Who should get the Johnson & Johnson vaccine over the mRNA vaccines?

Two COVID-19 vaccines are available in the U.S., and a third, developed by Johnson & Johnson recently submitted an application for emergency use authorization, meaning it could be available in early March. 

With so many options, many people are wondering whether it matters which shot they get.

Related: Quick guide: COVID-19 vaccines and how they work

The short answer is that you should get whichever shot you are offered, experts told Live Science. But there are several reasons why certain shots might work better for different populations. 

The Johnson & Johnson vaccine had 66% efficacy at reducing severe and moderate cases of COVID-19, which include either two mild symptoms or one more serious symptom, such as low blood oxygen levels or increased respiratory rate, Live Science previously reported. In other words, people vaccinated with the J&J shot were three times less likely to get a mild or moderate case of COVID-19 compared with participants who received a placebo. Meanwhile, the Pfizer/BioNTech vaccine had 95% efficacy, and the Moderna vaccine had 94% efficacy at preventing symptomatic COVID-19, meaning any positive test with even one symptom, however mild. All three vaccines are thought to be 100% effective at preventing hospitalization and death related to COVID-19.

But while the Moderna and Pfizer two-shot regimens look, on paper, to be more efficacious, the Johnson & Johnson vaccine has an edge because it doesn't require a follow-up shot and it can be stored at ordinary refrigerator temperatures for months, said Dr. Peter Gulick, a professor of medicine and an infectious disease expert at Michigan State University College of Osteopathic Medicine. That could help with getting more people vaccinated especially those who may not come back for a second shot,  as well as in locales where access is a problem, he said.

The Johnson & Johnson shot's less stringent storage requirements could be an advantage in rural areas, Gulick said. "They can be put in a refrigerator and stored there, whereas Moderna, and definitely Pfizer, need much colder temperatures to keep their vaccine viable," Gulick told Live Science. "The fact you can easily store [the Johnson & Johnson vaccine] in a doctor's office, pharmacy, etc., could make it more accessible." 

This single-shot vaccine also could be better for people who might have difficulty traveling to hospitals or mass vaccination sites (especially those who are home- or bed-bound).

"People get one shot, but there's no guarantee they can come back for the second shot," Gulick told Live Science.

With the rise of new coronavirus variants, some protection is better than no protection. Because a one-shot vaccine such as Johnson & Johnson's only requires one shot, the same number of doses can go twice as far as with the other vaccines, which might be better for controlling the spread of the virus. However, initial supply of the J&J vaccine will be limited; the company initially promised 12 million doses in March, but it may fall behind on production, according to The New York Times.

Dr. William Lang, former White House physician and the medical director of JobSiteCare, told Live Science that the lower efficacy shouldn't dissuade people from getting the Johnson & Johnson vaccine. Unlike Pfizer and Moderna, Johnson & Johnson tested their vaccine against the South African variant, which has been shown to evade neutralizing antibodies, which the immune system deploys to stop the coronavirus from infecting cells.

Related: COVID-19 vaccines: The new technology that made them possible

"The reported lower effectiveness may be somewhat real, but it may also be a function of testing in a slightly different environment because of the newly circulating variants," Lang said. "If my 88-year-old dad or I were offered J&J, I would not hesitate to get it."

Given the emergence of vaccine-evading variants, like the South African and Brazilian variants, reducing spread as quickly as possible is necessary to lower the chances for further mutations to evolve, Gulick said.

On the flip side, the Moderna and Pfizer/BioNTech vaccines, which send mRNA into muscle cells to tell the body to produce an immune reaction to the coronavirus spike protein, do seem to have higher efficacy, Lang said.

Gulick said high-risk groups — such as the elderly, who mount a less robust immune response, and people who are immunocompromised — should be prioritized for vaccines with higher efficacy. 

"I would probably go with the two-dose Moderna and Pfizer vaccine, at least for my patients with HIV. But if the insurance only covers a certain one, I'd say give it to them because I'd just want the vaccine in their arm," Gulick said. "But I would choose the two-dose shot if I had the preference." 

With the world surpassing 100 million COVID-19 cases, according to the World Health Organization dashboard, most of us won't get a chance to pick and choose: It's important just to get vaccinated.

Originally published on Live Science.

Editor's Note: This story was updated on Monday, Feb. 15 at 5:20 p.m. E.D.T. to clarify that  the Moderna and Pfizer vaccines are available, not approved, in the U.S. They were given emergency use authorization, not full FDA approval.