Johnson & Johnson (J&J) and Novavax separately released preliminary clinical trial data on their Covid-19 vaccine candidates, setting the stage for the companies to seek FDA's authorization for the experimental vaccines. Here's what the data shows—and what it could mean for America's coronavirus epidemic, according to experts.

Related: The U.S. Covid-19 vaccination scenario planning guide

What the data says on J&J's vaccine

During a press conference held Friday with NIH, which helped conduct J&J's Covid-19 vaccine trial, J&J released a preliminary analysis of its Phase 3 clinical trial data for its Covid-19 vaccine candidate. J&J's vaccine candidate is different than the two Covid-19 vaccines currently authorized for use in the United States—which are manufactured by Pfizer and BioNTech, as well as Moderna—because J&J's vaccine requires patients to receive just a single dose, rather than two. In addition, J&J's vaccine uses an adenovirus instead of messenger RNA to trigger an immune response to combat the novel coronavirus.

To test the vaccine candidate's effectiveness and safety, J&J and NIH launched a clinical trial with a "diverse and broad" patient population, the company said. Researchers enrolled in the trial 44,325 participants from across the world, including 44% of participants from the United States, 41% from Central and South America, and 15% from South Africa. Among the trial's participants, 59% were white, 45% Hispanic or Latinx, 13% were Black, 6% were Asian, and 1% were Native American. Some of the participants had underlying health conditions, including HIV, hypertension, Type 2 diabetes, and/or obesity.

According to the preliminary analysis, J&J's vaccine candidate was 66% effective at preventing both moderate and severe Covid-19 cases 28 days after trial participants received their vaccinations. When looking only at severe cases of Covid-19, the vaccine was 85%, the analysis found.

In addition, the analysis showed J&J's vaccine candidate prevented hospitalizations or deaths related to Covid-19. According to the analysis, no deaths related to Covid-19 occurred among participants who received the experimental vaccine, but five deaths linked to Covid-19 occurred among patients who received a placebo.

Paul Stoffels, J&J's chief scientific officer, said the preliminary analysis showed the vaccine candidate appeared to have a strong efficacy among participants regardless of their age.

However, the preliminary analysis showed that the vaccine candidate's efficacy varied based on geography. For instance, the analysis found the vaccine was 72% effective among clinical trial participants in the United States, but it was 66% effective among participants in Latin America. Further, the analysis showed that the vaccine candidate was just 57% effective in South Africa, where a new variant of the novel coronavirus, called B.1.351, has been circulating. Research suggests that variant is more transmissible than the original version of the novel coronavirus and more resistant to vaccines and treatments for Covid-19. On Thursday, U.S. officials announced the first known cases of the B.1.351 variant in the United States.

In terms of safety, the preliminary analysis showed fevers occurred in 9% of participants who received the vaccine candidate, and fevers of more than 104 degrees occurred in 0.2% of participants who received the experimental inoculation. The analysis also that showed one participant had a stroke during the trial, which led researchers to the pause the trial earlier this year. However, scientists ultimately determined that the stroke was not related to the experimental vaccine, Stoffels said. Overall, the analysis showed that serious adverse events were less common among those who received the experimental vaccine than among those who received the placebo.

J&J in early February expects to request an emergency use authorization (EUA) for its vaccine candidate from FDA. If the FDA grants the EUA, the company will be prepared to immediately ship out doses of the vaccine, though J&J did not offer details on how many doses would be available, STAT News reports.

According to the New York Times, federal officials familiar with J&J's production of the experimental vaccine has said the company might have seven million doses ready to ship immediately if it receives an EUA and about 30 million doses available by early April.

What the data says on Novavax's vaccine

Separately, Novavax on Thursday released preliminary data from its Phase 3 clinical trial for its Covid-19 vaccine candidate, which requires patients to receive two doses and uses recombinant nanoparticle technology to activate an immune response against the novel coronavirus. For the trial, Novavax enrolled 15,000 participants from the United Kingdom between the ages of 18 and 84. According to Novavax, 27% of the participants were older than 65.

Novavax said the preliminary data showed its experimental vaccine was 95.6% effective at preventing Covid-19 caused by the original version of the novel coronavirus and 85.6% effective at preventing Covid-19 caused by a more-transmissible variant first identified in the United Kingdom, called B.1.1.7, which has now been detected in more than 40 countries, including the United States. According to Novavax, the preliminary data showed 62 cases of Covid-19 occurred in the trial, with 56 of those cases occurring among participants who received a placebo and six among participants who received the vaccine candidate.

In addition, Novavax said preliminary data from a separate Phase IIB clinical trial being conducted in South Africa showed its vaccine candidate was 49.4% effective at preventing Covid-19 caused by the B.1.351 variant.

Novavax said it is developing booster shots for its vaccine candidate aimed at offering better protection against the new coronavirus variants, and it plans to begin testing those shots in people during the second quarter of 2021.

Currently, Novavax executives said they're in talks with U.S. regulators to determine whether the data the company's gathered so far from its U.K. and South Africa trials is adequate for the company to apply for an EUA from FDA. According to Politico, Novavax also is continuing to enroll participants in a U.S.-based trial on the vaccine candidate.

What the data means for America's coronavirus epidemic

The data comes as U.S. officials are looking to speed up America's slower-than-expected rollout of Covid-19 vaccines. CDC data shows that, as of Thursday morning, the federal government had distributed about 48.4 million doses of the United States' two authorized Covid-19 vaccines, which each require that patients receive two doses of the inoculations a few weeks apart. According to CDC's data, a total of about 26.2 million doses of the vaccines had been administered to Americans as of Thursday morning. Of those, about 21.7 million Americans had received "one or more doses," and about 4.3 million had received two doses, the data shows.

According to STAT News, the preliminary data from both J&J and Novavax shows their vaccine candidates each have efficacy levels above the 50% threshold originally established by FDA for receiving an EUA from the agency, but their efficacy levels are lower than the 90% or higher efficacy levels seen with America's currently authorized Covid-19 vaccines. As a result, some observers felt the data on J&J's and Novavax's experimental vaccines was disappointing.

For example, Eric Topol, director and founder of the Scripps Research Translational Institute, called J&J's clinical trial results "disappointing," but he also noted that the vaccine prevents hospitalizations and deaths from Covid-19, which is valuable. J&J’s results also "reinforce[e] how lucky we were that the first two [authorized Covid-19 vaccines in the United States] were more effective," he said.

But other observers and stakeholders noted that J&J's one-shot vaccine presents an advantage, in that it can ensure people are vaccinated against Covid-19 more quickly. For instance, Stoffels told STAT News that "[i]n a pandemic, if you can, with a single-dose vaccine, very quickly eliminate the severe consequences of death, hospitalization, and severe disease, that's what's important for society."

Akiko Iwasaki, a virologist at Yale University, said it's difficult to compare the trial results from the United States' two authorized vaccines with this new data on J&J's vaccine candidate, because those trials also took mild Covid-19 cases into consideration, while J&J's trial only accounted for moderate to severe Covid-19 cases.

Still, Iwasaki called the data on both J&J's and Novavax's vaccine candidates strong. Further, Iwasaki said it's important that as many people get vaccinated as possible, because of persistently high numbers of new coronavirus cases and the lack of immunity among the population.

"We've got to get [a] dose to as many people as possible," Iwasaki said. "These variants that are more transmissible and potentially even more lethal are on the rise. I think time is really what we're fighting against" (Herper, STAT News, 1/29; Zimmer et al., New York Times, 1/29; Johnson/Achenbach, Washington Post, 1/28; Lim, Politico, 1/28; Hensley/Palca, NPR, 1/28; Novavax release, 1/28; New York Times, 1/29; "The COVID Tracking Project," The Atlantic, accessed 1/29; CDC data, updated 1/28).