Oxford's COVID-19 vaccine reached 90% efficacy due to dosing error; here's how it happened

A “serendipity” of an error led Oxford University and AstraZeneca vaccine trails to reach 90% efficacy after researchers accidentally gave some participants half doses. Oxford University revealed on November 23 that its vaccine candidate developed with AstraZeneca had an overall efficacy of 70.4% but it could be nearly 90% when administered as a half dose followed by a full dose a month later. 

It is both a triumph but also a matter of disappointment because Pfizer-BioNTech and Moderna have already declared their respective vaccine candidates to be 95% and 94% efficient against COVID-19. However, Oxford and AstraZeneca’s vaccine is reportedly far cheaper and is comparatively easier to store and transport to even remote areas of the world. 

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How did the error take place?

However, as per the Guardian report, the executive vice-president of biopharmaceuticals research and development at AstraZeneca, Mene Pangalos explained that the reason researchers had the “half dose is serendipity”. As per reports, when the university researchers were giving out vaccine doses at the end of April when the Oxford-AstraZeneca partnership had just begun, they noticed some milder than expected side effects including fatigue, headaches or arm aches. 

Pangalos also said that when the researchers went back checked, they found out that the dose of vaccine was “underpredicted” by half. After finding out the error, the researchers still continued with the half dose along with administering the full dose booster shot at the scheduled time. As per reports, at least 3,000 were given a half dose of its COVID-19 vaccine candidate followed by a full dose at least four weeks later. 

This pushed the vaccine efficacy to 90%. Meanwhile, in another larger group, the volunteers were given two full doses a month apart and the efficacy was 62% that made the overall efficacy over 70%. However, scientists reportedly can still not fully derive the main reason behind the increased efficacy when vaccination is started with half doses. 

As per the same report, Professor Sarah Gilbert from Oxford University who led the research said that it may be that reduced doses trigger the immune system in a different manner. Meanwhile, the director of the Oxford Vaccine Group and chief investigator of the trial Professor  Andrew Pollard said that researchers do not know if its the difference in quantity or quality of immune response and informed that the matter will now be investigated by the team.

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