AN EXPERT panel of the country’s top drug regulator has allowed Bharat Biotech to administer a third dose of Covaxin to some of the volunteers in its ongoing clinical trials of the Covid vaccine. The approval, a result of the Hyderabad-based vaccine maker’s proposal to use an additional booster dose, would allow it to test the ability of Covaxin to prompt an immune response that could last a few years, The Indian Express has learnt.
In response to the proposal, the regulator’s Subject Expert Committee (SEC) recommended that the booster dose study be conducted in phase 2 clinical trial participants who received two shots of Covaxin containing 6mcg of the killed SARS-CoV-2 virus. The booster dose is to be given six months after the participants had received their second dose in the trial, which had taken place between September and October 2020.
Bharat Biotech is also to follow up these participants “at least for six months after the third dose,” according to minutes of the SEC’s meeting dated March 23.
“Further, the firm should present the details of the primary and secondary objectives and various assessments to be carried out in the subjects. Accordingly, (the) firm should submit the revised clinical trial protocol for evaluation,” the SEC added in its recommendations.
Around 190 participants had received the 6 mcg strength of Covaxin in the phase 2 trials, according to data published by the company.
“Now, these participants will further be divided into two groups, where one of the groups will receive the third booster dose,” a source, who is aware of the development, told The Indian Express.
The two groups will then be studied to see how much longer Covaxin’s protection lasts when given in a three-dose regimen spaced out over seven months, the source said. It also will help it understand whether the third dose could help build stronger Memory T Cells in the body for a better protective response in case of future infections, the source said.
The move to test a third dose would be beneficial if the results show the vaccine’s ability to protect people from developing mild to severe symptoms of Covid for years. This would make vaccination against Covid more affordable and less cumbersome in the long-term, as some companies have already begun discussing the possibility of people having to come back for annual shots to maintain immunity.
Bharat Biotech plans to test a dosing schedule similar to those used in several vaccines given to children — the second dose given a month after the first and the third dose around six months after the second.
“In children, with vaccines for diseases like Hepatitis B, you give a long gap (after the second dose) and then a booster so that you have long-term or lifetime immunity,” said the source. “This is to understand whether a third dose can give long-term immunity and also whether it can have a booster effect on the memory cells,” sources said.
Vaccine experts feel the development is a positive move to help understand how vaccinations against Covid can be improved. “Since antibody titres (the level of antibodies) decline in infection in six months, it is worth seeing what happens with vaccinations and with boosting,” said Dr Gagandeep Kang, Professor, Christian Medical College-Vellore.
“Companies like Pfizer have already been talking about the possibility of an annual booster shot. While everyone has been caught up with aspects like the efficacy of Covid-19 vaccines, the million dollar question is what is the duration of protection,” said Massachusetts-based vaccine expert Dr Davinder Gill.
According to Gill, Bharat Biotech has a potential reason to study the effect of Covaxin in three doses, considering that it had tested a three-dose schedule during its animal studies. “Could the booster dose in question be informed by pre-clinical studies? It certainly could be,” he said.
During its March 23 meeting, the SEC also recommended that Bharat Biotech “unblind” participants over 45 years in its phase 3 trial who had received a placebo instead of Covaxin. It added that the company should “offer to administer the vaccine free of cost as and when they become eligible for the vaccine in the national program,” according to the minutes.
The fresh clearance for a third dose has come less than a month after the SEC recommended the removal of the “clinical trial mode” label attached to the emergency authorisation of Covaxin. This had followed the vaccine maker’s announcement on March 3, based on interim data from late-stage clinical trials, that the vaccine had an efficacy of 80.6 percent.
As on Thursday, around 6.60 crore doses of Covid vaccines — Covaxin and Serum Institute of India’s Covishield — had been administered across India, of which 61.36 lakh were of Covaxin, according to the government.
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