Which COVID-19 vaccine is the best?

This post has been updated. It was originally published on January 7, 2021.

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More than a year into the global pandemic, COVID vaccines have become the crucial stepping stone to recovering our normal lives. But even as multiple options have rolled out across the country, some folks are still confused about which COVID vaccine is best or even what they each do. So which should you get?

The answer is straightforward: All three vaccines that are currently available have been shown to be safe and effective. In other words, it does not matter which approved vaccine a person gets, and any option is far better than no shot at all.

Currently, there are two vaccines that require a two shots that have been granted emergency use authorizations from the FDA. Both vaccines, created by Pfizer/BioNTech and Moderna, are mRNA-based. In clinical trials, both have been shown to be around 95 percent effective at preventing laboratory-confirmed COVID-19 illness. The Johnson & Johnson single-shot vaccine has also been granted emergency use authorization and, despite a brief pause, is available across the country. The shot now carries a warning about a very small risk of developing a particular kind of blood clot, but reviews of the data by the CDC and FDA showed that the vaccine was safe.

While Pfizer’s and Moderna’s could more or less be considered sister, or twin vaccines—nearly identical in their function and efficacy—Johnson and Johnson’s is different, with its own set of benefits that set it apart, which begs the question, which should you get? But for now, that question is essentially moot.

“The most common answer you’re going to hear is that we’re not going to have a choice for many, many months, and you’re going to take whatever’s available,” says Susan Kaech, professor and director of the NOMIS Center for Immunobiology and Microbial Pathogenesis. Though it is possible, to some degree, to choose which vaccine you get, there are many situations where you simply can’t. Making a reservation at a local pharmacy will often mean you know in advance which shot you’ll get, but generally large vaccination centers will be giving out whatever is available. And since all of the options provide solid protection against COVID—especially protection against severe disease—it doesn’t much matter which one you get. The main differences are in how the shots work.

[Read more: If you’re fully vaccinated, you (mostly) don’t need to wear a mask outdoors]

Moderna’s and Pfizer’s vaccines both rely on mRNA (messenger RNA) to provide our cells with a blueprint to make copies of an important coronavirus protein. Our immune system recognizes the protein as foreign, learns how to destroy it, and remembers it in case it sees the real coronavirus in the future. The ingredients in the two vaccines differ slightly, as well as the microscopic packaging in which the mRNA sequences come. Because of this, the Pfizer vaccine must be stored at a very low temperature, which limits who can get that vaccine.

The Johnson & Johnson vaccine differs by using a weakened version of a common virus that causes the common cold to get the instructions for coronavirus proteins into humans. This vaccine relies on double-stranded DNA instead of mRNA, and doesn’t require the same level of intense cooling systems as Moderna’s and Pfizer’s. Instead, it can be stuck in a fridge for months at 36 to 46 degrees Fahrenheit. This vaccine had an overall efficacy of 72 percent in the US, and, just as importantly, an up to 85 percent efficacy for preventing severe cases overall. Further, no deaths or hospitalizations were reported with the Johnson & Johnson vaccine trials.

“We have three highly efficacious vaccines that also have a very good safety profile,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, noted at a White House press conference in January.

Several other vaccine candidates are being tested in clinical trials currently. Another from AstraZeneca also uses a weakened adenovirus. A third, from Novavax, injects a lab-made version of a coronavirus protein along with an adjuvant to stimulate the immune system. Phase 3 clinical trial results for the AstraZeneca vaccine showed it to be up to 90 percent effective in preventing disease, slightly less effective than the two mRNA vaccines.

“If you did have a choice, I think I would probably still go with the ones that are showing 95 percent efficacy, but I would certainly be happy to have the other adenoviral-based vaccine if that was what was available to me,” Kaech says. Importantly, Kaech says, “I wouldn’t skip getting a vaccine because the Moderna or the Pfizer vaccines weren’t available.”

Getting vaccinated presents two benefits, Kaech says. Any of the authorized vaccines will protect against severe cases of coronavirus disease. Most vaccines also prevent the illness from being transmitted, and data from early April show that at least the Pfizer and Moderna vaccines were 90 percent effective at preventing infection of SARS-CoV-2. Though they don’t prevent transmission entirely, they do make transmission highly unlikely. Signs point to the Johnson & Johnson vaccine lowering transmission as well. A more mild case of the disease may lower the risk for long-term symptoms or COVID long-haulers, she adds, so even if you get sick after receiving a vaccine, you’ll be better off than if you hadn’t gotten vaccinated.

Barring specific allergies, people in the US don’t generally get to choose the specific vaccine they receive for a given disease. When you take your child to the pediatrician to get a vaccine for diphtheria, tetanus, and whooping cough, for example, you may not know that there are six different pediatric vaccines licensed for that purpose. Individual doctor’s offices (or groups of them) pick which vaccine to order ahead of time. Some places allow you to choose which flu shot you get, especially if you’re allergic to eggs, but many only offer one type.

We’re not used to having a choice of vaccine, which is why multiple options of a coronavirus vaccine may be confusing to some, Kaech says. Still, she notes, it’s a good thing that there are more vaccine candidates being developed and tested. A greater diversity of vaccines will reduce the pressure on manufacturers and vaccine distributors, with the result of increased availability.

“If at the end of a year from now, we have 10 vaccines that are protective, I think it would be just as important as having two highly protective vaccines today,” says Kaech, “because it’ll make the global distribution a lot easier.”

Sara Chodosh

Sara Chodoshis an associate editor at PopSci where she writes about everything from vaccine hesitancy to extreme animal sex. She got her master’s degree in science journalism at NYU’s Science Health and Environmental Reporting Program, and is getting a second master’s in data visualization from the University of Girona. Contact the author here.