Error in Oxford-AstraZeneca Covid-19 vaccine dose: what does it mean?

 This week Monday, the world woke up to yet another Covid-19 vaccine news – the Oxford-AstraZeneca vaccine was reported to give highly promising results in both efficacy and safety. This was joyous after Pfizer and Moderna too announced promising results of their vaccine candidates. But on Thursday, multiple news rounded up in the US and UK questioning the data of the Oxford vaccine. But the questions weren’t regarding vaccine’s safety but efficacy. 

The trial data present three efficacy levels – overall efficacy of 70%, a higher of 90%, and a lower of 62%. This was because during the trial the participants were given different vaccine doses. Some of the volunteers were given half of the planned dose strength in error. But the low dose group produced better results. This has left experts around the world scratching their heads. 

The Covid-19 vaccine is to be given in two shots, four weeks apart, with the second shot as a booster to the first. Regulators were told of the error early on and they agreed to continue the trial. 

Around 3,000 trial volunteers were given a half dose of vaccine followed by a full dose four weeks later. This group showed a maximum efficacy of 90%. Further, 9,000 participants were given two full doses of vaccine a month apart. This group showed a 62% efficacy. AstraZeneca acknowledged both the findings and reported an average vaccine efficacy of 70% against coronavirus infection. This has led to confusion and doubts regarding vaccines. 

Prof. David Salisbury, the immunization expert, and a fellow of the Global Health Program at a think tank, Chatham House, said, “You’ve taken two studies for which different doses were used and come up with a composite that doesn’t represent either of the doses. I think many people are having trouble with that.”

The trial data is still preliminary and not final, just like Pfizer and Moderna vaccines. Once the firms have full data, they will be published in medical journals for peer review and public scrutiny. 

US regulator, FDA, says that for a vaccine to be effective during pandemics it must have an efficacy of 50%. AstraZeneca vaccine stands valid on these criteria even with its lowest value into account of 62%. So, basically, it doesn’t change anything regarding the promising candidacy of the Oxford-AstraZeneca vaccine. 

The Oxford researchers are meanwhile investigating as to why the lower vaccine dose receiving participants showed greater efficacy results.