AstraZeneca vaccine more effective when 2nd shots delayed 3+ months, study finds

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.