NEW DELHI: Covaxin has shown an overall efficacy of 77.8 % against symptomatic Covid-19, 93.4 % efficacy against severe disease and 65.2 % efficacy against delta variant of SARS CoV 2, the results of its phase 3 clinical trials conducted on nearly 26,000 individuals have shown.
There had been massive pressure on Bharat Biotech, which has developed the vaccine with support from the ICMR, to release full data of the efficacy trials carried out earlier this year. Covaxin is the only fully homegrown Covid19 vaccine being used in India's Covid 19 vaccination drive and it had received regulatory approvals before completing phase 3 trials in January.
Bharat Biotech has now released the full data from the late-stage trials of Covaxin, a whole inactivated virus-based vaccine, on the pre-print server medrxiv, which are based on accruing 130 confirmed Covid 19 cases, 106 in the placebo arm and 24 in the vaccine group.
“BBV152 (Covaxin) was immunogenic and highly efficacious against symptomatic and asymptomatic Covid19 variant associated disease, particularly against severe disease in adults,” the researchers associated with the company, ICMR and 25 sites where the trials were conducted and a US based independent consultancy firm said.
“Vaccination was well tolerated with an overall incidence of adverse events observed over a 65 median of days that was lower than that observed with other Covid19 vaccines
Importantly, said the study, the results also showed 63. 6 % effectiveness against asymptomatic cases, which experts said was crucial to cut down the community spread of Covid19 over a period of time.
“In my view, the most remarkable part of the study was division of the participants in three groups, one of whom was followed for asymptomatic cases—something that most other mainstream vaccines had not done in their clinical trials,” said Rajeev Jayadevan, clinician, medical researcher and former president of the Indian Medical Association.
It is particularly significant, he said, as it gives the assurance that those fully vaccinated, may be far less likely to be carrier of infections.
“Such an assurance is helpful in workplaces among others and in the long run will curb the spread of the disease in the community as the percentage of vaccinated population grows,” added Jayadevan.
The study meanwhile said that there were 16 cases who met the severe symptomatic Covid-19 cases definition and all but one of whom were in the placebo group, resulting in a vaccine efficacy of 93·4% against severe disease.
There were 15 deaths in the study, none of which were considered by the investigators to be related to the vaccine or placebo; six deaths were reported to be related to Covid. In the vaccine recipients, there were five deaths all due to causes unrelated to vaccination-cerebellar haemorrhage, haemorrhagic stroke, ovarian cancer with metastasis, sudden cardiac death, and Covid19.
Ten placebo recipients died, also from unrelated conditions: alcohol overdose, myocardial infarction, cardiac arrest with underlying hypertension, five from Covid 19 and two which remain to be determined.
Overall, as per the analysis, incidence rates of adverse events were lower after the second dose than the first, and tended to be slightly higher in the vaccine group than the placebo group.
“However, all incidence rates were low, with only 12·4% reporting any solicited adverse events,” the study said.
In the study, a total of 79 variants were reported from 16,973 samples, 18 in the vaccine and 61 in the placebo group.
Among 50 delta (B.1.617.2) positive-confirmed cases, which is now the most dominant strain of SARS CoV2 in India, 13 and 37 participants were in the vaccine and placebo arms, resulting in vaccine efficacy of 65·2%.
Significantly, in breakthrough symptomatic delta variant infections, based on Ct values, the viral load in the vaccine arm was significantly lower than the placebo arm, the analysis has said.