A medic prepares a dose of the Covaxin vaccine candidate at a hospital in Mumbai. Photo: PTI/Mitesh Bhuvad
New Delhi: Hyderabad-based Bharat Biotech has received the nod to give a third dose of its COVID-19 vaccine candidate Covaxin – six months after the second dose – to those who participated in clinical trials, to see if this could boost the body’s immunity against the novel coronavirus for a longer period.
The subject expert committee (SEC) of the country’s top drug regulator, the Central Drugs Standard Control Organisation, approved this proposal in a meeting held on March 23, according to Indian Express.
The SEC agreed with the pharmaceutical company’s proposal that the booster dose study should be conducted in participants of its phase 2 clinical trial, who received two shots of Covaxin containing 6 mcg of an inactivated SARS-CoV-2 virus. The booster dose will be given six months after the participants had received their second dose. According to the Indian Express, the vaccine candidate’s phase-2 clinical trial had taken place between September and October 2020, meaning the third dose could be given to some participants in April and May.
The SEC’s minutes note that Bharat Biotech should follow up with the subjects for “at least for six months after the third dose.”
“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.
The Indian Express report noted that around 190 participants had received 6 mcg strength of Covaxin in phase 2 trials. “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 English daily.
The results will then be analysed if Covaxin’s protection lasts longer when given in a three-dose regimen, spaced out over seven months. “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,” Indian Express said.
Bharat Biotech said last month that interim data from late-stage clinical trials showed that its vaccine candidate had an efficacy of 80.6% after two doses. It is one of two vaccine candidates – the other being Oxford-AstraZeneca’s Covishield – that is being administered in the country.
While the world’s hope to put an end to the pandemic are pinned on immunisation, it is yet unknown how long immunity provided by vaccines could last. Studies have already shown that acquired immunity against coronaviruses may not last longer than a year, and there have been several cases of reinfection.
As The Wire Science has reported, even before vaccines were rolled out, experts had begun suggesting that if reinfection is common, it may become necessary for seasonal vaccination shots.
If the results of Bharat Biotech’s new proposal demonstrate that the third dose could provide a greater period of protection, vaccination drives against COVID-19 would become “more affordable and less cumbersome in the long-term”.
The Hyderabad-based company’s proposed dosing schedule is similar to that of several vaccines given to children, where the third dose is given after an interval of around six months from 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,” the unnamed source told Indian Express.
Vaccine experts that the Indian Express spoke to welcome the development as a positive step towards understanding how vaccinations against COVID-19 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, a professor at Christian Medical College in Vellore.
Massachusetts-based vaccine expert Dr Davinder Gill told the newspaper that some companies have already discussed 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,” Gill said.
Gill said that Bharat Biotech had tested a three-dose schedule for Covaxin during animal studies. “Could the booster dose in question be informed by pre-clinical studies? It certainly could be,” he said.
During the same meeting, the SEC also approved the company’s proposal to “unblind” participants over 45 years in its phase 3 trial. This means that those who had received a placebo instead of the vaccine candidate would now be given the vaccine. The SEC asked the company to administer the vaccine free of cost to volunteers “as and when they become eligible for the vaccine in the national program”.
While the country has administered more than 6.87 crore doses of vaccine candidates, it is estimated that less than 10% are Covaxin.
The vaccine candidate’s rollout was mired in controversy, after CDSCO approved Covaxin ‘in clinical trial mode‘. This label was only removed last month, after Bharat Biotech released interim data from the clinical trials.
Meanwhile, Brazil’s health regulator Anvisa has denied Bharat Biotech’s request to import doses of Covaxin for use in the nation’s COVID-19 vaccination drive. The regulator said that the company did not present the minimum documents necessary to assess the risk of using the vaccine candidate in the Brazilian population.