The Reason A Delayed 2nd Covid Vax Shot May Mean Better Protection

This should allay concerns about those whose second vaccination was delayed due to weather or supply shortages and it it could make it easier to get more people their first shot. which could help slow the spread of variants. JL

Nature reports:

The two-dose vaccine developed by the University of Oxford, UK, and pharmaceutical firm AstraZeneca in Cambridge, UK, could be given to more people by lengthening the interval between jabs. For intervals greater than six weeks, the longer the gap between jabs, the better the vaccine protected against COVID-19. It was 55% effective in those who received their second dose less than 6 weeks after their first, and 81% effective in those whose second dose was more than 12 weeks after their first. The team also found that a single dose of the vaccine had an efficacy of 76% for the first 90 days after vaccination.

A widely used COVID-19 vaccine is more effective if the second of its two doses is given after a long wait rather than a short one — a finding that supports a decision by UK public-health officials to space out the doses.

The two-dose vaccine developed by the University of Oxford, UK, and pharmaceutical firm AstraZeneca in Cambridge, UK, could be given to more people by lengthening the interval between jabs. To test the efficacy of this strategy, Andrew Pollard at the University of Oxford and his colleagues examined clinical-trial data from more than 17,000 people, half of whom received the vaccine and the other half a placebo (M. Voysey et al. Lancet https://doi.org/fwk7; 2021).

The team found that, for intervals greater than six weeks, the longer the gap between jabs, the better the vaccine protected against COVID-19. It was 55% effective in those who received their second dose less than 6 weeks after their first, and 81% effective in those whose second dose was more than 12 weeks after their first. The team also found that a single dose of the vaccine had an efficacy of 76% for the first 90 days after vaccination.