Bharat Biotech’s indigenous vaccine Covaxin induced immunity against covid-19 through antibodies as well as T-cells and was found to be safe with no serious adverse events during its first two stages of trial, a pre-print of the phase 2 study showed.
“It is hypothesised that the humoral and cell-mediated responses reported in this study may persist until at least 6-12 months after the second vaccination dose,” showed the trial report, which is yet to be peer-reviewed.
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Humoral immune responses are caused by antibodies, while cell-mediated responses are caused by T-cells, which are major components of the adaptive immune system whose roles include killing infected host cells, activating other immune cells, producing cytokines and regulating the immune response. They are the second level of the body’s immune system after antibodies that are meant to attach to the pathogen and stop it from infecting cells.
“BBV152 induced binding (to both spike- and nucleocapsid protein epitopes) and neutralizing antibody responses that were similar to those induced by other SARS-CoV-2 inactivated vaccine candidates,” the study showed, adding that a sizeable memory T-cell population was also observed three months after the second and final dose was given.
The vaccine was tested in 380 healthy children and adults as part of the phase 2 immunogencity study, with half of them getting a 3 microgram of antigen, along with adjuvant, and the rest getting twice that dose of antigen and the adjuvant.
The primary objective of the study was to determine seroconversion—how many of the participants showed antibodies in their immune system—while the secondary outcome was to determine the safety and side-effects.
Covaxin was shown to induce T-cell memory responses and showed the ability to make the body secrete spike-specific IgG antibodies. An inactivated vaccine is basically a dead coronavirus, with the company also using an adjuvant to boost the immune response.
A pre-print of the company safety data in phase 1 trials was also released last week. It showed that one of the nearly 300 participants who were part of the vaccine arms of the Covaxin phase 1 trial showed serious side-effect during the trial. The side-effect was deemed as not related to the vaccine, showing that the shots were safe to use.
The company said that the study had several strengths, including the fact that it enrolled participants with a wide range of ages and found no differences in immune responses across age groups.
Davinder Gill, a vaccine expert in the US, said in the phase 2 trial, Bharat Biotech seemed to want to fix the dose for its phase 3 trial and later, and found that the 6 microgram dose with the adjuvant was more effective at inducing the production of neutralizing antibodies.
“Compared to the data that I have seen in other phase 2 studies from AstraZeneca, Pfizer and Moderna, Bharat Biotech for sure put out a lot more data. They have looked at various ways of measuring antibodies and various ways to look at neutralizing antibodies. But on the flipside, instead of more data, I would have liked to see a phase 2 maybe in 1,000-1,200 subjects, particularly because they were expanding the age group from 18-55 to 12-65 years,” Gill said.
Bharat Biotech is currently conducting a phase 3 study of 26,000 participants to determine the efficacy of the vaccine.