Fresh concerns

Fresh concerns

Neutralising antibodies against Delta variant weren’t found in 16% of those who received both shots of Covishield.

A new study brings home a worrisome aspect about the Covishield vaccine. The Indian Council of Medical Research (ICMR) says that 16 per cent of those who received both doses of the vaccine did not have neutralising antibodies against the Delta variant of Coronavirus. These antibodies were not present in the serum samples of 58.1 per cent of those who took the first dose. It is little consolation that experts argue that saying that the antibodies are not observed is not the same as saying they are not present or that even a low presence of them can provide protection against infection. Over 304 million Indians have so far received Covishield, of whom around 50 million have got both doses. How many of them have low or negligible neutralising antibodies and what should they do to face a future wave of the pandemic? The Government has to come out with a clarification before concern on the subject grows. The study is not peer reviewed and it is also not known which lot of the vaccinated section was tested. The initial set got its second dose within six and eight weeks. After May 13, the second jab is given after 12 to 16 weeks. Students who need to go abroad for education are allowed to take the second dose within 28 days. It is quite possible that those among the fully vaccinated with co-morbidities and the old could have lower neutralising antibodies.

Neutralising antibodies defend cells from virus infection. Of the antibodies produced by the immune response, only a small number is capable of blocking the virus from attacking more cells. This is called neutralisation and the bodies that make it possible are called neutralising antibodies. They usually develop in response to either infection or vaccination and thereafter bind themselves to the virus to block further infection. A vaccine’s effectiveness is measured, therefore, by the quantum of neutralising antibodies present. There are antibody tests which detect antibodies but the neutralising antibody tests alone can help measure the quantity of these antibodies and study how long the immunity can last. The tests can also measure monoclonal antibodies that neutralise the spike protein of the Coronavirus as also neutralising antibody titres — they specifically target the virus and kill it — that act as markers for assessing immunogenicity of people. The ICMR study found that the titres generated by Covishield were lower against the Delta variant of the virus. For 18 months, India has conducted antibody tests and yet this is for the first time the aspect of neutralising antibodies and impact of their presence is gaining currency. Should the Government choose to act on the ICMR report, would there be a nationwide drive to conduct neutralising antibody tests on people who received both doses of Covishield? The level of their presence will determine how to increase protective immunity among the fully vaccinated — with a third dose of Covishield or a single dose of another vaccine or a booster dose.