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In an analysis released Wednesday, the US Food and Drug Administration said the Johnson & Johnson Covid-19 vaccine has met the requirements for emergency use authorization – another step toward the authorization of a third shot for the United States.

The efficacy of the Johnson & Johnson vaccine against moderate to severe/critical Covid-19 across all geographic areas was 66.9% at least 14 days after the single-dose vaccination and 66.1% at least 28 days after vaccination, according to the analysis, which is meant to brief the FDA’s Vaccines and Related Biological Products Advisory Committee.

The committee is an independent group that determines if the vaccine works and if it’s safe. After the group meets Friday, it will make its authorization recommendation to the FDA, which typically follows the recommendation.

Any time it approves or authorizes a vaccine, the FDA releases an analysis of the clinical trial data that the company has submitted. What the FDA found in the trial data looked good.

“There were no specific safety concerns identified in subgroup analyses by age, race, ethnicity, medical comorbidities, or prior SARS-CoV-2 infection,” the analysis said.

In a briefing document, the FDA said that it has reviewed the data for the vaccine and has determined that it is “consistent with the recommendations set forth in FDA’s guidance Emergency Use Authorization for Vaccines to Prevent COVID-19.”

Seems to work against variants

The Johnson & Johnson Covid-19 vaccine seems to work better than initial data showed against the virus variant first identified in South Africa.

The variant, which is thought to be more contagious, currently makes up the majority of cases in South Africa and has been found in several countries now, including in the United States.

According to the FDA analysis, the vaccine showed a 64% efficacy rate in South Africa. That’s seven points higher than the interim data that was released by the company in January. Since that time, J&J did some additional sequencing of the cases in the study, and determined that more of them were caused by a variant that could be included in its analysis. Nearly 95% of the cases in the study came from the variant, according to the addendum to the FDA analysis.

“The fact that the numbers came up a little bit, once they fully analyzed the data from the time of the initial press release, shows that it’s not that different against the South African variant,” said Dr. Philip Grant, who was the lead investigator on the Stanford University arm of the J&J vaccine trial. “I think it’s going to have to be looked at more carefully, in terms of which vaccines are most effective in different locations.”

The vaccine has a 72% efficacy rate in the US and a more than 68% rate in Brazil at protecting people from mild to severe/critical disease.

The vaccine offered nearly 86% protection against severe forms of the disease in the US, nearly 82% in South Africa and nearly 88% in Brazil.

Current Covid-19 vaccines made by Pfizer and Moderna are also thought to have good efficacy against the variants.

Experts have said variants may fuel a surge of cases in the spring in the US, and say that’s one reason why it’s important to get as many people vaccinated as quickly as possible.

“We’ll be seeing how much of an impact the variants have and how best these vaccines can address them, whether it will be booster doses, or other vaccines,” Dr. Aditya Gaur said, a co-lead investigator on the J&J trial at St. Jude in Memphis. “But I think one could not have asked for better from this first round of vaccine development from a standpoint of how quickly it has happened and how quickly it has started to roll out around the world.”

May prevent asymptomatic infections

The briefing document also hints that the J&J vaccine may prevent Covid-19 infection without symptoms starting at about four weeks.

A January study from the US Centers for Disease Control and Prevention have shown that most coronavirus cases are spread by people without symptoms. If a vaccine prevented asymptomatic infection, it might help reduce opportunities to transmit the disease – not just keep the vaccinated from getting sick.

The clinical trial looked for asymptomatic infections among the volunteers at several points after they had been vaccinated. The trial found that the vaccine had “modest” protection against asymptomatic infection from day one through day 29, but after that, it seemed to offer protection.

When the volunteers were checked for coronavirus antibodies at 71 days after they had gotten the vaccine, it seemed about 74% effective against asymptomatic infections.

“The news about asymptomatic infectious is very encouraging, with all the caveats,” said Grant.

The document says these findings should be “interpreted with caution” and additional research is needed, since the follow-up time is limited and the number of volunteers in this sample was comparatively small, so “definitive conclusions cannot be drawn at this time.”

Gaur said there is definitely a “signal here to see that there is efficacy of the vaccine against asymptomatic infection,” and he agrees it requires more follow-up studies.

A ‘favorable safety profile’

The analysis of safety data through January, found that the most common side effects associated with the vaccine were pain at the injection site, headache, fatigue and muscle pain.

There appeared to be more incidents related to blood clotting and ringing in the ears among those who received the vaccine compared with those who didn’t, but the FDA notes, “Data at this time are insufficient to determine a causal relationship between these events and the vaccine.”

Overall, non-fatal serious adverse events were infrequent, according to the briefing document, and there were no reported cases of anaphylaxis following vaccination.

With the Moderna and Pfizer Covid-19 vaccines, there have been a handful of severe allergic reactions, but this has been an extremely rare outcome. For example, in the first week of the Pfizer vaccine rollout, there were only 29 cases out of 1.9 million doses administered, according to the US Centers for Disease Control and Prevention.

As of February 5, there were seven Covid-19-related deaths in the placebo group in the J&J trial and no Covid-19-related deaths in the vaccine group.

The experts think this analysis is a good sign that the US could have another vaccine soon.

“I would be very surprised if they don’t approve this,” said Dr. Jeffrey Carson, the lead investigator for the Rutgers arm of the J&J vaccine trial. “The safety parameters look really good and the overall efficacy is over their criteria of 50% without a lot of serious side effects.”

And what that means, the experts said, is that people should get a Covid-19 vaccine – any vaccine that’s available – as soon as they can.

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“Given the effectiveness data that’s being shared with the vaccines that are available, in assuming this one gets approved, what we all should be seeking is a vaccine, not trying to look at, which one’s better because it’s just very, very nuanced,” Gaur said. “They’re all giving protection against the severe spectrum of the illness.”

CNN’s Jacqueline Howard contributed to this report