An estimated one in 15 individuals aged 10 years and above were exposed to the novel coronavirus infection by August, indicating that a large part of the population is still susceptible to the virus, according to the second nationwide sero-survey.
Releasing the findings on Tuesday, ICMR Director General Balram Bhargava said 6.6 per cent of the 29,082 people (aged 10 years and above) surveyed from August 17 to September 22 showed evidence of past exposure to Covid-19. The prevalence was higher for adults (aged 18 years and above) at 7.1 per cent.
This is a significant increase from the 0.73 per cent prevalence found in the first sero-survey, conducted between May 11 and June 4, among adults in 70 districts. The second survey was conducted in the same districts, but children (above 10 years) were included.
Significantly, the second survey shows that children are also vulnerable to the infection. “The seroprevalence was not different by age group or gender. All age groups above 10 years were found to have been exposed to the infection. Earlier, we were under the impression that it does not affect below 18 years. But we have found that there is no difference,” said Bhargava.
“The data shows that a large proportion of the population continues to remain susceptible. Prevention fatigue has to be avoided and we have to stick to the 5T strategy: test, track, trace, treat and use of technology. Non-pharmacological interventions like physical distancing and use of face masks continue to remain essential. In light of the upcoming festivities, winter season and mass gathering, containment strategies must be implemented by states most effectively,” Bhargava said.
The survey, which was conducted in the backdrop of restrictions being eased and resumption of economic activity, reveals that the risk gradient is highest in urban slums. The prevalence in urban slums stood at an estimated 15.6 per cent, as compared to 8.6 per cent in non-slum urban areas, and 4.4 per cent in rural areas.
“…the risk gradient is highest in urban slums. Therefore, people-centric and risk-focused interventions have to be done more in the urban slums; and elderly and individuals with comorbidities have to be protected,” Bhargava said.
With testing being ramped up in the last two months, the survey found 26-32 infections per reported case by August, as compared to 81-131 infections per reported case in the first round in May.
“The novel coronavirus infection has much wider dimension. There are asymptomatic infected persons, which is a well-known dimension. But what is notable is that in the last results, we estimated that with one confirmed case, we found 81-131 cases. Now, that number is 26-32. When we have increased testing, it is shown that we are tracking the virus more intensely. But remember, we can never, in an epidemiological sense, identify every asymptomatic individual. That is why sero-survey is an additional tool for contract tracing,” said Dr V K Paul, Member, NITI Aayog.
Dr Paul said the data has to be analysed from two perspectives for implementing future strategies on containment. “The extensive second round was conducted in a systematic way…we have to look at the results from both sides. First, the (containment) measures adopted have kept the prevalence at lower levels, despite the un-lockdown and resumption of economic activity; second, it reveals that more than 90 per cent of the population is susceptible to the virus. And the risk continues,” he said.
“In winter, respiratory viruses spread faster. In the next five months, maintaining social distance and wearing a mask becomes even more important. The data is an indicator that we have to celebrate festivals in small groups,” he said.
Responding to a question, Bhargava said there are two ways of looking at the data. “Currently, we can say that our seroprevalence is comparable to the sero-surveys across the world; whether you look at Switzerland (8 per cent), United Kingdom (7 per cent), Belgium (5 per cent), US (9.3 per cent),” he said.
“The sero-survey gives us the data on exposure to the virus; whether the individual has developed a disease or not, that data is not there. Second, this is the data collected statistically from different districts, and we extrapolate the data and try to get a percentage… the first tool is to test, the second tool is to look at the sero-survey, and the third tool is to look at sewage water to find the prevalence. These are epidemiological tools that guide us,” he said.
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