PUNE, Apr 24
A study of vaccine effectiveness against SARS-CoV-2 variants has found that Covishield recipients with no history of Covid had the lowest levels of neutralizing activity against Omicron’s BA.1 sub-lineage, when compared to recovered patients and breakthrough cases given two doses.
A similar study had earlier found that Covaxin too offers limited protection against Omicron, which due to mutations, has acquired immune-escape abilities. Experts from the ICMR-National Institute of Virology (ICMR-NIV), who conducted both the Covaxin and Covishield investigations, said the studies indicate people should get booster shots as soon as they’re eligible.
The Covishield study found that blood serum from 'Covid-naïve' but vaccinated individuals had the least mean concentration of neutralizing antibodies against Omicron, compared to serum from recovered patients or who had experienced breakthrough infections (a Covid bout despite two jabs of Covishield)
An ICMR scientist said, “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.”
Serum samples were collected from 24 Covidnaïve individuals 180 days after the second dose of Covishield and from 17 people who had earlier recovered from Covid and vaccinated with two doses of Covishield. The third group had 46 people who got SARS-CoV-2 breakthrough infection after two doses of Covishield.
Serum samples of this group were collected 14-30 days after the infection. Of the 46 breakthrough cases, complete genome could be retrieved of only 21 cases. Seventeen cases in this breakthrough group had contracted the Delta variant of SARS-CoV-2, while four had the Kappa variant.
Researchers 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. The scientist added that 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.
Omicron was first detected in South Africa in November last year. ICMR-NIV scientists Dr Pragya D Yadav, Dr Gajanan N Sapkal, Dr Rima R Sahay and others were involved in the study, which has been accepted for publication in Journal of Infection. TNN