A three-month interval between doses of the Oxford University-AstraZeneca vaccine resulted in higher vaccine efficacy than a six-week interval, reveals The Lancet study.

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According to the findings from a phase 3 randomised controlled trial, the first dose offered 76 percent protection in the three months between doses. The interval between doses can be safely extended to three months given the protection a single dose offers, which may allow countries to vaccinate a larger proportion of the population more rapidly, the researchers said. "Where there is a limited supply, policies of initially vaccinating more people with a single dose may provide greater immediate population protection than vaccinating half the number of people with 2 doses," said lead author Andrew Pollard from the University of Oxford, UK. "In the long term, a second dose should ensure long-lived immunity, and so we encourage everyone who has had their first vaccine to ensure they receive both dose," Pollard added.A

For the study, the team combined data from randomised controlled trials in the UK, Brazil, and South Africa, including more than 17,000 people. Participants either received two standard doses of the Oxford Covid-19 vaccine (8,597 participants) or a control vaccine/saline placebo (8,581).A

Looking at the interval between two standard doses and its impact on efficacy, participants who were given their doses 12 or more weeks apart had greater protection (81 percent, based on 8/1,293 cases in the Covid-19 vaccine group vs 45/1,356 cases in the control group), than people given their two doses less than 6 weeks apart (55 percent, based on 35/3,890 cases in the Covid-19 vaccine group vs 76/3,856 cases in the control group).A

Efficacy results were supported by immune response results in 18-55 year olds, which found that binding antibody responses were more than two-fold higher in the group having their two vaccines with a longer delay. Following a single standard vaccine dose, vaccine efficacy from 22 days to 3 months after vaccination was 76 percent (based on 17/9,257 cases in the Covid-19 vaccine group vs 71/9,237 cases in the control group), and modelling indicated that this protection did not reduce over the 3 months.