The patterns of infections and deaths caused by SARS-CoV-2 differ between resource-poor settings and richer places, according to a massive contact-tracing study that used data from two Indian states1.
Researchers at University of California, Berkeley analysed data from almost 85,000 people with COVID-19 and 600,000 of their close contacts in Tamil Nadu and Andhra Pradesh and compared this with data from US cities.
The data revealed that as the age increased above 40 years, in the Indian states the incidence of COVID-19 declined steadily. In contrast, the disease incidence climbed steadily as age increased above 65 years in the United States.
Mortality rates for those aged 75 and above were markedly lower in India than in the United States. The researchers say this may be because of the stringent stay-at-home orders for older Indian adults, or because people in India who live to old age tend to be relatively wealthier compared with those who die younger.
The study also found that people were most likely to infect others within their own age group, especially children, suggesting that socialising among them could contribute to viral spread.
The researchers observe that primary data are urgently needed from low-resource countries to design better control measures.
1. Laxminarayan, R. et al. Epidemiology and transmission dynamics of COVID-19 in two Indian states. Science (2020) doi: 10.1126/science.abd7672