One dose of the AstraZeneca-Oxford vaccine provided strong protection against COVID-19 in clinical trials when second doses were delayed by at least three months, according to a Lancet preprint published Feb. 2.
Researchers measured data from thousands of participants regarding the three months after the first dose was administered, not including an initial three-week period needed for protection to take effect. The findings suggest that a single shot of the vaccine was 76 percent effective.
Furthermore, the vaccine appeared more effective when the time between the two shots was longer than the intended four weeks. The vaccine was 82 percent effective for participants who got two standard doses at least three months apart, compared to 55 percent effective when doses were given within six weeks of each other.
At least three months between vaccine doses may be “optimal for rollout of a pandemic vaccine when supplies are limited in the short term,” the researchers wrote.
The study has not yet been peer reviewed.
The AstraZeneca vaccine has not been authorized in the U.S., and the data findings shouldn’t be generalized to other vaccines.
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