Comparing the COVID-19 vaccines: If you have a choice, which one should you get?

Pfizer, Moderna and Johnson & Johnson are all safe and effective, but there are some differences.

(Leah Hogsten | The Salt Lake Tribune) Siraj Ahmed, 67, receives his first free Moderna vaccination on Thursday from Salt Lake County Health Department nurse apprentice Bailey Weems. Over 120 people were scheduled to get their first shots of both the Moderna and Pfizer vaccines at the Utah Islamic Center in West Jordan, Mar. 18, 2021.

Utahns are hunting for those vaccine appointments and some are using online services like VaccineFinder.org, which give them a choice they may not have realized they had. Should they check the boxes for Pfizer, Moderna or Johnson & Johnson?

The Centers for Disease Control and Prevention wants you to get the first dose you can get. They’re right — and I’ll be showing you why.

But in case you do have the ability to choose, either now or when vaccine supply starts to outstrip demand, here’s your primer on the differences between the three available vaccines. We’ll also include data on a fourth, the Oxford/AstraZeneca vaccine, that is awaiting U.S regulatory approval.

Current status

[Read more: Utah Department of Health calls for a ‘pause’ in use of the Johnson & Johnson vaccine]

Pfizer’s vaccine is available for anyone 16 and over, while Moderna and Johnson & Johnson are for anyone 18 and up. Studies are underway in children of all ages, but for now, they’ll have to wait. So for you 16- or 17-year old Utahns out there, this is an easy choice.

AstraZeneca is applying for approval right now, and their vaccine is currently being used around the world. They just wrapped up their Phase 3 study in the United States with relatively good results — except that it seems they were doing some funky things.

U.S. regulators said AstraZeneca was presenting “outdated and potentially misleading” data about the efficacy of their vaccine. Essentially, they used data from the middle of their Phase 3 study, rather than at the end, seemingly because the earlier data made their vaccine look better. They seem to have sorted that out and will probably get approval, because we need more vaccines. But this isn’t the kind of thing that they should screw up.

So far in Utah, we’ve received 797,550 doses of the Pfizer vaccine, 740,000 doses of the Moderna vaccine, and 45,000 doses of the recently-approved Johnson & Johnson vaccine.

[Read more: Complete coverage of the coronavirus]

Pfizer and Johnson & Johnson’s manufacturing is accelerating, while Moderna’s is staying stagnant. Utah will receive 93,600 doses of the Pfizer vaccine this week, compared to 74,880 last week. Johnson & Johnson jumped from 3,200 to 16,100 this week. Meanwhile, Moderna has delivered the same 54,200 doses per week for the last seven weeks.

So for those hunting for an appointment, there will be more Pfizer slots available.

How they work

Pfizer’s and Moderna’s are both mRNA vaccines, which is a relatively new technology. Essentially, they introduce genetic instructions to your body’s cells on how to make the spike protein that gives the coronavirus its unique shape. Once those spike proteins are created, your immune system reacts to them, and learns how to prevent future spike proteins from wreaking havoc.

Pfizer’s vaccine was tested with a second dose about three weeks after the first, and Moderna’s vaccine used a second dose four weeks after the first. That being said, the CDC says it’s OK to have that second dose anytime up to six weeks after the first.

Johnson & Johnson’s and AstraZeneca’s vaccine uses a slightly different and more traditional approach: They’ve modified a common cold virus to include genetic instructions for the spike protein. That virus spreads like normal throughout the body, but with these edited instructions that create the spike protein. Then the body’s immune system responds to that.

Johnson & Johnson requires only one dose, while AstraZeneca’s vaccine requires a second. The World Health Organization recommends AstraZeneca’s second dose 8-12 weeks after the first for increased efficacy.

So one way to make a decision would be how fast do you want to be fully vaccinated? Johnson & Johnson’s is the quickest, only one shot. Followed by Pfizer and then Moderna. With AstraZeneca, when it gets approved, we’re not sure what the CDC will recommend, but it could take the longest.

There has been some concern from the vaccine-skeptical community that the mRNA technology that Pfizer and Moderna use is new, and I think some people get scared about the genetic code part of the equation. But in reality, essentially everything you put into your body has a genetic code — that beef you’re eating used to be a cow, you know. The idea that the mRNA is going to hijack or change your genetic material is pretty silly.

Fun fact: vaccines can have trade names, just like other drugs! Pfizer’s brand name for its vaccine is “Comirnaty,” a really ineffective mashup of COVID, mRNA, and immunity. AstraZeneca’s vaccine is called “Covishield.” Ooooh.

Moderna, after filing trademarks for “Spykevax” and “Mvax” among others, just went with “Moderna COVID‑19 Vaccine.” Johnson & Johnson was similarly boring, calling it the “Janssen COVID-19 Vaccine” after the Belgian company that developed it. They went wild in their trademark filings, asking for Rezymnav, Rezymden, Fampelsen, Aqcovsen, Evcoyan, Abfivden, Jcovden, Ovcinden and Jcovav before realizing that no one would ever call it any of those names anyway.

[Read more: Where we stand on vaccinating kids, pregnant women and people who’ve already been infected]


Vaccine efficacy is usually reported as a single number. Generally, to get that number we compare the people who got sick in the vaccinated group to those who got sick in the placebo group, but that raises all sorts of questions: How did they test who got sick? What kind of people were represented in each group? What kind of COVID-19 disease was floating out there?

When you add that in with plain ol’ statistical uncertainty, these numbers are really just estimates. Due to the data worries mentioned earlier, there’s extra reason to be wary of AstraZeneca’s data, but maybe more reason to be confident in the other companies’ data: Pfizer, Moderna, and Johnson & Johnson never raised these red flags.

It’s for reasons like these that scientists advise against comparing the efficacy numbers directly. “It’s Biostats 101: You cannot compare trial results like that unless they were done in a head-to-head fashion,” Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told Vox.

But it’s useful to have those estimates all in one place, without necessarily needing to compare apples-to-apples. Here’s a breakdown of how the vaccine works in various categories.

(Christopher Cherrington | The Salt Lake Tribune)

Against severe disease:

There’s one thing we know: These vaccines are highly effective at preventing the severity of COVID-19 that sends people to the hospital. Both Pfizer and Moderna reported that 100% of vaccinated people avoided severe disease in their trials, and reports from governments tracking these things seem to agree that the risk of COVID-19 hospitalization after getting vaccinated is very, very close to zero.

Johnson & Johnson found that its one-dose vaccine’s protection against severe disease was about 86%. Against hospitalization, it was reported as 100%. AstraZeneca is reporting 100% efficacy against severe disease in international trials.

So if you are looking for a vaccine that will save you from getting hospitalized or dying, all of them are essentially equally excellent.

Against symptomatic disease:

How about just feeling sick?

We start to see more of a difference here. Pfizer reported its vaccine to be 95% effective against symptomatic disease, while Moderna found nearly the same number, 94.1%. Johnson & Johnson’s one-dose study found that it was 72% effective in the U.S. against symptomatic disease. AstraZeneca’s interim data reported 79% effectiveness in the U.S., but after the U.S. government’s tsk-tsking, the company reported 76% effectiveness. That number, though, still needs verification and approval.

Efficacy for elderly:

How well do these vaccines stop symptomatic disease in the elderly? Some of the vaccines chose to report efficacy in this sub-group, while others didn’t — relying on other scientists to study it later.

Once again, Pfizer reported that its vaccine was 94% effective in elderly populations. A study of Moderna’s vaccine found that it was 86% in those over 65 years old.

The estimate for Johnson & Johnson was much lower: researchers found that the vaccine was 42% effective in those over 60 — among those with underlying conditions. The scientists also expressed that they were very uncertain about this number, because of a relatively small sample size. More study should be done here.

Against asymptomatic infection:

The vaccine tests were not very standardized about checking for people who caught the coronavirus, but didn’t experience symptoms, but some follow-up studies have given us more information.

A large study found that Pfizer’s vaccine was about 90% effective at preventing asymptomatic infection after the second dose. Meanwhile, Moderna reported that there were about three times as many instances of asymptomatic infection in its Phase 3 trial in the placebo category compared to the vaccine category, which indicates an effectiveness of about 66%. The sample size was small in that, though, so it could be a wide range.

Johnson & Johnson found similar results for asymptomatic infection as symptomatic infection; providing protection of about 74%. And a study published in The Lancet found that AstraZeneca’s protection against asymptomatic infection was 59%.

Against variants:

In general, there’s evidence that the vaccines are still really effective against the various coronavirus variants, but perhaps somewhat less effective than they are against the basic version of the bug. The number of variants and different locations of testing make this complicated, and it’s hard to get apples-to-apples comparisons.

I’d recommend this Vox article titled “The vaccine race against the coronavirus variants, explained” for more information, but I think it’s fair to say that scientists have generally been encouraged by study results so far.

Side effects:

Of course, you also want to know about side effects. The general overview is that allergic reactions are super rare, there’s no evidence of serious side effects, and the flu-like symptoms that some get go away pretty quickly. That’s the takeaway.

But you, my friends, are Salt Lake Tribune readers, so I know you can handle more detail. In February, the CDC presented the data from 1.6 million people. Now, this survey data came in before people had time to receive the second dose of the Moderna vaccine. What we have is data from both doses of the Pfizer vaccine and one dose of Moderna’s.

(Christopher Cherrington | The Salt Lake Tribune)

First of all, the rates of anaphylactic allergic reaction are really, really tiny, just 4.7 people per million Pfizer patients reacted to the first dose, and 2.5 people per million for the first Moderna dose. I haven’t seen data for anaphylactic reaction for second doses, but that makes sense: If you have an allergic reaction to the first dose, the CDC recommends you shouldn’t take the second.

No matter the dose, about three-quarters of people felt arm pain.

Rates of flu-like symptoms are relatively small after the first dose, but somewhat more common after the second. A majority of people felt some fatigue after the second Pfizer dose, and about three in 10 felt flu-like symptoms like fever or chills. Moderna’s first dose was slightly more likely to incur these side-effects than Pfizer’s.

Still, these side-effects weren’t long-lasting. In general, they were strongest on the day after vaccination, and then typically subsided within two to four days.

And they could have been caused by things besides the vaccine. In one of my favorite vaccine stats, 38% of people who got the AstraZeneca vaccine in their Phase 3 trial reported a side effect (other than arm pain). But, 28% of people who got the placebo also reported a side effect. People get headaches, joint pain, and cold/flu-like symptoms pretty frequently!

What about more serious side effects? The CDC is also checking for those, and comparing them to the rates of those problems in the normal population. Here’s what they found:


About as many strokes and heart attacks and seizures and everything else happened in the vaccinated group as expected. Scientists are also studying every single death that happens after a vaccination and the CDC says, it has “no evidence that vaccination contributed to patient deaths.”

We have less data on Johnson & Johnson and AstraZeneca, though both were found to be very safe in their Phase 3 trials involving tens of thousands of participants. So far, data from international vaccinations of the AstraZeneca vaccine have shown a very good safety profile. There was a scare about blood clotting, but significant analysis from the WHO showed that clotting generally occurred at normal rates post-vaccination.


Let’s sum this up.

All of the vaccines are very safe and very effective, so the CDC’s recommendation to get the first one you can makes sense.

In general, the mRNA vaccines — Pfizer in particular — seem to be slightly more effective than the others, particularly when it comes to avoiding being sick. All do a great job at heading off death or a trip to the hospital.

With the Johnson & Johnson vaccine, there’s the extra benefit of undergoing only one shot, rather than two.

More important than what vaccine you pick is that you pick one. We need to get as many Utahns vaccinated as possible, increasing our levels of immunity communitywide. Go get yours and soon we can get back to living relatively normal lives.

Andy Larsen is a data columnist. He is also one of The Salt Lake Tribune’s Utah Jazz beat writers. You can reach him at alarsen@sltrib.com.

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