COVID-19: Interim Results of COVAXIN’s Phase III Trials out, Claims 81% Efficacy

At a time when India has already entered the second phase of its COVID-19 vaccination drive, one vaccine in use – COVAXIN – produced by Bharat Biotech did not have efficacy data of its phase III clinical trial, a fact which attracted much controversy when this candidate was introduced in the vaccination drive.

However, the interim results of the vaccine’s phase III clinical trials were out on Wednesday and the company claimed that COVAXIN has an efficacy of 81%. The company has also claimed that the vaccine is effective against a more contagious strain of the virus which had emerged in the UK. The interim trial results, however, are yet to be peer-reviewed.

The phase III trial of the vaccine began in November last year and involved 25,800 participants between the ages of 18 and 98 years across 25 different sites. There were 2,433 participants who were above the age of 60 and those with comorbidities were 4,533 in number. The participants were divided into two groups — one which received the vaccine and other being a placebo group.

The interim analysis of this phase III trials consisted of 43 participants who contracted COVID-19. Out of these, seven participants received the COVAXIN dose and the remaining 36 were given a placebo. The formula used to calculate the efficacy rate is as follows—

36 (Who received a placebo) – 7 (who received the vaccine) X 100 = 80.55%

36 (placebo group)

The company said it plans to extend its interim analysis further for 87 cases which will further extend to 130 for a final analysis.

Commenting on the interim results, Dr. Randeep Guleria, the director of AIIMS said that for a statistically significant result a sufficient number of participants (around 130) were needed. He added that the results were encouraging and would help overcome the hesitancy of using this vaccine.

“To see efficacy, you need to have a sufficient number who get infected... and you don't know which group got the vaccine and which the placebo. When you have a sufficient number of positive cases, you can say efficacy is based on good data. After 43 events they broke the code (checked to see who got the vaccine and who the placebo) and, based on that, vaccine shows efficacy of around 81 per cent. But we need around 130-140 cases and then break the code to get real efficacy,” Guleria told NDTV.

Bharat Biotech said that a further analysis would be conducted for the vaccine. “An additional interim analysis is planned for 87 cases and the final analysis is planned for 130 cases. All data from the second interim and final analyses will be shared via pre-publication servers as well as submitted to a peer-reviewed journal for publication,” the company was quoted saying.

In India, COVAXIN and Covishield are being used for the vaccination drive. The latter is manufactured by the SII (Serum Institute of India) and was developed by Oxford University and AstraZeneca. Covishield has an efficacy of about 70%.