Following Monday’s news of AstraZeneca and Oxford University's announcement that their coronavirus vaccine was up to 90% effective in late-stage trials, top experts say the preliminary findings are good news but await further analysis.
“The interim analysis supports vaccine safety with no severe reactions to the vaccine and that is good news,” Dr. Andrea Cox, immunologist and professor of medicine at Johns Hopkins University School of Medicine, told Fox News in an emailed statement.
Likewise, Dr. Thad Stappenbeck of Cleveland Clinic’s Lerner Research Institute said there were “no significant safety concerns, which is also outstanding news.”
However, in AstraZeneca’s trial, participants who were administered a smaller dose and then a full dose one month later saw around 90% efficacy, while the rate dropped to 62% among other participants given two full doses a month apart. ("Efficacy" measures disease incidence among vaccinated participants.)
“It is not clear why the results suggest the vaccine is less effective when given at a higher dose,” Cox continued.
An AstraZeneca spokesperson elaborated on the findings to Fox News earlier this week.
“We are excited to see 90% efficacy from the half dose: full-dose regimen," Brendan McEvoy, AstraZeneca spokesperson, said. "We see a lot of merit in this regimen and we will now start discussions with regulators into incorporating this dose combination for further clinical investigation. We will continue to follow the science to better understand these data."
Stappenbeck advised against overinterpreting the 90% efficacy result at this point, saying the findings will have to be repeated in other trials to see if it holds up. Indeed, AstraZeneca said the preliminary results stemmed from about 11,600 people in the UK and Brazil, and trials continue in the U.S., Japan, Russia, South Africa and other places. The company expects to enroll 60,000 participants globally.
“It is simply too small of a group and may be a statistical anomaly,” Stappenbeck wrote.
Cox offered several possible explanations for the different efficacy rates from the dosing regimens. Maybe the higher dose results in unresponsiveness rather than the sought-after immune response to the spike protein, she said.
“Sometimes when a protein is present at high levels, the immune system responds by turning off rather than responding,” Cox wrote.
Finally, among other possibilities, she theorized the higher efficacy from the half-dose/full-dose regimen could be due to differences in the vaccine population rather than true differences in the vaccine strategy, and, like Stappenbeck, said, “more analysis will be needed to determine what the results mean.”
Nevertheless, both experts pointed to the positive side that there are multiple potential vaccine candidates, which will be needed to meet global demand.
"These results suggest that we can add another vaccine to the armamentarium in the fight against COVID-19," Cox wrote.