Most Americans continue to see Covid-10 vaccines as effective

by Yonatan Margalit (class of ‘22)

It has been just over one year since the Pfizer-BioNTech vaccine received emergency use authorization (EUA), and shots started going into the arms of Americans.

Two more EUA approvals for Covid-19 vaccines, multiple variants, and the introduction of the booster shot later, we find ourselves in an unsure health situation.

Since Covid-19 became international news, back in late 2019 and early 2020, one of the biggest questions people were asking was: how effective will the vaccines be?

For any one vaccine, efficacy can refer to different values. It could describe how well a vaccine protects its recipients from infection, or from hospitalization, or from death. While doctors and scientists might care most about the latter two, avoiding Covid-19 completely is likely just as important to the average person.

When Pfizer and Moderna came out with their Phase III trial results in late-2020 and early-2021, showing 95% and 94.1% efficacy respectively, there was reason to be hopeful. Biotechnology that had been developing since the late 1980s finally got a chance to shine. The mRNA revolution, as known to some, had truly begun.

However, there was a third vaccine that received EUA. Johnson & Johnson’s (J&J) shot did not use mRNA; it was a viral vector vaccine. A person was only required to have one J&J shot in order to be considered fully vaccinated, while the mRNA vaccines required two. Initially, the J&J shot was roughly 70% effective at stopping infection — an efficacy rate that scientists were hoping the most effective Covid-19 vaccines would have.

And yet, Americans did not share this enthusiasm for the one shot J&J vaccine. Among the nearly 40% of Americans who were not at all vaccinated by early-May, the J&J shot was viewed as significantly more undesirable than Moderna or Pfizer and virtually tied with the response “I’d be fine with any of them” — quite a statement when considering that this 40% included most, if not all, anti-vaxxers.

This reluctance to get the J&J shot is best seen from an experiment conducted in a Tufts University poll from May of 2021. All respondents were asked which vaccine they would be most disappointed to receive. If a respondent said they would be most disappointed to receive either “Pfizer”, “Moderna”, “Johnson & Johnson”, or “Endigron” (a fictional vaccine created to see how many respondents would think it was real), the respondents would be given the experiment. If a respondent chose “Novavax” (a company with a real vaccine but unavailable to Americans) or “I’d be fine with any of them”, they would not receive the experiment.

The experiment asked respondents to imagine a scenario where they were selected to receive the vaccine they said would disappoint them most to receive. However, they could wait a week to get a different vaccine — that different vaccine being randomly chosen between “Pfizer”, “Moderna”, “Johnson & Johnson”, and “Endigron” (not including the vaccine they would be most disappointed to receive). Not many people fell for the fictional Endigron vaccine, so those results were not included in my analysis.

Only for the J&J shot would people most disappointed to receive that shot wait a week for a different one. Of the 40% who said they would be most disappointed if they were to receive the J&J shot, 79% would wait a week for an opportunity to get a more preferred vaccine.

Among those who said they would be most disappointed to receive either the Pfizer or Moderna vaccine, only about 30–35% would wait a week for a different one. For both, the majority opted to immediately get the vaccine they would be most disappointed to receive.

What all these results show is that there is a significant drop in enthusiasm for the J&J vaccine, as compared to the Pfizer and Moderna shots, even when the J&J only required one shot and had an efficacy that most scientists could only dream of when the pandemic first hit. When we greatly exceed expectations, we understandably view relatively moderate successes as inadequate, whereas that may not have been the case had Pfizer and Moderna not been such astounding successes.

A question that may arise from these results is: did people truly know the efficacy rates of the three vaccines?

Each respondent was asked how effective they thought the Pfizer, Moderna, Johnson & Johnson, Novavax, and Endigron vaccines were at stopping infection. The results for the first three vaccines are plotted below. The graph shows a high awareness of the efficacy rates as made public by the three biotechnology companies.

For each of the three vaccines, the perceived efficacy against Covid-19 infection had its highest peak near the efficacy rate values publicized at the time. This points to a generally knowledgeable public when it came to vaccine efficacy rates back in May 2021 — the month that the Tufts University poll was fielded.

Interestingly, Pfizer and Moderna’s highest peaks fell slightly short of their true rates, while Johnson & Johnson’s exceeded it. True rates here refer to the rates as given by the companies following Phase III trials, but should not be considered the inherent, final, exact efficacy rate of the vaccines.

That said, each highest peak was not more than a few percentage points off in either direction from their true rates. Also, it is important to note that the J&J vaccine was reported to have a 72% efficacy rate against infection for US trials. The yellow dotted line in the graph above is at 69% efficacy to account for how news outlets reported both the 72% efficacy rate in US trials and 66% overall efficacy rate — 69% being the average of the two, though this number does not hold as much meaning as this general range of values does.

The small peaks at 50% and 0% could be explained for reasons other than genuine belief in these efficacy rates. For the 50% efficacy rate, a peak likely indicates respondents were too apathetic to answer the question and left the value at its starting point on the sliding scale — halfway. For the 0% efficacy rate, a peak likely indicates respondents who are either anti-vaccine or do not believe that the Covid-19 vaccines specifically work at all — though a venn diagram of these two groups could very well just be a circle.

More recent data shows a similarly cognizant American public. The main difference between the data in early May and November is that the Delta variant was not in the public consciousness in the former. By November, the Delta variant had become dominant, one that the original vaccines did not protect against as well as previous strains. In a Data For Progress poll from November, respondents were again asked to indicate how effective they believed the vaccines were at stopping infection without a booster. That is, two shots of Pfizer or Moderna, or one shot of J&J.

The results show a relative dip in perceived efficacy for Pfizer and Moderna, with their peaks close to 87.5%, down from May when they were in the lower-90s. Interestingly, the J&J vaccine peak remains right near 75%, as it was back in May.

When asked how effective respondents believed the vaccines to be with the booster, efficacy rates shot up. Pfizer and Moderna went back nearly to perceived efficacy values seen in May. J&J surpassed that value by almost 13%, its peak now being around 87.5%.

The median perceived efficacies seem to show that people saw all of the vaccines with the booster in November to be as effective as they were without the booster back in May. The median percent efficacies for Pfizer, Moderna, and Johnson & Johnson back in May (before boosters were even considered) were 86, 84, and 72, respectively. The median percent efficacies for these three in November including the booster were 85, 85, and 75. Each of the shots saw a 6–8 percentage point drop between their November perceived efficacy with a booster and without one.

These results show promise in that morale has stayed relatively high regarding the efficacy boosters. Had values stayed the same between perceived efficacies of the vaccines with and without the boosters in November, it would indicate that Americans did not believe getting a booster would help protect them from infection. Had perceived efficacy values been significantly lower in the November data, with or without the booster, compared to those in May, it could indicate that the American people were losing hope in ending Covid-19 through vaccination campaigns.

As the new Omicron variant sweeps across the US and the world, reports have started to come out about the efficacy of the vaccines. Early findings show that a booster from Pfizer can reinstate 75% vaccine effectiveness against symptomatic infection. Other vaccine manufacturers are still in the process of collecting relevant data.

What is important is that, if the vaccine boosters are found to be highly effective against Omicron, messaging stays strong and the populace continues to see them as effective. If the public loses all faith in the vaccines and fully gives up on getting their third shots and all future boosters, an already grim outlook could get a lot worse.



The Tufts Public Opinion Lab (TPOL) is dedicated to studying contemporary controversies in American public opinion using quantitative data analysis.

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Tufts Public Opinion Lab

The Tufts Public Opinion Lab (TPOL) is dedicated to studying contemporary controversies in American public opinion using quantitative data analysis.