The second survey found dramatically different seroprevalence of COVID-19 in urban slums, non-slums areas and rural areas than the first.
The Indian Council of Medical Research (ICMR) has found in its second nationwide sero survey for antibodies against SARS-CoV-2, that over seven percent of India’s adult population seems to have been exposed to the coronavirus before the end of August. The survey was done between 17 August and 22 September, and its results were shared by the Union Health Ministry on Tuesday. This is a fair jump from the 0.73 percent exposure recorded in the first survey – conducted in the same 700 villages and urban wards as the second serosurvey.
Blood samples from 29,082 people were tested to look for IgG antibodies, which indicates exposure to the novel coronavirus at the population level. The sero survey is part of a larger effort to understand how widespread the prevalence of COVID-19 is in the Indian population.
Key findings from the second sero survey
–A considerable section of the Indian population has not yet been exposed to the virus and remains at varying degree of COVID-19 infection risk, depending on where they live
–One in 15 people (10 years of age or older) is likely to have been exposed to the coronavirus (SARS-CoV-2) by end of August.
–The risk of infection was twice as high in slums (15.6 percent seroprevalence) as non-slum areas (8.2 percent seroprevalence) in urban centres, and four times higher than in rural areas (4.4 percent seroprevalence).
–The seropositivity in various strata of society were dramatically different from what the first survey reported. The first survey found a much higher seropositivity in rural areas (69.4 percent) compared to urban slums (15.9 percent) or non-slums (14.6 percent). That said, the findings from the first survey are somewhat compromised, since only a quarter (25.9 percent) of the clusters surveyed were located in urban areas.
–There was lower infection-to-case ratio in August compare to May – a reflection of a substantial increase in testing and detection across the country, the ministry said.
–For every confirmed COVID-19 case in August there were 26 to 32 infections that went undetected. In May, the same figure was 81-130 undetected for every case diagnosed – a success that the government claims is due to better contact tracing and tracking for COVID-19.
States with the highest seroprevalence
Mumbai showed the highest seroprevalence of any city in India, with 57.8 percent of samples (from slums) positive for SARS-CoV-2 antibodies. This figure dropped to 17.4 percent for samples from non-slum areas.
Delhi recorded a 29.1 percent seroprevalence in the second round of sampling that was conducted between 1-7 August. This was higher than the 23.1 percent recorded in the first round conducted between 27 June and 10 July.
Puducherry was next with a seroprevalence of 22.7 percent in the second sero survey (10-16 September). The Union Territory has recorded some 27,000 confirmed cases, 515 are deaths and 5,014 active cases till date. Puducherry’s seroprevalence has seen a rapid rise from only 4.9 percent in the first round of survey (11-16 August).
Chennai, Ahmedabad, Indore
Chennai recorded a seroprevalence of 21.5 percent and Ahmedabad 17.6 percent, with Indore in Madhya Pradesh registering 7.8 percent. Each of these figures correspond to two different sero surveys that were conducted independently of each other.
The ministry warned that with the holiday season around the corner and the many festivals that will be celebrated, mass gatherings need to be strictly avoided. State governments need to come up with “inventive containment strategies” for this, said the central government.
The sero survey also highlighted the need for the public to practise ‘non-pharmacological interventions’ – social distancing, correct cough etiquette, use of face masks and hand sanitizers – to limit the spread of COVID-19.
Elderly people, individuals with co-morbidities, children and pregnant women remain susceptible to infection and still need to take extra precautions wherever possible, the government stressed.
India has a cumulative tally of 61.45 lakh confirmed COVID-19 cases and 9.4 lakh active cases as of 30 September. 70,589 new cases were reported in the past 24 hours, as per government data released this morning, and 776 people died.
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