Covishield recipients with no history of Covid have shown the least neutralizing power against Omicron’s BA.1 variant, a study conducted by the ICMR-National Institute of Virology (ICMR-NIV) have found, indicating need for booster shots.
“With the highest mutations in the spike region, Omicron also showed better immune escape in breakthrough cases that involved Delta than other variants. Breakthrough cases jabbed with Covishield, however, had highest neutralizing antibodies against all variants studied, than recovered and Covid-naïve vaccinated individuals,” an ICMR scientist told The Times of India.
To conduct the research, serum samples were collected from 24 Covidnaïve individuals 180 days after they were administered with the second dose of Covishield and from 17 people who had earlier recovered from Covid and vaccinated with two doses of Covishield. In the third group, 46 people who got SARS-CoV-2 breakthrough infection after two doses of Covishield were included
The serum samples of third group were collected 14-30 days after their infection and out of the 46 breakthrough cases, complete genome could be retrieved of only 21 cases, the TOI reported.
Earlier, the NIV had found out that neutralising antibody levels waned after six months in those who were fully vaccinated against the coronavirus with Covishield, Covaxin and a mix of both — Covishield as the first dose and Covaxin as the second dose with regard to Omicron variant.
The heterologous vaccination regimen of administering the first dose of Covishield, followed by the second dose of Covaxin, however, had given a very good neutralising response against Delta and other Variants of Concern, Dr Pragya Yadav, a scientist at the NIV, said.
The study findings were published in the Journal of Travel Medicine recently. The study involved three cohorts — a heterologous group with 18 individuals who were inadvertently administered the first dose of Covishield and the second dose of Covaxin in Uttar Pradesh and the other two groups comprising 40 individuals each receiving two doses of homologous Covishield or Covaxin.
For the Covishield study, scientists later assessed the neutralization potential of these serum samples against B.1, Delta, Beta and Omicron variants. “All the three groups neutralized B.1, Beta and Delta variants more effectively than Omicron. Geometric average concentrations of neutralizing antibodies in the serum of Covid-naïve group were found to be lowest against Omicron — at 0.11. This average in the recovered cases was 11.28 and 26.25 in case of breakthrough cases,” the ICMR scientist said.
Besides, since Omicron’s BA.1 showed significant immunity escape, BA.2 and the currently emerging subvariants under Omicron BA.2 can also be expected to show similar abilities, he added.
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