Which vaccine should I take?

How to make sense of the trade-offs between different COVID-19 vaccines. And why you should take the first one you can get.

The Johnson & Johnson (J&J) vaccine, authorized for emergency use last weekend, adds a tremendous new tool to our anti-COVID-19 arsenal. Administered in one shot that doesn’t require deep freezing like it’s mRNA-based cousins, it’s far easier to deploy—critical in a moment when deployment has been our achilles heel. 

And yet some are casting aspersions on the J&J vaccine—arguing that they’d rather wait for “the best” vaccine, rather than settle. This is wrongheaded and threatens to defeat our ability to bring an end to this pandemic overall. Here’s why.

A review: Moderna vs. Pfizer vs. J&J.

The Pfizer/BioNTech and Moderna vaccines were the first to market, deployed way back in 2020 after the FDA issued their emergency use authorizations. They are excellent vaccines. In trials, they were 95% and 94.1% effective in preventing any symptomatic COVID-19 infection after the second dose. Their side-effect profile is minimal—usually soreness at the injection site or mild malaise after the second injection, which is a function of your immune system revving up to take on what it perceives as an infection (which is the point of the vaccine!). In extremely rare cases among people with a history of anaphylactic reactions to medication, the vaccines can trigger an anaphylactic reaction. That’s why everyone who is vaccinated must wait 15 minutes under the supervision of a healthcare provider before leaving the premises. Personally, the only side effect I experienced after receiving my second Pfizer vaccine was a touch of grogginess for the first 24 hours after the second dose. 

The J&J vaccine is an equally excellent vaccine. In the US arm of its trial, it was 72% effective against moderate COVID-19 infection, 85% effective against severe infection, and 100% effective against hospitalization or death to COVID-19 28 days after vaccination. It’s side-effect profile is similar to the other two vaccines for the same reasons—though there has been only one documented case of anaphylaxis in anyone who has received the vaccine.

The matter of 23%.

In their trials, two of these vaccines are about 95% effective, and one of them is 72% effective. Let me pose the uncomfortably obvious question up-front—so I can explain why it’s not the right question to be asking: 

“Why would I take a vaccine that’s 23% less effective?” 

Implicit in this question is a head-to-head comparison between vaccines. But it’s nearly impossible to compare trial outcomes this way. Why? First, the Pfizer and Moderna trials both started in late July—tracking patients mainly through November. That was well before cases started to spike around the holidays. By contrast, the J&J vaccine trial began in September, as cases started to trend upward and tracked patients through January. 

That might not sound like it matters, but here’s why it does. In trials, you take healthy volunteers and randomize them to receiving either the vaccine or a placebo. You follow the volunteers through the study period and compare the likelihood of having been infected, having been moderately or severely ill, or having died of COVID-19 across groups. But there are two ways someone in your trial doesn’t get sick: either they aren’t exposed, or they are exposed and the vaccine protects them. When the baseline probability of illness is lower, the proportion of people who don’t get sick because they simply weren’t exposed increases. That can make the vaccine seem more effective simply because people weren’t exposed to the virus in the first place. Pfizer and Moderna trials took place while transmission was lower, which could make them look better as compared to Johnson & Johnson.

And that’s only one reason it's hard to compare the vaccines.

New evidence suggests that more transmissible SARS-CoV-2 variants have been spreading in the US since the fall—when the J&J vaccine was in trials. That means J&J was tested, in part, against variants, while Pfizer and Moderna, tested before variants had emerged and began spreading, were not.

So while it’s tempting to extrapolate from top-line trial data, it’s not really a fair comparison. Though a cursory look at the numbers would suggest that Pfizer or Moderna’s vaccines are “better,” J&J was tested in an environment that looks more similar to the one we face right now, which could be “better.” But this all reminds us that we’re comparing apples to oranges. And right now, we just need fruit!

How vaccines actually work.

Vaccines give our immune system the biological equivalent of a “Be on the Lookout” call, telling it what to look for so that it can mount up its considerable resources to defeat the virus. In doing that, our body has the resources it needs ready to go the minute the virus enters—and can make easy work of defeating the virus before it can spread and multiply. 

But that’s only the physiology. In fact, the most important value of vaccines occurs at the population level—though a collective “herd” immunity. I want to clearly define this, because herd immunity got a bad rap early in the pandemic. 

Herd immunity is the immunity we receive from others because they are immune. If we develop enough immunity together, it stifles the spread of a disease. 

Early in the pandemic, some advocated a “herd immunity” approach to this pandemic. They believed that the best way to deal with it was to quarantine those most vulnerable to serious illness and death—older people and those with pre-existing conditions—while allowing the virus to simply spread among everyone else. This way, they argued, if enough people got sick and developed immunity after recovery, we’d develop herd immunity, bringing the pandemic to an end. 

There were three flaws in that thinking: first, it’s very hard to effectively quarantine the most vulnerable people. We attempted to do that and nursing homes still accounted for upwards of 40% of COVID-19 mortality early in the pandemic. Second, it assumes that there wouldn’t be any serious illnesses among people who didn’t seem particularly vulnerable. Yet COVID-19 had killed over 4500 people aged 25-44 by July. Not to mention that nearly 30% of people who’ve recovered from COVID-19 still report long-term symptoms. And finally, it assumes that the virus can’t evade our disease-acquired immunity—which new variants are proving incorrect every day.

This do-nothing-and-hope-for-the-best approach isn't the herd immunity we’re talking about today—instead, we’re talking about vaccinating as many people as possible as fast as possible to smother the virus. It’s like putting a blanket on a fire. If we can get enough people immune fast enough, the virus has fewer avenues to spread—and the pandemic dies out. 

This collective immunity requires speed and comprehensiveness. Imagine throwing that metaphorical blanket on some small part of a fire slowly, instead of the whole thing all at once. Rather than smothering the fire, the blanket would be consumed by it. That’s the risk awaiting our vaccines if we can’t get enough people vaccinated fast enough—new variants are likely to arise that are resistant to vaccine-mediated immunity, too, rendering them useless. 

So, which vaccine should I take?

Right now, we need to use every vaccination at our disposal. Which is why the right vaccine for you is the first vaccine you can get. Shopping around for the “right vaccine” isn’t just wrongheaded—it’s dangerous. Every day we delay getting vaccines into arms is a day more the virus has time to spread and mutate. 

So get vaccinated as soon as you can. I know that, for many folks, this advice is probably redundant. Of course you’re trying your hardest to get vaccinated. But here’s where the rubber hits the road: as soon as your number is called, get that vaccine—no matter whether it's Pfizer, Moderna, or J&J! And push your public officials to get as many vaccines as they can--particularly to low income communities and communities of color, where vaccines have been harder to come by.

The J&J vaccine is critical to allowing us to vaccinate more quickly and more comprehensively. And choosing not to use it leaves an important tool in our armament off the table—and could defeat our vaccines overall, no matter their trial-based efficacy.