India is nowhere close to herd immunity, countrywide serosurvey shows

The second round of serosurvey conducted by the Indian Council of Medical Research (ICMR) has revealed that only 6.6 per cent of the country’s population has so far been exposed to the novel coronavirus or SARS-CoV-2.

The results of the second countrywide serosurvey showed that India was very far from herd immunity and a large section of its population still remains susceptible to the virus, ICMR Director-General Balram Bhargava said in a press conference September 29, 2020.

A serosurvey studies what proportion of the population is estimated to have been infected and thus helps in understanding the prevalence of antibodies, also known as ‘seropositivity’ or ‘seroprevalence’. 

The second serosurvey showed one in every 15 individuals in India were estimated to be infected with SARS-CoV-2. The survey was conducted among 29,082 individuals from 700 villages and / or wards from 70 districts in 21 states. The exercise was done from August 17-September 22.

These were the same districts on which the first round of serosurvey was conducted by the ICMR from May 11-June 4. The seroprevalence was only 0.73 per cent at that time.

However, there is one significant difference: Last time, adults aged 18 years and above were part of the survey. This time, individuals below 18 years and above 10 years were also included. “We realised the virus was also infecting this population. Hence, they were included,” Bhargava said.

The overall seroprevalence was found to be 6.6 per cent. But the rate for the exclusive sample of adults aged 18 years and above, was 7.1 per cent. 

There was no difference in rates as far as genders and age groups were concerned, the survey said.

The seropositivity in urban slums was found to be the highest. They showed the seroprevalence of 15.6 per cent, followed by non-slum (8.2 per cent) and rural areas (4.4 per cent).

The risk in urban slums thus was twice that in non-slum areas and four times than the risk in rural settings, Bhargava said.

Earlier, serosurveys conducted in Mumbai and Pune also said urban slums were the worst affected due to congested settings.

“The findings of this exercise clearly show that it would not be right to drop guards on measures such as using masks and maintaining social distance since a large population has yet not been exposed to the virus,” Bharagava said.

The survey showed that for every reported case of the novel coronavirus disease (COVID-19) infection, there were an estimated 26-32 infections that could not be identified. This corresponding range in the first survey was 81-130. “This means we are now testing much more,” Bhargava claimed.

He was asked if this also meant that India had missed such a huge number of cases and they had remained out of the testing net.

“Not a single country has been able to detect all symptomatic and asymptomatic cases. And most serosurveys show a much higher estimated number of infections as compared to those found positive in tests. Therefore, such an interpretation would be wrong,” Bhargava said.

Besides ICMR, many states and municipal corporations have also been conducting their own serosurveys. In Delhi, this exercise has been done twice; the last being in August. The seropositivity was found to be 29.1 per cent. Ahmedabad and Chennai conducted surveys in July and found the rate to be 17.6 per cent and 21.5 per cent respectively. 

Puducherry’s last serostudy conducted in September said as much as 22.7 per cent of its population had been exposed to the virus. In Indore, the exercise was conducted in May and found the rate to be 7.8 per cent. The exercise in three wards of Mumbai said seroprevalence was 57.4 per in slum areas and 17.4 in non-slum areas.

Union health and family welfare secretary Rajesh Bhushan seconded Bhargava by saying that India, on an average, was now conducting 10 lakh tests per day.

“The fact that we are sharing seven-day average testing numbers with you (the press) reveals that we are transparent with our data,” Bhushan claimed. However, there was still no word from either the ministry or ICMR as to how many of the total tests were rapid antigen and RT-PCRs.

It was concerning that several states were not still not following up a rapid antigen test negative case with an RT-PCR test despite the individual being symptomatic, which is mandatory, Bhushan said. 

He was asked as to what the average number of contacts traced for confirmed cases was. In the earlier days of the pandemic, health officials would reveal the number of contacts being traced for confirmed cases in press briefings. “Look at the state bulletins to collect this information,” Bhushan said.

Vinod Paul, the member for health in Niti Ayog, said the upcoming winter season and festivals could heighten the COVID-19 challenge. Respiratory infections witnessed a spurt in winter in any case. If large gatherings during festivals were not avoided, the number of cases could rise exponentially. 

Bhushan said only Kerala and Odisha were registering a spike on a week-on-week basis among the top ten states having maximum number of daily cases. “We do not know the exact reason but we are engaging with these state governments,” Bhushan said.

The other states that have shown initial signs of a downward trend include Maharashtra, Karnataka, Andhra Pradesh, Chhattisgarh, Assam and Telangana. “However, these are only initial signs and we should not jump to conclusions. We have to see if these trends continue,” Bhushan said.