Researchers led by Ramanan Laxminarayan, director of the Washington-based Center for Disease Dynamics, Economics and Policy, gained access to the full set of contact tracing data for the states of Tamil Nadu and Andhra Pradesh from the beginning of the pandemic to on August 1st. In all, the two states had seen more than 435,000 cases as of Aug. 1 and contacted more than three million known exposed contacts. However, as in the rest of the country, the information was incomplete for the majority of cases and contacts. The researchers had complete epidemiological information and laboratory results for 575,071 tested contacts out of 84,965 confirmed cases. Published in the journal Science on September 30, the study offers five key new insights into how the pandemic is unfolding in India.
1. Overpropagation defines disease
The researchers found that positive cases among the contacts were concentrated among a minority of cases. More than 70% of the index cases (“original” or primary cases found by testing) did not infect more people, while less than 10% of the index cases were responsible for almost 60% of the additional infections.
Overpropagation as an event is a common mistake, Laxminarayan said. “Superspreading refers to the fact that a certain proportion of people transmit much more than other people. It does not require an event. “
The study confirms other literature so far on over-propagation, said Gagandeep Kang, one of India’s leading viral infectious disease scientists. “Over-spread is not about the virus, but about the circumstances a person is in,” Kang said. “It could be that the person is in an earlier stage of their illness and therefore is spreading more virus, it could be that they are a person who indulges in a greater social mix, or someone who has a greater opportunity to meet a large number of people, whom it then infects. “
The Tamil Nadu government has been using this information from its data to focus on isolating positive cases within the first 24 to 48 hours of their discovery, said B Chandra Mohan, an IAS official in the state and a member of the monitoring committee. state epidemics. “From our data, we realized very early that if we could identify and isolate all cases within the first 24 hours, we could reduce transmission by 70%,” said Mohan, a co-author of the paper.
2. Long-term shared transportation carries the greatest risk
The study classifies contacts as high and low risk. Those who shared a household with the index case, had contact within one meter of distance without protective equipment, and traveled in the same mode of shared transport within the three rows of the index case were classified as high-risk contacts. More than 10% of those index case contacts tested positive, meaning they had a one in ten chance of being infected. On the other hand, people who shared the same space with an index case without meeting these high-risk contact criteria were categorized as low-risk. Less than 5% of them tested positive.
By far the most risky interaction was being in close proximity to an index case on rideshare for six hours or more – nearly eight out of ten contacts in such cases tested positive. From a political perspective, it would be important to know whether wearing masks could reduce risk in carpooling, Kang said, but this data was not yet available. Living in a shared home carried the next highest risk. But the risk of infection was much lower than in the case of fellow travelers. Less than 10% of contacts in shared homes tested positive, the study showed.
3. The underestimated role of children in transmission
The age group most likely to cause the spread of infections is 20 to 44 years old, the study found. Children also play an important role in the spread of infections, the study shows.
“We found that children are transmitted to each other and to the elderly,” Laxminarayan said. This finding is particularly concerning, as most infections in children are mild and likely to go undiagnosed.
“This is consistent with what we know about influenza, where children are among the main drivers of infections; It shouldn’t surprise us to see this in a respiratory infection, “Kang said.
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The study also found that the risk of transmission was higher among pairs of contacts of the same age. This was particularly true among children. Of all pairs of the same age, the probability of transmission was one of the highest among pairs of children under 14 years of age.
While this could have immediate implications for school closures, Kang recommended viewing the finding in the context of how most Indian schools operate. “Most schools are much better ventilated than other group spaces, and now, in the colder months, you might consider taking classes outside,” he said.
4. The elderly in India have surprisingly low mortality rates
The two states’ covid cases were younger than expected, even taking into account the lower median age in India compared to Western countries, the study found. The incidence of cases peaks in the 40-49 age group in the US and then declines, only to rise again for the elderly, while in Tamil Nadu and Andhra Pradesh, the incidence peaks. maximum at an earlier age and then continuously decreases.
While mortality was higher, as expected, among the older age groups in the two states, it stabilized around age 75, and there was no higher risk of mortality among older people, unlike in the US. This was unexpected, experts said.
This could be due to a “survival effect,” Kang said, in which people who reach very old age are those with relatively better health and no comorbidities. As a result, they could have a lower covid mortality than expected.
5. Deaths happen with worrying speed
In half of the death cases in which the person tested positive before they died, only six days or less elapsed between the test and the person’s death. The median time to death in the two states was much lower than in the US, where it was 13 days from the date of admission to the hospital. In China, the same number ranged from two to eight weeks from the onset of symptoms, according to estimates by the World Health Organization.
The short time to death is an important finding that highlights the lack of access to care in India, Kang said. “We tend to wait too long for care, and we’ve seen it before in other diseases. In the field of diarrheal diseases, where most of my work has been, we see that children arriving in government hospitals appear to have waited much longer for care than in private hospitals, which could mean that poorer people face greater difficulties in accessing early care. ,” she said.
Rukmini S. is a journalist from Chennai.
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