum acceptable threshold for approval of a vaccine candidate.


Next up: side effects. A vaccine with a 1-in-a-million risk for major side effects was about 10% more likely to be accepted compared with one with 1-in-10,000 risk.


People didn't like vaccines approved under an emergency use authorization (EUA) (spoiler alert: Any COVID vaccine is very likely to be approved in just this manner), reducing their willingness by around 5%.


Vaccines from the United States were most trusted. If the vaccine came from China, the rates of acceptance dropped 15%.


Compared with getting a thumbs-up from President Trump, a vaccine endorsed by the CDC or WHO was significantly more likely to be accepted. But the Biden effect was not as strong. Caveat here: I'm not sure why these are mutually exclusive categories; there's a big difference between a vaccine endorsed by Trump but not by the CDC, vs one endorsed by both.


In any case, using these data, we can construct best- and worst-case scenarios for when a vaccine actually does come out.


Best case? A 90% effective vaccine with extraordinarily rare side effects that was developed in the United States, underwent full approval by the FDA, and is endorsed by the CDC. About 70% of people would accept such a vaccine.

Worst case? A 50% effective vaccine with an adverse event rate of 1 in 10,000 that comes from China, got an EUA from the FDA, and is endorsed by President Trump. According to this model, just 12% of people would accept such a vaccine.

I'm frankly a bit concerned by these numbers. The best-case scenario would be a literal blockbuster vaccine; it would be a real miracle to see numbers like that — and we'd still be at just 70% uptake. The worst-case scenario is not entirely implausible either, by the way. Remember, 50% efficacy is the floor for the FDA to consider an EUA for a vaccine. We may literally be looking at a vaccine like this. And personally, I'd still probably get it, provided that the data were vetted by the Vaccine and Related Biological Products Advisory Committee at the FDA. No end-runs around the independent scientists, please.

The study also looked at individual characteristics of the participants to see what factors, all else being equal, were associated with vaccine acceptance. Concerningly, given the disproportionate burden in the pandemic, Black people were less accepting of vaccines. So were women, people who were more poorly educated, and those who didn't personally know someone with COVID-19.


Overall, this study tells us that we have our work cut out for us. Vaccination is our key out of this nightmare. We need to set expectations now so that uptake remains high, even if that eventual vaccine isn't the blockbuster we're all hoping for.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and director of Yale's Program of Applied Translational Research. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He tweets @methodsmanmd and hosts a repository of his communication work at

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