A latest study on the epidemiology and transmission dynamics of Covid-19 in Andhra Pradesh and Tamil Nadu has found a high prevalence of infection among children who were contacts of cases around their own age. The study also said not all infected individuals transmitted the disease as a prospective follow-up testing of exposed contacts revealed that 70 per cent of infected individuals did not infect any of their contacts.
Only 8 per cent of the infected individuals accounted for 60 per cent of observed new infections, it added.
The Centre for Disease Dynamics, Economics and Policy, New Delhi, the governments of AP and Tamil Nadu and the University of California at Berkley studied disease transmission patterns in 5,75,071 individuals exposed to 84,965 confirmed cases of COVID-19.
The study, based on data collected by tens of thousands of contact tracers in the states of Andhra Pradesh and Tamil Nadu, was said to be the largest and most comprehensive analysis of COVID-19 epidemiology to date and its findings were published in the latest issue of Science journal.
AP Special Chief Secretary K S Jawahar Reddy is one of the authors of the study report.
Jawahar Reddy said risk of transmission from an index case to a close contact ranged from 2.6 per cent in the community to 9.0 per cent in the household.
“It does not differ significantly with respect to the age of the index case (infected person).
Infection probabilities ranged from 4.7-10.7 per cent for low-risk and high-risk contact types, respectively.Same- age contacts were associated with the greatest infection risk," he said, quoting the study.
This study presented the largest empirical demonstration of super-spreading, he added.
The study found high prevalence of infection among children who were contacts of cases around their own age.
It also revealed that enhanced infection risk among individuals exposed to similar-age cases was also apparent among adults.
However, not all infected individuals transmitted COVID-19.
Referring to coronavirus mortality, the study said case-fatality ratios spanned 0.05 per cent in the 5-17 years age group to 16.6 per cent in the 85-plus years age group.
Men were 62 per cent more likely to die of coronavirus infection than women.
In the two states, 63 per cent of those who died of Covid-19 had at least one comorbidity while 36 per cent had two or more comorbidities.
About 45 per cent of the victims were diabetic, the study noted.
“Unlike observations in high-income settings, deaths in India are concentrated at ages 50-64 years.The CFR is higher in the 40-70 age group in India," the study pointed out.
According to CDDEP Director Ramanan Laxminarayan, their study was made possible by the significant contact tracing effort in Andhra Pradesh and Tamil Nadu, which involved tens of thousands of healthcare workers.
In the two states, as many as 30,84,885 contacts of the confirmed cases of Covid-19 infection were traced by August 1.
The study found that the traced contacts were younger and more often female.
“While our analysis is limited in that it does not necessarily capture all secondary infections (among contacts who were not reported), these observations are consistent with the presence of super-spreading related to differences in individual contact patterns," Laxminarayan noted.