‘Herd debate’ catches fire in India

October 5, 2020 0 By FM

In India, the conversation on herd immunity intensified in July following sero-surveys in New Delhi and Mumbai, two of India’s most populated metros, that showed extensive COVID-19 infections in both cities. 

Serosurveys are used to measure the presence of antibodies against an infection in a population. 

The first survey in Delhi revealed that 23.48 percent of the city’s population has been exposed to the coronavirus and has developed antibodies. The second sero-survey, in August, saw this number rise to almost 29.1%, while media reports indicate that this has further increased to around 33% in the September survey.

If these findings are correct, it means that millions of people have been infected in these cities so far, which is way above the reported numbers for the country as a whole.

Mumbai’s serosurveillance data found a high degree of COVID-19 infection in slum areas, where nearly 57 percent of the people were already infected by July.

As per a recent simulator modelled report worked out by the Tata Institute of Fundamental Research (TIFR), almost 75 percent people living in Mumbai’s slum areas and 50 percent from non-slum areas will eventually develop antibodies against the novel coronavirus. The projections submitted to the BMC said that herd immunity may develop by December 2020 or January 2021.

“Looking at the projections, it seems that by and large, we will reach herd immunity by January 2021,” said Sandeep Juneja, Professor and Dean at the School of Technology and Computer Science at Tata Institute of Fundamental Research in Mumbai.

This IISc-TIFR simulator is a relative model in which 12.4 million people living in the city are modelled on a computer and seeded with infections and matched with fatalities, he added.

India’s most populous state UP started serosurveillance in the 11 most COVID-19 affected districts during the first week of September.

UP has successfully managed the fatality rate at 1.58%, lower than the national fatality rate of 1.87%, despite a large number of migrants coming back to the state from infection hotspots.

Data from private labs which are conducting antibody tests in Hyderabad and elsewhere have also suggested that the antibodies to fight coronavirus have been developed in nearly 50 percent of tests done by them.

A pilot project by health authorities in 4 districts in Andhra Pradesh showed that more than 16 percent of the population in Ananthapur, nearly 15 percent of those in East Godavari, about 30 percent in Krishna and 8 percent in Nellore district had already generated antibodies and developed community immunity against the virus.

Uneven immunity 

Going by the numbers, experts believe that different parts of the country will get closer to herd immunity at different times.

Herd immunity may be generated in pockets rather than uniformly across the country, experts say.

In addition, since seropositivity tests usually measure the level of antibodies, they do not necessarily mean protective immunity. These antibody responses may be short-lived, leaving those people susceptible to repeat infections.

Current serosurveys do not measure the T cell response, which are more crucial in protecting an individual from another bout of infection by the same pathogen.

Therefore, it would be a mistake to talk of herd immunity on a national scale, as conditions such as population density, virus prevalence and the rate of transmission of infection vary across the country, and even within a state.

Natural immunity not feasible: Minister

A Spanish study published in The Lancet in the first week of July cast doubts over the feasibility of herd immunity as a way of tackling the pandemic.

The study of over 60,000 people estimated that just five percent of the Spanish population has developed antibodies.

Countries that expected to develop herd immunity through a natural process of allowing disease transmission among less risky groups reported very high morbidity and mortality and had to abandon the strategy, pointed out India’s Minister of State for Health Ashwini Kumar Choubey, in a written reply to the upper house of Indian Parliament (Rajya Sabha) recently.

Speculations were rife whether India is going in for the natural herd-immunity strategy as the government initiated a full-fledged reopening of business activities amidst surging case counts.

India began reopening after what is described as one of the longest and toughest virus lockdowns anywhere in the world and at a time the COVID-19 case tally began to touch new highs. The daily case numbers reached one lakh mark in the fourth week of September, making India the world’s second worst-hit country after the US in cumulative numbers.

Huge job losses and the economic downturn that followed the shutdown seems to have forced the country to reopen. India’s economy shrank by an eye-watering 24% in the three months ended June compared with the previous year — in one of the most severe contractions of any nation as a result of the pandemic.

The steady and uncontrolled increase in infections has led many people to speculate that state governments are following a herd immunity strategy to fight the COVID-19 pandemic.

In his response, Choubey said the union health ministry issued plans, procedures, advisories, and SoPs to the state governments for the containment of the pandemic, based on the strategy of breaking and suppressing the chain of transmission. He warned that allowing the virus to run through the population in the absence of robust pharmaceutical and healthcare interventions might have disastrous consequences in terms of morbidity and mortality.