Does the Johnson & Johnson Vaccine Stand Up to Scrutiny?

How does the Johnson & Johnson vaccine compare with Pfizer and Moderna? A close look at how public health experts discuss the data.

[Update on 4/21/2021: After the CDC and FDA recommended a pause on use of the Johnson & Johnson COVID-19 vaccine on April 13, and after the FDA said on April 21 that unsanitary and unsuitable conditions were found in the Baltimore factory that ruined millions of doses, the situation has obviously changed. The question of the relative merits of this vaccine has become moot for the time being, as it is not currently being offered in the United States.]

When I checked in for my vaccine appointment this week (yay!), I was told I was getting Johnson & Johnson. I had heard, as you probably have as well, that Pfizer’s vaccine has a 95% efficacy in preventing COVID, Moderna has 94%, and Johnson & Johnson has 66%. And I wondered whether this meant I wasn’t getting the best. This post reviews how public health experts are talking about the data on this question.

All three vaccines are excellent. First, all three vaccines–plus Novavax and Astra-Zeneca, which aren’t yet approved in the U.S.–are extremely effective at preventing severe COVID. A tweet from Dr. Ashish Jha, Dean of Brown University’s School of Public Health, pointed out on Twitter that in trials, nobody who’s been vaccinated has died or needed hospitalization due to COVID-19. 

source: Twitter

To be clear, these zeroes aren’t a guarantee that you won’t get severe COVID. The trials included tens of thousands of people, and as the vaccines roll out to millions of people, it’s all but inevitable that we’ll see outliers. In Israel, after over 700,000 people were vaccinated with Pfizer or Moderna, 16 people (or 0.002%) eventually were hospitalized with COVID, according to Vox. Getting severely ill with COVID after vaccination is still possible, just extremely unlikely.

Efficacy numbers aren’t a fair comparison. Back to the comparison. Experts warn that we shouldn’t directly compare the top-line efficacy numbers of the three vaccines, as the trials weren’t conducted head-to-head. This means that there were differences between the trials in the kinds of people who were included and in what numbers, in the protocols, and even in definitions of what constitutes a case or severe case of COVID. 

source: NYT

Most importantly, according to Jha, whereas Pfizer and Moderna were mostly trialed in the United States, Johnson & Johnson was tested in multiple countries including Brazil and South Africa, in the presence of widespread variants and during a more severe phase of the pandemic. Although only real-world use will tell how the vaccines are working in our current conditions, as the above chart from the New York Times shows, all of the vaccines trialed in the presence of B.1.351 have come back with lower efficacy numbers. As Jha and others have observed, it’s a very real possibility that Johnson & Johnson’s lower number is because of these differences in the trial conditions.

So the other way of looking at this is that Johnson & Johnson is the only vaccine currently approved in the U.S. that has trial data showing its efficacy against the more contagious B1351 (South African) variant. And there’s some evidence that Pfizer and Moderna may be weaker against this variant.

Johnson & Johnson’s efficacy continues to grow. Johnson & Johnson’s efficacy also starts early and (ahem) grows over time. In Johnson & Johnson’s application for FDA emergency use authorization, the placebo and vaccinated groups start to have different outcomes as early as one week after the shot, and the efficacy against severe COVID continues to increase for about two months, until it reaches 95% to 100%. Preventing severe COVID and death is the main goal of these vaccines, and by 56 days after your jab, Johnson & Johnson does that spectacularly well.

source: FDA
source: FDA

For most of us, our best shot is the first shot that’s offered. Yes, Pfizer and Moderna have stronger proven efficacy against mild forms of the disease, and the performance of all of these vaccines relative to long COVID remains to be seen. Because of this, Dr. William Schaffner, a professor of health policy at Vanderbilt University, conceded to the New York Times that if he had a choice, he’d pick Pfizer or Moderna. But, he said, that if the choice was between Johnson & Johnson today or another vaccine three weeks from now, he and other experts he knows would take the one that’s available now.

Especially as case counts begin to rise again in the U.S., the vaccine in your arm today is probably worth more than two that may or may not be in your calendar in the future.

The last thing that health experts are talking about is that regardless of which vaccine we each start with, we may all be offered booster shots later. Moderna is testing a booster targeting the South African variant and Pfizer is preparing to do so as well. Johnson & Johnson has a trial underway to test the efficacy of two versus one doses; depending on the results, those of us who started with this vaccine may have a second shot in our future.

Getting an updated COVID shot may become an annual phenomena, like a seasonal flu vaccine, and something called “heterologous prime-boost vaccination”–in which you get a first dose from one manufacturer and a second dose of another kind–is currently being tested. So my Johnson & Johnson shot was my first COVID vaccine, but probably not my last. 

After all this is said, you might still have reasons to pursue or avoid one vaccine in particular. Whether because of logistics or a discomfort with needles, the single-dose Johnson & Johnson may work better for you. If you have an allergy to a specific vaccine ingredient or have other medical needs, your doctor may advise one or another. We’re lucky to have three great vaccines–and all this reading has left me satisfied (and extremely grateful) that I was able to get my shot.

So yes, there are real differences between the vaccines, but for most of us, the vaccine we’re offered first really is the best. 

Recommended Reading and Listening

Finally, a Covid Conversation You Can Feel Good Abou‪t  (podcast) by Ezra Klein, The New York Times (Mar 12, 2021)

Is Choice Always Worth the Anxiety? By Zeynep Tufekci (Mar 8, 2021)

The Differences Between the Vaccines Matter by Hilda Bastian, The Atlantic (Mar 7, 2021)

We’re Not Looking at the Most Important Vaccine Statistic by Kelsey Piper, Vox (Feb 11, 2021)

What do Vaccine Efficacy Numbers Actually Mean? by By Carl Zimmer and Keith Collins, The New York Times (March 3, 2021)

Littldata’s goal is to help parents figure out their family logistics by sharing tools such as maps, calendars, lists, and spreadsheets–as well as research-backed blog posts and data graphics. If you have feedback or ideas for future content, please contact me (Lian) at!

Join Littldata’s mailing list here.

2 thoughts on “Does the Johnson & Johnson Vaccine Stand Up to Scrutiny?”

  1. Thank you for this information and analysis.. My husband and I will take whatever vaccine is available. And I am confident any vaccine will keep us safe from the worst consequences of Covid. However, we have 3 small children, including an infant, who will not likely be vaccinated until 2022. I can’t help but wonder if we (the parents) are more likely to bring home mild or asymptomatic Covid to our unvaccinated children with the Johnson and Johnson vaccine.


    1. I also wonder this! New studies on Moderna and Pfizer have shown that the chance of asymptomatic infections are really low, and similar data on Johnson & Johnson should be coming out soon, so we should find out. Given that J&J’s efficacy against severe disease seems to rise really well over time, my guess (just a guess!) is that it also gets more effective over time against mild/asymptomatic. But only time will tell if it gets as good as Pfizer and Moderna. (If it doesn’t, I hope we’ll be offered a booster.)

      I also think that case rates going down overall, and eventual herd immunity (or close to it), will also protect our kids.

      If I were in the vaccination center and offered a choice, yeah, I’d still take Pfizer. But not all sites let you know what you’re getting before you get it, and I haven’t heard of anyone being offered a choice on the spot.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: