Reading the clues from Covaxin early trial data
Bharat Biotech, which is among the frontrunners in the race to develop a coronavirus vaccine in India, released new data from phase 1/2 clinical trials. The vaccine is still being tested for efficacy – whether it can prevent Sars-Cov-2 infections – but the data shows it is progressing well. A look at the key indicators and how it might compare with some other candidates.
Bharat Biotech’s coronavirus vaccine candidate, jointly developed with the Indian Council of Medical Research (ICMR), passed the two crucial tests in clinical trials – showing it was safe and triggered an immune response – according to early stage analysis released on Wednesday.
The Phase 1/2 data showed that levels of neutralising antibodies in those who received the vaccine -- called Covaxin -- were similar to those who recovered from a natural infection. This level was at its peak at 42 days after the second dose, with a dip seen at 104 days.
Among all participants in the early phase who received the vaccine, 98.3% “sero-converted” (that is, they developed an antibody response).
But how do these numbers compare with other leading vaccine candidates whose data has been released?
The comparison can be made in two ways: drawing parallels with other candidates that use the same method to train a person’s immunity, or by comparing some of the parameters with the leading candidates already approved.
Bharat Biotech’s Coovaxin is based on an inactivated virus, and for the first method of comparison, there are four others in late-stage trials that it can be compared. All four of these are being developed by Chinese companies but only one, Sinovac’s Coronavac, has carried out an analysis that can be picked up for comparison.
At the outset, it appears that the Indian candidate may be comparable or even slightly better than its rival on some parameters. When people were given both doses of Covaxin, 98.4% of them developed antibodies compared at day 56 to 100% at day 28 after the two-dose regimen in the Coronavac trial, according to phase 2 trial data released by both.
The difference was more stark when it came to how strong the level of antibody response was. In the case of Covaxin, volunteers showed levels similar to those who had a natural infection from Sars-Cov-2 and recovered. But in the case of Coronavac, this level was roughly a third of what was seen in recovered individuals.
To be sure, there could still be some variations in test methods used by researchers and the studies were held separately, in different populations, that do not lend to like-for-like comparisons. But the proportion of people who develop an antibody response and the comparison of antibody levels with recovered (convalescent) people are relative parameters that can be used to loosely compare vaccine performance.
Sinovac and Bharat Biotech both judged their vaccines on these parameters, while the three other inactivated virus platform candidates in late-stage trials (two of them are by Sinopharm and the third by Chinese Academy of Medical Sciences) have not compared antibody levels to convalescent patients.
While the Indian and the Chinese candidates have a platform overlap and both use a two-dose regimen, they also have some differences. The Chinese Coronavac, for instance, requires a booster shot at 14 days while the Indian one was at day 28.
The two vaccine candidates also use different adjuvants -- ingredients that are used to help create a stronger immune response. Coronavac uses aluminium, which is a commonly used adjuvant, while Covaxin incorporates a proprietary adjuvant called Algel-IMDG.
The second method of comparison is to take into account the number of antibodies developed after people were given the Moderna and Pfizer-BioNTech vaccines.
In Moderna’s case, 100% of the people developed antibodies and the levels were over twice as the levels seen in convalescent individuals. In case of the Pfizer and BioNTech inoculation too, 100% of individuals developed antibodies and this level was close to four times.
Both these numbers are far ahead of Covaxin and Coronavac.