A single shot of the Johnson and Johnson COVID-19 vaccine can prevent 85 percent of severe cases of the disease, the company announced today. Overall, it is 66 percent effective against both moderate and severe cases of disease.

“We’re 85 perfect effective at preventing severe disease, which we define as disease that makes you feel particularly sick at home, or may go to the hospital, or worse,” Mathai Mammen, global head of research and development at Johnson and Johnson, told CNN. The company plans to file for emergency authorization next week.

The efficacy is lower than that of the two COVID-19 vaccines already authorized for use in the United States, which prevent about 95 percent of symptomatic cases of COVID-19. Those vaccines each require two doses.

Johnson and Johnson ran its trial in the United States, Latin America, and South Africa. In the United States, the vaccine was 72 percent effective against moderate and severe COVID-19. But in South Africa, where a variant form of the coronavirus is widely circulating, the vaccine was 57 percent effective. Experts have been concerned that the variant, called B.1.351, is different enough from the original virus that vaccines created against the original might not work as well against it. This week, the pharmaceutical company Novavax also announced that its vaccine was less effective against B.1.351 than against other forms of the virus. The first cases of the variant in the US were identified this week.

Still, the data from the Johnson and Johnson trial meets early benchmarks that the Food and Drug Administration set for a COVID-19 vaccine — the agency said last June that it would sign off on vaccines as long as they were at least 50 percent effective.

The Johnson and Johnson vaccine is made by inserting the gene from a snippet of the coronavirus into a harmless, weakened form of an adenovirus, which usually causes symptoms like pink eye or diarrhea. Then, the body produces copies of that virus snippet, and develops antibodies against it. It’s a different strategy than used by Pfizer / BioNTech and Moderna, which insert the genetic snippet into an oily bubble instead.

Even though the vaccine does not appear to work as well as the Pfizer / BioNTech and Moderna vaccines, experts say it could still be useful in the fight against COVID-19, particularly while supplies of the more effective vaccines are still limited. The Johnson and Johnson vaccine offers less of a logistical challenge than the other two, which have to be stored at ultra-cold temperatures and require two shots. This vaccine only takes one shot and can be stored in regular refrigerators.

Paul Offit, a vaccine expert at the University of Pennsylvania, told CNN that he would take a Johnson and Johnson vaccine if it was available before he could get access to either the Pfizer / BioNTech or Moderna shot.

The company is also testing a two-shot regime of it’s vaccine, which might bump up its efficacy.

Johnson and Johnson received funding to develop its vaccine from the US as part of Operation Warp Speed and has an agreement to deliver 100 million doses. The company could ship about 2 million doses as soon as it secures authorization from the FDA.

Over 26 million doses of COVID-19 vaccines have been administered in the US so far.