What the latest Johnson & Johnson COVID vaccine data really means

Some have raised concerns that one of Johnson & Johnson's previously reported vaccine data points -- a 66% global efficacy in preventing moderately symptomatic disease -- doesn't seem as impressive as figures reported by Pfizer and Moderna, which exceeded 90% efficacy at preventing symptomatic COVID-19. But experts are quick to note that it may not be the best comparison: The Pfizer and Moderna clinical trials didn't take into account new variants and still had 100% effectiveness against hospitalizations and deaths.

"This is a very different trial than the trials that were done last fall," said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center and a lead researcher for the Johnson & Johnson vaccine. "We live in a much more complicated pandemic today."

While Pfizer and Moderna are conducting further research on their vaccines' efficacy against variants -- or if a booster will be required -- Barouch emphasized that the Johnson & Johnson vaccine has a leg-up in terms of its data, because it's the only one so far that's been tested against variant strains.

"Overall, the vaccine provides very robust protection throughout the world, including against the worrisome viral variants that we've been hearing so much about," Barouch added.

For many clinicians, the Johnson & Johnson vaccine performs best in what are the most important cases: severe illness that otherwise could lead to hospitalization -- or even death. So while protection from moderate cases may be less robust, a newly reported 100% protection against deaths and hospitalizations is "huge," said Dr. Darien Sutton, an emergency medicine physician and ABC News contributor.

"Knowing that this will help decrease the stress on hospital health care systems is, really, really great," he added.

Dr. Paul Goepfert, director of the Alabama Vaccine Research Clinic, also emphasized the nuances in dissecting the data, underscoring the reduction in severe cases as key.

"Severe COVID and death are the main things you want to protect against," he said, "because that's most important in terms of helping people and keeping hospitalization rates down -- and getting us back to normal."

In addition to limiting severe cases of COVID-19, Johnson & Johnson's vaccine is showing, according to the preliminary analysis, 74% protection against asymptomatic disease, which could help mitigate transmission. More research in this area is needed, but the data so far, according to Barouch, is "very promising."

Beyond the numbers, experts say the Johnson & Johnson vaccine has some significant advantages over the Pfizer and Moderna vaccines -- and not only because it requires a single dose, boosting convenience. Another advantage is its storage, as the vaccine can be kept for at least three months in normal refrigerators.

"That gives us the opportunity to put it in our primary care offices, pharmacies and community health centers, which translates into getting more people vaccinated," said Dr. Simone Wildes, an infectious diseases specialist at South Shore Health outside of Boston.

The FDA independent advisory committee plans to meet on Friday to review the Johnson & Johnson data and conduct a non-binding vote on whether to recommend it for emergency use. If endorsed by the FDA, the vaccine could be granted authorization as early as Friday evening, after which Johnson & Johnson forecasts 20 million doses could ready by the end of March, and 100 million by the end of June.

"It's definitely one more weapon in our arsenal to fight against COVID," said Dr. John Brownstein, chief innovation officer for the Boston Children's Hospital and professor of epidemiology at the Harvard Medical School. "These are all incredible vaccines. When it's your turn, you should take whichever one is offered."

Eric Silberman, M.D., a resident physician in internal medicine at Northwestern Memorial Hospital, is a contributor to the ABC News Medical Unit.

ABC News' Dr. Raehannah Jamshidi, Dr. Maia Ou and Dr. Abarna Ramanathan contributed to this report.