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Does It Matter Which COVID-19 Vaccine You Get?

By the end of this week, the United States could have not one, but two COVID-19 vaccines authorized for emergency use. After nine months of isolation and lockdowns and more than 300,000 deaths, it is difficult to find superlatives to fit this moment. Any I come up with feel like they still understate how fantastic the news truly is. What’s more, there are even more vaccines waiting in the wings. Within a few months, we will likely have access to vaccines by Pfizer and Moderna … and Johnson & Johnson, and Novavax, and AstraZeneca. We’re going to go from desperately wishing for a vaccine, any vaccine, to having a cornucopia of choices.

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But that doesn’t necessarily mean you’re going to have much ability to choose between them. At least, not anytime soon.

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While people at the tail end of the vaccination priority list will likely be able to browse a veritable vaccine buffet, anyone getting vaccinated in the next few months is probably just going to have to take what’s available. That’s going to be especially true in the immediate short term, as limited supplies begin to circulate but the biggest issue remains whether any vaccine is available — not which one you want.

This is not, however, bad news. That’s because the first two vaccines available are far more effective than anyone expected they would be, and experts say either one would be great to take. It’s also not totally unprecedented. There are multiple versions of many of the vaccines we already take. For instance, there are multiple flu vaccines available every year. What’s different is the public’s awareness of the many potential vaccine options, said Dr. Rebecca Weintraub, a professor of medicine and global health at Harvard Medical School.

Our need for all those options is also a bit different, she and other experts told me. The variety of flu shots helps serve different populations — seniors need one with a higher dosage, for example, and people who are allergic to eggs need one produced without those triggers. But, in the short term, at least, the main reason we want lots of COVID-19 vaccines is because we need the extra manufacturing capacity that provides. “If we’re going to vaccinate more than 300 million people in this country, in the end we’re going to need more than two vaccines,” said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia. “You want to get on top of this as quickly as you can. You want to get back to normal as quickly as you can, so the more manufacturers the better.”

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And right now, the differences between the two vaccines that will be ready soonest are basically negligible, experts told me. Both Pfizer and Moderna have short-term efficacy rates near 95 percent. Both have low rates of severe side effects — though, based on analysis of clinical trial data, Pfizer’s appear to be a little lower than Moderna’s. Pfizer was also tested on a different age range and is authorized for people as young as 16, while Moderna is only seeking authorization for those age 18 and older. But that’s about it. You won’t be able to choose if you get Pfizer or Moderna … but it also really doesn’t matter at this point, experts said. You should feel confident with either.

Eventually, we will get to the point where we know more about how different vaccines better serve this or that niche population. Maybe one turns out to provide better protection for elderly people. Maybe another produces fewer allergic reactions, like the kind that happened this week in Alaska during the Pfizer rollout. It may even turn out that one or another vaccine lasts longer and requires fewer booster shots. But that data isn’t currently available, Weintraub said, because the clinical trials weren’t designed with cross comparison of the vaccines in mind.

“The endpoints are slightly different. The study populations are slightly different. So we’re not on the same field with the same exact rules when we’re comparing these clinical trials, unfortunately,” she told me.

That lack of cross comparison matters, as does the lack of information we currently have about things like how different vaccines interact with one another. “We see now that, for example, AstraZeneca is thinking about combining their vaccine with Sputnik V, the Russian vaccine, to try and gain even greater potency and breadth of coverage,” said Dr. Warner Greene, senior investigator at Gladstone Institutes, an independent, nonprofit biomedical research center in San Francisco. But currently, it wouldn’t be a good idea to get one vaccine and then decide you want to try another, because we don’t know how the two vaccines would interact (even though it’s completely possible some of those interactions could be beneficial).

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Right now, though, you would not want to get one dose of Pfizer and your second dose of Moderna, said Dr. Purvi Parikh, a professor at New York University’s Grossman School of Medicine and a co-investigator on the Pfizer vaccine trials. The two are both mRNA-based vaccines, but they’re different enough that you can’t assume they’re interchangeable without research to prove it. In fact, she told me, people who get vaccines will be getting cards to document both when they are due for their second shot — and which vaccine they should get when they go back for it.

All of this is why Weintraub says it’s critical that funding and volunteering for Phase 3 clinical trials continue, even after we have two vaccines on the market. We need to have more vaccines reach authorization than just Pfizer and Moderna, and we need to know how all the authorized vaccines compare to one another. If we ever want multiple vaccines to really mean multiple options, we have to keep learning about them. Otherwise, no matter how many vaccines we have, we won’t be able to make an informed choice between them.

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Maggie Koerth was a senior reporter for FiveThirtyEight.