Johnson & Johnson said its single-dose vaccine was 72 percent effective in preventing COVID-19 in the U.S., but a lower rate of 66 percent was observed globally in the large trial conducted across three continents and against multiple variants.

In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe COVID-19 was just 57 percent in South Africa, where a particularly worrying variant of the novel coronavirus is circulating.

Following are initial reactions to the report:

Dr. William Schaffner, professor of infectious diseases at the Vanderbilt University Medical Center:

“We’re trying to get to 80 plus percent of people vaccinated in order to generate the herd immunity; this vaccine would certainly help us get there,” he said. “Down the road we’re having to prepare people already. They may have to get a booster dose of a new vaccine at some point in the future. Because it’s this virus that’s playing the tune we’re having to dance to.”

Dr. Walid Gellad, a health policy associate professor at the University of Pittsburgh:

“Right now, any protection and additional vaccine is great,” Gellad said. “The ‘South Africa’ strain is still uncommon in the U.S. and obviously we would want to see higher efficacy, but the key is not only overall efficacy but specifically efficacy against severe disease, hospitalization, and death. It’s unlikely we’re going to completely eliminate COVID anytime soon, but the key is to make it a minor nuisance instead of a deadly disease. This is one shot in the arm and good efficacy. Great news.”

Glenda Gray, the joint lead investigator of the South African vaccine trial:

“I am overwhelmed by the fact that this vaccine protected against severe disease even in South Africa.”

Gray, who is the chief executive of the South African Medical Research Council, said this is by far the best vaccine for South Africa and can prevent a large number of hospitalizations and deaths in the country.

Linda-Gail Bekker, the other joint lead investigator on the vaccine trial in South Africa:

“We are hoping the vaccine could be approved in the country by mid February as the regulator has said it will fast-track the approval process.”