Waning Effect Of Covid-19 Antibodies Makes Case For Booster Shots
NEW DELHI :
The effect of covid-19 vaccine Covishield starts waning after six months of vaccination, a research study found, making a case for booster doses to protect from the viral pandemic.
According to the study conducted by Pune’s ICMR-National Institute of Virology (NIV), neutralizing antibodies, which are generated by the body after infection or vaccination and guard against future infection, become less effective after this period. The study, funded by the Indian Council of Medical Research (ICMR), was conducted in February and March, and published in the latest issue of Journal of Infection.
The NIV researchers collected blood samples from three groups of individuals. The first group of 24 so-called ‘covid-19 naïve’ individuals had neither contracted the virus before nor been vaccinated against it; the second group of 17 had recovered from covid-19 and had then received two doses of Covishield; and the third group of 46 had contracted covid-19 after receiving two doses of Covishield, in what is called breakthrough infections.
“The neutralizing antibodies (NAb) titres were lowest for Omicron with serum samples of covid-19 naïve vaccinated individuals than the recovered cases and breakthrough cases. The study suggests the Omicron variant significantly evades immune response generated with vaccine-elicited neutralizing antibodies after six months of two doses of Covishield covid-19 vaccine,” said Dr Pragya Yadav, senior scientist and chief author of the study.
An email sent to Serum Institute of India Ltd, which manufactures Covishield under licence from AstraZeneca and Oxford University, remained answered till the press time.
The highly transmissible SARS-CoV-2 Omicron variant has also caused an exponential rise in covid cases, with breakthrough infections and re-infection worldwide, including India.
“Further, in the study, we found that all 17 recovered cases were infected with the Delta variant, while four with the Kappa variant. Of the 46 breakthrough cases, the complete genome could be retrieved only from 21 cases based on the viral load. All the three groups effectively neutralized the B.1, Beta and Delta variants than Omicron. This demonstrates the need of booster dose of mRNA vaccine to boost the immune response to protect against Omicron,” Dr Yadav said over the phone.
The Omicron variant has evolved into 55 sub-lineages detected in 164 countries. Among them, BA.1.1 and BA.2 have been found to be dominating. Recently, the World Health Organization also warned about the XE variant, which is a mutant hybrid of BA.1 and BA.2.
“Even though the highest fold-reduction among breakthrough cases was observed with Omicron variant, it also had highest NAb titre than the recovered and vaccinated individuals. Breakthrough cases also represented maximum neutralizing antibody response against all the variants other than vaccines and recovered cases,” she said.
Omicron, first reported in South Africa in November, is now the dominant strain of covid-19 globally, and the most transmissible variant till date.
India started its mammoth covid-19 vaccination drive in January last year. At present, all adults are eligible for the vaccine, besides children aged 12-14. As of date, India has detected more than 43 million cases, with 522,116 deaths. Under a nationwide drive, more than 1.87 billion vaccine doses have been administered so far.