Earlier this month, based on interim phase 3 data, Bharat Biotech had reported a 81% efficacy for Covaxin.
Data from a follow-up to the phase I trials of Bharat Biotech’s Covaxin shows that the immune response to the vaccine generated neutralising antibodies that remained elevated even three months after the receipt of the second dose.
A study by Bharat Biotech and Indian Council of Medical Research published in Lancet Infectious Diseases also noted that there was a better immune response—both in terms of antibodies and T-cell immunogenicity—when the gap between the two doses of the vaccine was 28 days (the regime followed in the phase 2 trial) as compared to 14 days (the regime followed in the phase 1 trial). Earlier this month, based on interim phase 3 data, Bharat Biotech had reported a 81% efficacy for Covaxin.
The first phase of the trial, apart from vaccine immunogenicity and reactogenicity, also looked at adjuvant selection—adjuvants are substances that enhance specific immune responses to a vaccine. Based on results from four groups administered any one of the four—3 microgram with adjuvant Algel-IMDG, 6 microgram with Algel IMDG, 6 microgram with Algel and 6 microgram of Algel adjuvant alone (the control group) – Algel IMDG was selected as the most effective adjuvant.
The 3-month (from second dose of phase 1 trial) also revealed that the T-cell memory response, that has emerged as a metrict for estimating Covid-19 vaccine success, was more pronounced of the ‘6 micrograms with Algel-IMDG adjuvant’ candidate. Also, day 56 serum samples from 38 participants in phase 2 trials who belonged to the group injected with this canidate effectively neutralised the UK variant of SARS CoV-2. This was, thus, preferred over the ‘3 microgram with Algel IMDG) candidate for phase 3 trials.
While the phase 2 data involved 380 adults and adolescents showed that the most common adverse event was pain at the injection site, and headache, fatigue and fever, a third of the ‘unsolicited’ (reported by the vaccine recipient outside the data collected per adverse event reporting protocol) adverse events—nine out of 27—were found to be related to the vaccine.
Also, against the backdrop of the controversy generated by the grant of the Indian equivalent of ‘emergency use authorisation’ to Covaxin pending phase 3 efficacy data, the study notes that no Covid-19 cases were reported in the test or control group in phase 2 and SARS CoV-2 testing of trial participants post vaccination was also not done in both phase 1 and 2. This would mean the data from the two phases would not have allowed for efficacy assessment.