Corbevax may still be one step away from being available as India’s first heterologous COVID-19 booster jab, but top virologists are already in favour of adopting it.
Virologists and public health experts say Corbevax, manufactured by Hyderabad-based Biological E Ltd, may be more effective as a booster because it is a recombinant protein subunit vaccine that stands on the same platform as the hepatitis shot, meaning it’s tried and tested.
On Saturday, the Drug Controller General of India (DCGI) approved the use of Corbevax as a booster dose for people earlier vaccinated with either Covishield, made by Pune-based Serum Institute of India Ltd, or Covaxin, produced by Hyderabad-based Bharat Biotech International Ltd.
The inclusion of Corbevax, which is currently used only for the 12-14 year age group, in the national immunisation programme as a booster depends on a final decision by the Union health ministry.
Biological E said the DCGI’s decision on approving Corbevax as the booster jab for those above 18 years, six months of administration of either Covaxin or Covishield, came after a careful review of clinical trial data.
The data showed that Corbevax as a booster triggered a robust immunogenic response and was found to be safe.
Findings from the clinical trial have not been published in a peer-reviewed journal yet and are not yet available in the public domain for scrutiny by the scientific community.
Until now, all citizens above 18 years of age are eligible for a booster jab provided they have completed nine months since their second dose. They can only be vaccinated with the brand they had been administered earlier.
Effective against Omicron
Biological E said in a statement that it had conducted a multi-centre Phase 3 placebo-controlled heterologous booster clinical trial on 416 volunteers aged between 18 and 80 years who had been previously vaccinated with two doses of either Covishield or Covaxin at least six months prior.
The booster dose of Corbebax increased the neutralizing antibody titers in the Covishield and Covaxin groups significantly when compared to placebo. The titer is a test that detects the presence and measures the amount of antibodies within a person's blood
In a subset of subjects evaluated for neutralising antibodies against the Omicron variant, which for several months has been the dominant SARS CoV 2 strain circulating globally, the Corbebax booster shot resulted in a significant increase in the antibody titers, Biological E said.
After the booster dose of Corbevax, neutralising antibodies against Omicron were observed in 91 percent and 75 percent of subjects who had received primary vaccination by Covishield and Covaxin, respectively, the company said.
Importantly, the Corbevax booster dose also resulted in significant cellular immune response, as indicated by cytokine expression analysis after stimulation of the T-cells, a type of immunity cells.
Combination promising
Experts, although they are not privy to the clinical trial data submitted to the DCGI, vouched for Corbevax as an effective booster jab.
“Studies in India and abroad have shown that mix-and-match use of COVId-19 vaccines is a good idea and I believe that a protein sub-unit based vaccine on top of an adeno-virus vector based vaccine (Covishield) and inactivated virus based vaccine (Covaxin) has very good potential,” said Dr Gagandeep Kang, senior virologist with Christian Medical College, Vellore.
Dr K Srinath Reddy, who is a member of the national task force on COVID-19 pointed out that protein sub-unit vaccines use a time-tested platform and are safe.
“During an advanced pandemic, immunogenicity markers are correlates of protection which can be used to compare efficacy against already approved vaccines, since placebo- controlled trials are very difficult to perform in a population which is no longer immunologically naïve,” he said.
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Senior virologist Dr Shahid Jameel, who is associated with the University of Oxford and Ashoka University, too, said mixing and matching of vaccines has proven to be effective.
‘Global new normal’
“We do need to understand that while immune responses may be slightly different based on population genetics, they are not going to be fundamentally different,” said Dr. Jameel. “COVID-19 has shown this and it is likely to be the global new normal if we are to produce and deploy vaccines quickly.”
According to immunologist Dr Dipyaman Ganguly, attached with the Council of Scientific and Industrial Research-Indian Institute of Chemical Biology, it may be a good idea to use a sub-unit vaccine in place of a live adenovirus vaccine (Covishield) if the former is equally effective.
Christian Medical College carried out a clinical trial using a heterologous booster in two combinations: Covaxin to those vaccinated with Covishield earlier and Covishield to those jabbed with Covaxin earlier.
The results, although not in the public domain yet, showed that the use of Covishield on those vaccinated with Covaxin earlier was found more effective than the other combination.
The results were discussed within the COVID-19 working group of the National Technical Advisory Group on Immunisation, a top advisory body on immunisation in India.
The apex drug and vaccine regulator Central Drug Standards Control Organisation (CDSCO) is yet to review the data.
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But, Kang, stressed that when using boosters, either the same one or a heterologous vaccine, keeping a close tab on post-administration data would be crucial.
“Unfortunately, that practice is not enforced strictly in India,” she said.
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