A new analysis of the AstraZeneca vaccine, led by the University of Oxford -- which developed the vaccine’s technology -- and published in Preprints with The Lancet, suggests a new dosing strategy, one that extends the time between the vaccine and the booster shot.

Unlike the Pfizer and Moderna vaccines, which have the second dose administered 21 days after the first, the AstraZeneca vaccine, in the analysis, showed it may work even better with a longer wait, up to three months, as the first shot provides significant protection.

Covering clinical trial data through December 7th, the analysis provides new insight based on 17,177 participants across the UK, Brazil and South Africa. There were 332 symptomatic cases of Covid-19 occurring 14 or more days after a booster dose, and 130 asymptomatic cases. For single shot participants, there were 88 symptomatic cases and 24 asymptomatic within 90 days after injection. The study researchers said they did look at why more participants contracted the virus after they received the booster. They said those who received the booster were older, more nonwhite than white, and were predominantly male.

The analysis shows that a single dose was 76% effective at preventing symptomatic infections, with no indication that the immune response was declining at the 90-day mark. It was not effective against asymptomatic cases. Waiting until at least 12 weeks before administering the booster shot increased efficacy to 82.4% compared to only 54.9% if the second dose was given 6 weeks or less later,

The AstraZeneca vaccine, developed at the University of Oxford, is an adenoviral vector vaccine. Here, engineered viruses act as an usher to carry specially designed genes with instructions to make the body’s cells produce coronavirus spike proteins. Encountering these spike proteins teaches the immune system how to fight them, allowing the body to respond more quickly and effectively if it encounters the actual coronavirus.

Safety data were not included in this analysis, but is available for the trial overall. It has already been granted emergency use approval in the UK with intervals of 4-12 weeks between shots.