Leana Wen, a CNN medical analyst and former Baltimore public health commissioner, "when that's not a fair assessment to make."

It's very effective against severe disease

On Wednesday, the FDA released an analysis of vaccine clinical trial data submitted by Johnson & Johnson, saying the vaccine met the FDA's requirements for emergency use authorization.

"That's probably the most important part of this vaccine or any of the Covid vaccines is the protection against hospitalizations and severe disease and dying," said Dr.

Wen said what really matters is a vaccine's ability to prevent severe disease, and beyond that, disease that's severe enough that leads to hospitalization or even death.

"In this regard," she said, "all of the vaccines are essentially a hundred percent."

While preventing infections would be great -- and there is evidence Johnson & Johnson's vaccine is effective against asymptomatic infection -- its avoiding severe cases that will save lives.

Anthony Fauci told CNN the vaccine had "very good efficacy against severe disease," and that the results would have looked even better if it weren't for the fact it had to compete with the vaccines from Pfizer-BioNTech and Moderna.

"We would have said wow, a 72% effective vaccine that's even more effective against severe disease is really terrific," he said.

While it might be an easy point of reference, Wen said it's not correct to compare the Johnson & Johnson vaccine to its counterparts by Pfizer-BioNTech and Moderna.

That's not how this was done."

The vaccines were also tested at different times, she said, and different types of strains were more prevalent than others depending on the location.

There, the vaccine showed a 64% efficacy rate.

Offering protection against the variant could give the Johnson & Johnson vaccine a "slight edge," Wen said, since neither Pfizer's nor Moderna's vaccine was tested in that environment.