On Friday, the FDA committee will look at any potential safety issues. With the Moderna and Pfizer vaccines, for example, the committee asked questions about a handful of cases of severe allergic reaction to those vaccines. Severe adverse reactions were extremely rare.
The committee will also look at how effective the vaccine is. According to Johnson & Johnson's interim results, the data showed the vaccine was 66% effective in preventing moderate and severe disease. The vaccine is 85% effective overall at preventing hospitalization and 100% at preventing death in all regions where it was tested.
Its efficacy against moderate and severe disease ranged from one country to another: 72% in the US, 66% in Latin America, and 57% in South Africa. This was measured starting one month after the shot.
The differences in regional effectiveness may in part be due to the number of variants in circulation, experts said.
In the South African arm of the clinical trial, the majority of the cases were due to a variant known as B.1.351, which is more transmissible and carries mutations that make it less susceptible to the antibody immune response -- including antibodies that would be prompted by vaccination.
While the Pfizer vaccine showed an efficacy of 95% at preventing a symptomatic Covid infection after a person got two doses and the Moderna vaccine was 94.1% effective, scientist said it's not fair to compare vaccines, since they weren't tested against one another.
The Pfizer and Moderna vaccines, with this almost identical efficacy, were tested at about the same time. The J&J vaccine was tested a few months later, when there were more variants circulating.
"I think in the end, we don't know whether one is better than the other," Carson said.
Dr. Aditya Guar, one of the investigators with the St. Jude arm of the trial, said people need to understand that the J&J vaccine does its job very well.
"It's the outcome of preventing hospitalization and death that is important, and for that, it's complete," Guar said. "It is effective with one dose of the vaccine and it works."
Carson said patients and friends have been asking him if they should take the J&J vaccine when it is available.
"My advice to all my patients and to all my friends will be to get the first vaccine you can get. That's what matters the most, to get protected," Carson said.
All the vaccine makers are looking into whether a booster dose could provide better protection against coronavirus variants. J&J also has an ongoing late stage trial testing a two-dose vaccination program; the company is expected to have those results in the second half of 2021.
What Happens Next
Johnson & Johnson says it's confident about its single-dose vaccine candidate.
"The Company's EUA submission is based on topline efficacy and safety data from the Phase 3 ENSEMBLE clinical trial, demonstrating that the investigational single-dose vaccine met all primary and key secondary endpoints," a J&J spokesperson said in an email to CNN. "A one-dose vaccine is considered by the World Health Organization to be the best option in pandemic settings, enhancing access, distribution and compliance."
If the committee recommends an emergency use authorization of the J&J vaccine, the FDA will next decide if it wants to accept that recommendation. It usually does, and it could make its decision almost immediately, as it did with the Pfizer and Moderna vaccines.
Next, the US Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices will meet to discuss whether the vaccine should be given to Americans, and if so, this committee helps prioritize who should get the vaccine first. The committee has an emergency meeting scheduled for February 28 and March 1.
For Pfizer, the process took a little over three weeks. For Moderna, it was a little more than two.
Vaccinations could start shortly after. Johnson & Johnson's vaccine is expected to be easier to distribute and would require only one shot.
"If you think about it on a population basis, the J&J vaccine can offer more protection," said Dr. Philip Grant, a lead investigator for the J&J trial at Stanford University Medical Center. "You know if you give 10 shots of the J&J vaccine, that's protection for 10 people. Ten shots of Pfizer or Moderna is protecting five people. You know, even short term, it's going to have a huge role in the United States."
Push for More Doses
Still, questions remain about how many doses will be available. When asked, the company would not directly address the specific week-to-week production numbers. The US government has ordered 100 million doses to be delivered by June and J&J told CNN it can meet that commitment.
The company has been wrestling with upping its production, and the Biden administration has been keeping close tabs on the manufacturing, saying it's doing "everything we can" to accelerate the delivery schedule.
"The production of our vaccine is a highly complex process that requires very particular capabilities and experiences," according to the prepared remarks from Johnson & Johnson's Nettles. "As a result, there are significant challenges inherent in scaling manufacturing output and accelerating the timeline needed for a COVID-19 vaccine."
Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases and chief medical adviser to the White House, said Monday that more doses will come down the road.
"There will not be a lot of doses right on the heels of the EUA, but that will accelerate as we get into the months towards the contractual arrangement of when 100 million doses will be given," said Fauci.
It's also not clear who could be in line for the vaccine. Andy Slavitt, a senior adviser to the White House coronavirus response team, said Monday that the federal government will wait on a decision from the FDA and the guidance from the CDC committee.
Fauci said the FDA may find information in the trial data that would suggest the best strategies for distributing it.
"In the data there may be hints about just how this would be used most appropriately and most effectively. When we find that out, then the policy of the distribution would become much more scientifically based," Fauci said.