Covaxin, Covishield still potent against B.1.617 strain but produces fewer antibodies

Reduced antibodies not a cause of worry on efficacy against COVID-19, say experts

May 14, 2021 10:03 pm | Updated May 16, 2021 06:37 pm IST - NEW DELHI

A health worker shows Covaxin and Covishield vaccine. File

A health worker shows Covaxin and Covishield vaccine. File

Both Covishield and Covaxin, while effective at generating an immune response against the coronavirus, appear to generate only half as many antibodies against the B.1.617 strain, or the Indian strain, according to a series of early reports authored by scientists at the Indian Council of Medical Research (ICMR). Several scientists told The Hindu that this drop didn't diminish the fact that the vaccines continued to be potent tool against COVID-19.

Scientists at the ICMR-National Institute of Virology (NIV), Pune have since January been collecting samples from coronavirus-positive individuals and testing them for prominent variants — mostly the international variants of concern B.1.1.7 (UK variant), the B.1.351 (South Africa variant), the P2 (Brazil variant) and B.1.617 (Indian variant). Three related variants of the B.1.617 now make up an increasing proportion of cases in India.

Like their global counterparts, the two vaccines authorised in India, Covaxin and Covishield while made differently, were designed on the blueprint of the virus variant, called B1, that became the dominant strain in India by last April. With reports emerging from vaccine trials, across the globe, of certain mutations in the virus helping it evade immune systems and antibodies, several labs have been working to check the potency of vaccines against emerging variants.

When the NIV scientists tested the virus, bearing the B.1.617 signature mutations, on antibodies that were extracted from the blood serum of those with two doses of Covaxin, they found roughly 55% fewer antibodies than the antibodies generated against B.1.

When a similar study was done with those inoculated with Covishield, the Geometric Mean Titer (a proxy for the number of antibodies) with B.1 was 42.92 whereas with the B.1.617 it was 21.9, again roughly half.

On the other hand, when antibody levels were compared against the B.1.1.7 (UK strain), there was only a 6% reduction whereas against Brazilian strain (P2) there was again a 50% reduction.

Dr Samiran Panda, who heads the Epidemiology Division at the ICMR, Delhi, and was a co-author of the papers, said while the reductions were roughly on these lines, they showed that both Covishield and Covaxin were “almost similarly” protective against the B.1.617.

In those vaccinated, protection against a future infection isn’t solely determined by the number of antibodies and the extent to which they wax and wane over time, but also by the mobilisation of a class of defensive bodies called T cells, which it is believed direct a more specific kind of attack against the virus and destroys it unlike antibodies, which only block replicating virus cells.

“The antibody tests don't account for the T-cell response. Moreover these tests were done on a very small number of individuals. The average level of antibodies don't always capture the true range of antibody production,” he told The Hindu .

A two-fold reduction wasn't serious at all, said Rakesh Mishra, former Director, Centre for Cellular and Molecular Biology, Hyderabad, where independent studies are underway to estimate the neutralisation activity against various strains. “A ten fold or greater level of reduction may be important but then again different labs have varying approaches to conducting such tests,” he noted.

Vinod Scaria, who researches coronavirus variants at the CSIR-Institute of Genomics and Integrative Biology, said that while B.1.617 was found to be resistant to an antibody called Bamlanivimab, an antibody used for COVID-19 treatment, current data suggested it was much less of a threat than B.1.351 (the South Africa variant). Studies reported this month by microbiologist Ravi Gupta of Cambridge University, showed that the reduction in neutralisation involving B.1.617 was nearly four-fold in a set of people who had one dose of the Pfizer vaccine.

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