The logo of Covaxin on Bharat Biotech’s website. Photo: Jernej Furman/Flickr, CC BY 2.0
New Delhi: Bharat Biotech’s Covaxin offers a lower level of protection against the delta variant of the coronavirus (B.1.617.2) compared to the original strain, as people who have received both doses of the vaccine are likely to have nearly three-times lower levels of neutralising antibodies.
These results were reported in a small study conducted by researchers at the National Institute of Virology (NIV), Pune; Bharat Biotech, Hyderabad; and the Indian Council of Medical Research (ICMR), New Delhi.
The study tested the efficacy of Covaxin against two variants: beta (B.1.351), first reported from South Africa, and delta. It included only 37 participants.
The preprint paper’s summary says the emergence of the B.1.617 lineage has created serious public health problems in India. “The high transmissibility … [of] this lineage … has led to [a] daily increase in the number of SARS-CoV-2 infections. Apparently, the sub-lineage B.1.617.2 has slowly dominated the other variants including B1.617.1, B.617.3 and B.1.1.7,” it reads.
The study evaluated the neutralisation potential of blood sera[footnote]Plural of serum[/footnote] collected from 20 patients who had recovered from COVID-19 – 17 had been infected by the ‘original’ B.1 strain and three by the B.1.617.1 strain – and from 17 people who had received both doses of Covaxin.
The sera were collected from the first group 5-20 weeks after the members had recovered from COVID-19, and from the second group 28 days the members had received both doses of Covaxin.
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The researchers found that the neutralisation titres (the measured antibody levels) dropped 3x in people vaccinated with Covaxin against the beta variant, and 2.7x in people vaccinated with Covaxin against the delta variant. The 3x and 2.7x are both relative to the vaccine’s protection against the original strain.
The neutralisation titres in sera collected from those who had recovered from COVID-19 dropped further – 3.3x against the beta variant and 4.6x against the delta variant.
In sum: the protection against the beta and delta variants drops less if a person has received Covaxin than if they have not. This is the basis on which the researchers have concluded that the vaccine offers some protection against the beta and delta variants.
Clinical studies conducted earlier have found that a higher concentration of antibodies is a good predictor of vaccine efficacy and greater protection against COVID-19.
“Although there is [a] reduction in neutralisation titres, the whole-virion inactivated SARS-CoV-2 vaccine (BBV152) [Covaxin] demonstrates protective response against B.1351 and B.1.617.2,” the preprint paper’s summary concludes.
Pragya Yadav of the NIV, and the first author of the preprint paper, told The Hindu that many other studies investigating the neutralisation potential of sera collected from people who were administered different vaccines have also used “only a small number of samples”.
However, this doesn’t change the fact that the study’s results – no matter how encouraging – are limited by its small cohort size.
The preprint paper has another significant issue. The authors have written that they don’t have “a conflict of interest among themselves”.
However, Bharat Biotech developed the vaccine; NIV isolated the virus that used in the vaccine; and ICMR helped Bharat Biotech test the vaccine. And all the authors are affiliated with these institutes.
As a result, all the authors have a conflict of interest.