The durability of immunity post the Covid infection persists for about 9 months, Indian Council of Medical Research Director General, Dr Balram Bhargava, said on Thursday.
The whole SARS CoV2 virus infects an individual in natural settings, and elicits three kinds of responses - antibody mediated, cell mediated immunity, and immunological memory, he said.
"Based on several global and Indian scientific researches, if you get an infection, you are generally protected for 9 months," he said at press briefing on the Covid situation.
Immunological memory to SARS CoV2 lasted for 8 months in the natural settings as per a study in the US, published in journal Science. Another study from China says that antibody and cellular immune responses persists more than 9 months after infection, while the longitudinal investigation in the US of multiple studies have shown that antibody responses persists for more than 13 months post infection, he added.
About three studies from India - two by the ICMR and one from Bombay conducted on 284, 755 and 244 patients, respectively, Bhargava said that immunity persists for up to 8 months, 7 months, and 6 months respectively.
"Most of the studies have shown that it persists for 8 to 13 months post infection and we have taken it as around 9 months," he added.
The ICMR chief also said that all Covid vaccines do not prevent infection and are primarily disease modifying.
"All Covid vaccines, whether they are from India, Israel, US, Europe, UK or China, are primarily disease-modifying. They do not prevent infection. The precautionary dose is primarily to mitigate the severity of infection, hospitalisation and death," he said.
Meanwhile, approximately 90 per cent of the adult population in India has been vaccinated against Covid-19 with the first dose, while 63.5 per cent of those eligible have been administered both doses of vaccines, Joint Secretary, Health, Lav Agarwal, said at the briefing.
He said that the weekly positivity rate of more than 10 per cent is being noted in 8 districts - six in Mizoram, one in Arunachal Pradesh, and Kolkata.