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

The coronavirus vaccine, developed by Oxford University and AstraZeneca, achieved a 90% efficacy rate by accident owing to an error that led to some of the study participants receiving half doses.

A press note released by Oxford University on Monday, November 23, revealed that the COVID-19 vaccine being developed by it and AstraZeneca has shown 70% efficacy. Oxford-AstraZeneca further added that the inoculation could be around 90% effective under "one dosing regimen" when administered as a half dose followed by a full dose a month later.

Mene Pangalos, executive vice-president of biopharmaceuticals research and development at AstraZeneca told The Guardian that the clinical trials reached 90% efficacy by accident, thanks to the "serendipity" of an error.

Also Read: 'India, top priority': Serum Institute CEO Adar Poonawalla on COVID-19 vaccine distribution plan

Talking about its genesis, Pangalos said that when the (Oxford) university scientists were dispensing the vaccine at the end of April, around the beginning of Oxford and AstraZeneca's partnership, they observed some side effects such as headaches, arm aches, and fatigue which were milder than expected.

Thus, when "we went back and checked ... and we found that they had underpredicted the dose of the vaccine by half," he stated. Following this, the scientists, rather than restarting the trial, decided to carry on with the half dose and administer the full dose booster shot at the scheduled time.

Around 3,000 people were given the half dose followed by a full dosage four weeks later, with data exhibiting that 90% of them were protected. Meanwhile, in the larger group, who were administered two full doses, also four weeks apart, the efficacy rate was registered at 62%.

The researchers said they could not explicate why the half dose manifested better protection, but added it may be that it prompts the immune system differently.

Also Read: India may get Oxford University's coronavirus vaccine in Jan-Feb

"It could be that by giving a small amount of the vaccine to start with and following up with a big amount, that's a better way of kicking the immune system into action and giving us the strongest immune response and the most effective immune response," Prof. Sarah Gilbert from Oxford University, who led the research, told the publication.

Prof Andrew Pollard, director of the Oxford Vaccine Group and chief investigator of the trial, further added that what is unknown at the moment is whether the difference is in the quality or the quantity of immune response, and "that's something we're going to be digging into over the next weeks."

Meanwhile, the vaccine still needs to be given a go-ahead by the UK-based Medicines and Healthcare products Regulatory Agency.

Also Read: BREAKING: Oxford-AstraZeneca's vaccine shows 70% efficacy against coronavirus