The one-dose COVID-19 vaccine made by Johnson & Johnson protects against severe disease and has no serious safety concerns, according to a new analysis published today by the US Food and Drug Administration. The report takes the vaccine one step closer to authorization by the agency, meaning the United States could have a third shot available in a matter of days.

The FDA has spent the last three weeks reviewing data submitted by Johnson & Johnson. The company ran its clinical trial in the United States, South Africa, and Latin America. The vaccine was over 80 percent effective at preventing severe cases of COVID-19 in both South Africa and the United States. No one who was 28 days out from their dose of the vaccine was hospitalized with or died from COVID-19.

In the United States, the FDA found that the vaccine was 72 percent effective at preventing both severe and milder cases of the disease 28 days after the shot. That dropped to 64 percent in South Africa, where a variant form of the coronavirus is circulating. COVID-19 vaccines don’t work as well against that variant.

Even though that drop is worrying, the FDA’s analysis of the South Africa data is actually more encouraging than the initial results released by Johnson & Johnson at the end of January. At that point, the vaccine appeared to be only 58 percent effective in the South Africa trial.

New data released by Johnson & Johnson hinted that the vaccine could also protect people from asymptomatic infections (cases where people have the virus but never develop any symptoms). The company tested nearly 1,000 people in the clinical trial 71 days after they received a shot to check if they had antibodies against the coronavirus. If they had antibodies, that was a sign that they’d been infected with the virus (even if they never felt sick). Only two people who received the vaccine had antibodies, compared to 16 people who received a placebo shot.

It’s a promising sign, even though the data is extremely limited. “Definitive conclusions cannot be drawn at this time,” the FDA wrote in its briefing document.

It’s difficult to compare the Johnson & Johnson vaccine to those made by Pfizer / BioNTech and Moderna. Although those two vaccines appeared to be more effective against all cases of COVID-19 where people reported symptoms (around 95 percent), they were tested before coronavirus variants were circulating widely. And even if it’s slightly less effective against mild and moderate disease, the Johnson & Johnson shot only takes one dose and can be stored in refrigerators. The logistical benefits may counteract a slight drop in efficacy.

Johnson & Johnson is asking the FDA to authorize its vaccine for people 18 years of age and older. An independent advisory committee to the agency will meet on February 26th to review the data. The committee will decide if it thinks the FDA should authorize the vaccine, and if all goes well, that authorization could come as early as February 27th.

You can read the FDA’s full report here.