The curious case of AstraZeneca-Oxford vaccine

Anglo-Swedish drugmaker AstraZeneca (AZ) had an eventful week during which it announced 63% efficacy rate for the vaccine it’s developing against the Covid-19 virus in partnership with Oxford University. The company announced that in a small subgroup of the trial participants the vaccine showed better efficacy when administered a half dose first and a full dose after a month. This announcement triggered a series of questions on the company’s trial protocol. However, on Thursday, the company started a new trial where it will administer a half and a full dose to a larger participant group. Divya Rajagopal explains the impact this will have on the approval timeline for the vaccine, which has implications for India too.WHAT IS THE EFFICACY OF THE AZ/OXFORD VACCINE?An interim analysis of 131 participants showed 70% efficacy when two different dosages were administered to two different groups of people. The larger group, which was given two full doses, showed 62% efficacy, while a smaller group of around 2,400 participants, which was given half and full doses, showed 90% efficacy.WHY DID THE VACCINE SHOW BETTER EFFICACY IN THE SUB-GROUP THAT RECEIVED HALF AND FULL DOSES?Sarah Gilbert, professor of vaccinology at the University of Oxford, said the reason is still unknown. She said a possible explanation could be that the immune system was reacting to the smaller dose as if it was fighting a real infection, leading to better response.WHY IS AZ STARTING A NEW TRIAL?AZ’s discovery that the vaccine works better with a smaller first dose was accidental. This was not part of the original trial protocol. It was an error on part of one of the trial contractors of Oxford University. The company will be starting trials afresh with a smaller dose fi rst to adhere to the best standards of critical trials.WHAT DOES THIS MEAN FOR SERUM INSTITUTE OF INDIA’S (SII) TRIAL?SII told ET that it will continue with the trial with two full doses. The AZ-Oxford vaccine is safe and effective and even the lowest efficacy rate is 60-70%, making it a viable vaccine, said SII. Efficacy could vary slightly in different age groups when given in different dosages. Adar Poonawalla, CEO of SII, said the Indian trials are running smoothly with strict adherence to all the necessary processes and protocols and the company was studying the data.WILL THE VACCINE LAUNCH BE DELAYED?AZ CEO Pascal Soriot said that the company does not expect the regulators to withhold emergency approval because of the new trial. The company can submit the efficacy data of 63% to get emergency approval as it is above the 50% that most regulators stipulate.

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