The studies, published in Nature, covered Oxford-AstraZeneca vaccine, but not India’s indigenous Covaxin
An analysis of 183 of 358 people infected by the omicron variant of the novel coronavirus (SARS-CoV-2) in India showed 87 were fully vaccinated against COVID-19 while three had received three doses. Two persons were partially vaccinated while 23 were unvaccinated (16 were not eligible and the rest were not vaccinated). The vaccination status of 73 people could not be ascertained.
These results, released by the Centre December 24, again raised the question of efficacy of vaccines in protecting people. A debate is raging globally on the need for booster shots. While many countries like the United Kingdom and Israel have started providing them, India is yet to decide.
Union health secretary Rajesh Bhushan told reporters that the government will decide based on scientific evidence. India has provided at least one dose of a COVID-19 vaccine to some 90 per cent of the population while some 60 per cent of the population is fully vaccinated.
Scientific evidence, however, remains patchy. A series of peer-reviewed studied accepted for publication in the Nature journal indicate that neutralising antibodies produced by existing vaccines or prior infection by the virus do not work on omicron — the latest variant if concern.
These studies have covered the Oxford-AstraZeneca vaccine — marketed in India as Covishield — but not the indigenous Covaxin.
In one of the studies, researchers investigated vaccines prepared by Pfizer-BioNTech, Moderna Inc, Johnson & Johnson (J&J), and Oxford-AstraZeneca. When sera samples from 54 fully vaccinated people were tested against the virus, it was seen that antibodies in the blood were not very effective. The sera samples included two persons earlier infected by the virus and 15 who received Pfizer-BioNTech and Moderna boosters. Researchers found that participants who had received boosters recorded a smaller decrease in antibody neutralisation.
In another study, researchers from France’s Institut Pasteur tested the efficacy of antibodies in sera from 80 vaccinate individuals, some of whom were earlier infected by the virus while some were not.
The team could not detect any antiviral activity in the sera from recipients of the Pfizer-BioNTech or AstraZeneca vaccines, sampled five months after receiving the second dose. Samples from 20 people who received a third Pfizer-BioNTech dose too showed a six-fold decrease in the ability to neutralise omicron.
Even the sera collected from 40 previously infected individuals collected six or 12 months after symptoms too displayed low or no neutralising activity.
Similarly, researchers in South Africa used plasma samples from 19 people who had received two doses of the Pfizer-BioNTech vaccine. Out of these, six individuals had no previous record of SARS-CoV-2 infection.
The team found that there was a 22-fold reduction in vaccine elicited neutralisation for omicron compared to an older strain of the virus. However, samples from vaccinated people who had earlier contracted the disease continued to neutralise omicron to levels comparable to neutralisation of the older variant in people who were vaccinated but were never infected.
In yet another study, researchers from Switzerland tested the activity of vaccine or infection elicited antibodies against omicron and Wuhan variants. Samples from vaccinated individuals were taken between seven and ten months after the last dose; except those vaccinated with the J&J vaccine.
Plasma from convalescent patients or individuals vaccinated with J&J , Sputnik V or Sinopharm vaccines had little or no neutralising activity against Omicron. Individuals vaccinated with Moderna, Pfizer-BioNTech and AstraZeneca vaccines displayed 33, 44 and 36-fold reductions in neutralisation activity, respectively, against Omicron relative to the Wuhan isolates.
The studies looked at the status of neutralising antibodies and not T-cell regulated immunity. While antibodies are proteins and disappear after a few months, T-cell regulated immunity provides long-term immunity.
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