Derivatives of the Covid-19 Delta variant have the potential to reduce the neutralisation ability of the Covishield vaccine, especially among those who have never been infected with the virus, said ICMR researchers calling for booster doses.
They, however, added that even with reduced neutralisation ability, Covishield will protect against severe disease and fatalities.
“Delta variant has slowly dominated other variants of concern. Subsequently, Delta has further mutated to Delta AY.1 to Delta AY.126. Of these, Delta AY.1 has been reported from several countries, including India. It’s considered highly infectious and probable escape mutant,” researchers said in the latest study posted on bioRxiv (a repository of pre-print studies).
An escape mutant is one that can escape human immune response or vaccine-induced immune response. Researchers had previously evaluated the efficacy of Covaxin against Delta AY.1 (because it is an escape mutant) and found the vaccine to be effective.
The study is yet to be peer-reviewed. Researchers evaluated the neutralising potential of blood samples from people who had received two doses of the Covishield vaccine.
They studied three types of blood samples. The first was from people who have been fully vaccinated with Covishield and have never been infected with Covid. The second was from people who have been fully vaccinated after recovering from Covid infection in the past. The third was from people who got infected with Covid after being fully vaccinated, that is people
who suffered breakthrough infections.
They observed the highest reduction in the level of neutralising antibodies against the Delta — a reduction of 27.3-fold — among fully vaccinated individuals who had never been infected with Covid, compared to other groups and variants.
Neutralisation was reduced against Delta and AY.1 in all three groups.
However, the team said vaccines will continue to provide sufficient protection against the severity of the disease and fatality, based on breakthrough infections data they analysed.
“Several studies have reported the increase in immune response in Covid-19 recovered cases and breakthrough infections post-vaccination,” the team noted in the study.
They said that such a rise in immune response actually helps effectively neutralise the immune escape variants in breakthrough Covid cases.
“Once the individual gets re-infection after vaccination or vaccination post-recovery, memory B cells (a type of white blood cells involved in immune response) are triggered that generate higher levels of immune response,” the team noted.
They added that a booster dose vaccination among fully vaccinated people who have never been infected with Covid-19 would achieve a protective immune response to fight against emerging SARS-CoV-2 variants.