CDC advisers to vote next week on who gets coronavirus vaccine first
An Oxford Vaccine Group researcher in a laboratory works on the coronavirus vaccine developed by AstraZeneca and Oxford University. John Cairns/University of Oxford/AP

More information and research is needed to understand the difference in efficacies of AstraZeneca vaccine dose schedules and whether a new trial is needed to check the efficacy of the lower dosage, World Health Organization officials said during a news briefing in Geneva on Friday.

“The first thing to say is, what we’ve seen is a press release,” said Katherine O’Brien, director of Immunization, Vaccines and Biologicals at WHO. “And what is really the next most important step is that the data really needs to be evaluated based on more than a press release.”

There is only so much that can be included in a release, she said, and it needs to be reviewed in terms of the data and questions asked about the data that may come up during the review.

“It’s difficult to weigh in on this,” O’Brien said. “I think what we can emphasize, though, is that from what we understand about the press release, there is certainly something interesting that has been observed, but there are many reasons that could underlie the differences that were observed.”

More information, including evaluations of the immune response in the trial, is needed, she said.

Dr. Soumya Swaminathan, WHO’s chief scientist, agreed with O’Brien, saying that everything that is known is from the news release, and it appears that less than 3,000 people were given the half dose, then full dose of the vaccine.

It is also understood that no one over the age of 55 was in that group. The group given two full doses were larger numbers and had different age groups.

“It’s very hard to compare these two groups and that I would say the numbers are still small to really come to any definitive conclusions,” she said.

“Now, of course, the advantage of using a smaller dose, particularly if you’re getting higher efficacy, is great and you can save on the vaccine and at the same time you are benefitting from higher efficacy, but I think it would be speculation at this point,” she said.

Swaminathan said that they have heard that AstraZeneca would like to do a full trial of the half dose full dose schedule, “if we are to explore this hypothesis of having perhaps a better efficacy with a lower dose, then it would need a trial.”

Remember: The US Food and Drug Administration requires a threshold of at least 50% efficacy. It is not clear if the FDA will authorize emergency use however.

AstraZeneca has not yet tested its half-strength dose in the US either. But on Thursday, a spokesperson for the company told CNN their aim was to include the half-strength dose regimen into their US trials, which currently has around 10,000 participants.

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