New Delhi [India], December 3 (ANI): A large section of India's population has "hybrid immunity" against COVID-19 and the "strong" resistance it entails is a positive factor in view of emergence of Omicron variant of the virus, a senior scientist has said.

Dr Anurag Agrawal, Senior Scientist and Director of the CSIR-Institute of Genomics and Integrative Biology, New Delhi, said people with best immunity at present are those with "hybrid immunity".

"Right now people with best immunity are those with hybrid immunity, which is the largest proportion of the country's population. Even one dose of COVID-19 vaccine gives you good immunity if you have previously had an infection," Dr Agrawal told ANI.

He said there are three types of immunity - natural immunity coming from infection, vaccine immunity coming from vaccines and hybrid immunity, in which a person who has previously been infected also gets vaccinated.

"India has all three types of people. A large number of people have been infected, we know that from the ICMR serosurvey. Our big vaccine push was after the second wave, and therefore, these people were infected before they got the vaccine. Hybrid immunity is the strongest of all immunities," he said.

Talking about people who got fully vaccinated before the second wave arrived in India in April this year, Dr Agrawal, said that their immunity would have declined over time and special focus is needed for boosting their immunity with measures such as booster dose.

"The worst immunity is in people who have not yet been vaccinated. We must take care of very important section of the population like healthcare workers who got double vaccinated before the second wave and have not got infected. They might become susceptible again and we must provide an appropriate way of protection like a booster (dose). And that is something for us to consider as we meet other priorities," he said.

Two samples in Karnataka have shown Omicron strain, the first cases of the new variant in India. One of the persons whose sample showed the strain has returned to South Africa after he tested negative in a subsequent RT-PCR test. The first case of strain was reported from South Africa.

Union Health Minister Manuskh Mandaviya said on Friday that RT-PCR tests have been done of 16,000 passangers from 'at risk' countries and 18 samples have been sent for genome sequencing to determine if they have Omicron variant of the virus or not.

The minister said there are 373 cases of Omicron - classified as variant of concern by WHO - in 29 countries. India is conducting RT-PCR tests of passengers from "at risk" countries and revised guidelines have been issued for travel from these countries. (ANI)