The US Food and Drug Administration (FDA) has granted an emergency-use authorization for a coronavirus vaccine that requires a single inoculation.

The vaccine, made by Johnson & Johnson in New Brunswick, New Jersey, should simplify the logistics of vaccinating people against COVID-19, not only because of its single-dose regimen, but also because it can be stored for up to three months in a refrigerator. Most coronavirus vaccines are given in two doses, and some must be stored at very low temperatures.

Johnson & Johnson’s is the third vaccine against SARS-CoV-2 to be authorized by the FDA. The agency approved it on 27 February, one day after a panel of external advisers voted unanimously that the benefits of the vaccine outweighed any risks.

“It clearly gets way over the bar,” said Eric Rubin, an immunologist at the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, and one of the panel advisers. “And it’s nice to have a single-dose vaccine.”

Johnson & Johnson will provide the vaccine on a non-profit basis for emergency pandemic use, and aims to produce 100 million doses in the first half of 2021.

One-shot wonder

The vaccine works by inserting the gene for a coronavirus protein into a virus called an adenovirus, which has been disabled so that it cannot replicate in human cells. When the adenovirus enters cells, the coronavirus gene is expressed, allowing the immune system to mount a defence against it. The approach is similar to the vaccine devised by the University of Oxford, UK, and AstraZeneca in Cambridge, UK, but uses a different adenovirus.

Johnson & Johnson announced in January that a single dose was 85% effective at protecting against severe COVID-19 in a trial of more than 40,000 people in 8 countries. No one who received the vaccine required medical intervention or died, compared with up to 16 people who received the placebo. The shot was 66% effective at preventing moderate to severe COVID-19.

Superficially, 66% seems lower than the roughly 95% efficacy reported for the two other FDA-authorized mRNA coronavirus vaccines — one made by Pfizer in New York City and BioNTech in Mainz, Germany, and the other by Moderna in Cambridge, Massachusetts. But it is impossible to compare these figures directly. The trials used different definitions of “moderate” disease, for example, and the studies were conducted at different times and in different locations.

“It’s important that people do not think that one vaccine is better than others,” said Cody Meissner, a paediatric infectious-disease specialist from the Tufts University School of Medicine in Boston, at the FDA advisory-committee meeting. “All of them seem to be equally effective in preventing severe disease with intensive-care needs, and death.”

Faster protection

A single-dose vaccine would be simpler to roll out than are those that require booster shots, particularly for hard-to-reach communities, such as people who are homeless, or those living in remote areas. On 24 February, CanSino Biologics in Tianjin, China, announced that its own single-dose vaccine — another adenovirus-based vaccine — is 90% effective at preventing severe disease.

Several FDA advisers expressed concern about the possible future impact of an ongoing trial to test two doses of the Johnson & Johnson vaccine. If that trial, which will report results later this year, finds improved protection from two shots, it is unclear whether people who received one dose under the current single-shot authorization would then be eligible to get another. If they were not, people who received a single shot might feel they are getting a vaccine that doesn’t work as well, said Stanley Perlman, an immunologist at the University of Iowa in Iowa City. Data from a smaller study found that people who received two doses of the vaccine mounted a stronger antibody defence against the coronavirus than after the first dose, suggesting that they could be better protected¹.

But, for the time being, all the FDA advisers agreed that the data were sufficient to authorize the single-dose regimen. Johnson & Johnson’s data also suggest that the vaccine will be effective against the coronavirus variant 501Y.V2 (also called B.1.351), which was responsible for nearly all of the infections in the company’s South African trial. That variant seems to be less susceptible to antibodies raised by infection with earlier variants, and has been found around the world, including in the United States.

“We are in such a fluid situation that what happens in 2, 4, 6 months down the road is going to be very difficult for anybody to say for sure,” said Archana Chatterjee, a paediatric infectious-disease specialist at Rosalind Franklin University in North Chicago, Illinois. “This is going to evolve over time.”