'Too many variables in herd immunity, vaccine only option'

New Delhi: Six months into the pandemic, while the debate over whether India has attained herd immunity or is on its way to doing so rages on, doctors and experts have pointed to multiple serosurveys and other studies showing around 20 per cent exposure to the virus to conclude that it is not realistic to hope for herd immunity.

When a majority of a population attains immunity against a disease, the population is said to have attained her immunity as the immune members of the population will automatically stop the virus from spreading, leaving only so many that can be infected.

There are two types of herd immunity, according to Dr Deeksha Mittal, Clinical Scientist at the Department of Nephrology at All India Institute Of Medical Sciences (AIIMS).

"The first kind of herd immunity is through a vaccine," she said, adding that the second is the natural way, where you let enough people get infected so they can develop antibodies and attain immunity. However, there is not nearly enough insight into COVID-19 antibodies to make reasonable conclusions about attaining herd immunity this way.

Dr Rahul Nagpal, Director and HOD (Paediatrics & Neonatology), at Fortis Flt. Lt. Rajan Dhall Hospital said that it is difficult to conclude whether Delhi has entered herd immunity or not.

Dr Nagpal added that it is assumed that 20 per cent of people have been infected by the virus, which is not enough to cause herd immunity. He said that at least 50 to 60 per cent of the population needs to be infected to kick off herd immunity.

Dr Mittal, however, believes that the population is on its way to herd immunity and that it largely depends on the R-value of the virus — which estimates how many people one infected person can pass it on to. Currently, Delhi's R-value is at 0.66 per cent, which means each infected person is passing it on to less than one person.

However, both Dr Mittal and Dr Nagpal agree that a vaccine is the only solution.