AstraZeneca Vaccine Can Slow the Spread of COVID, and Delayed Second Dose Works, Oxford Data Shows

According to a study in The Lancet , Britain's decision to delay the second shot of the AstraZeneca-University of Oxford coronavirus vaccine is effective at preventing symptomatic infection for three months after a single dose, reports CNBC . "Vaccine efficacy after a single standard dose of vaccine from day 22 to day 90 post-vaccination was 76 percent . . . and modeled analysis indicated that protection did not wane during this initial three-month period," the study said. The rate of effectiveness increased to 82.4 percent when there was at least a 12-week interval before the second shot — and when the second shot was administered less than six weeks after the first, the efficacy rate was 54.9 percent. "These analyses show that higher vaccine efficacy is obtained with a longer interval between the first and second dose, and that a single dose of vaccine is highly efficacious in the first 90 days, providing further support for current policy," the report declared. Based on weekly swabs from volunteers in the U.K. study, the investigators further observed a 67 percent reduction in virus transmission after the first dose of the vaccine. Britain also is delaying the second shot of the Pfizer-BioNTech vaccine, although the vaccine makers insist there is no data to support such a policy.