In two states in India, Tamil Nadu and Andhra Pradesh, COVID-19 cases and deaths have been more heavily concentrated in younger cohorts than is seen in high-income countries, among other trends.
These results, from a study based on surveillance and contact tracing data, offer a window into the pandemic's trajectory in a low- and middle-income country, where most COVID-19 cases have occurred, and from which insights to guide control measures are urgently needed.
While multiple modeling studies have attempted to assess how COVID-19 might affect people and communities in low-and middle-income countries, almost no primary studies of disease dynamics and clinical outcomes of COVID-19 are available from these locations, to validate models and inform intervention strategies.
The populations of Andhra Pradesh and Tamil Nadu - states with among the largest healthcare workforces in India - account for approximately 10% of the country's total population. Both states began rigorous disease surveillance and contact tracing early in response to the pandemic. Ramanan Laxminarayan and colleagues analyzed surveillance and contract tracing data from these two states' programs.
Epidemiological data and laboratory test results were available from 575,071 tested contacts of 84,965 confirmed cases. Analyzing these and other data, the authors report that cases and deaths in the two Indian states were concentrated in younger cohorts than expected from observations in higher-income countries, findings that "may indicate the identification of less-severe infections through active case-finding," the authors say.
Same-age contacts were associated with the greatest infection risk, a pattern strongest among children ages 0-14 years and among adults older than 65 years. Case-fatality ratios spanned 0.05% at ages 5-17 years to 16.6% at ages exceeding 85.
The authors note that estimates of time-to-death in both states is rapid compared to what has been observed internationally (for example 13 days to death from the date of hospital admission in the U.S., compared to succumbing to death within six days in the two Indian states, for about half of the cases ascertained in this study).
The most prevalent conditions among those who died were diabetes, sustained hypertension, coronary artery disease, and renal disease, with at least one comorbid condition noted among 62.5% of fatalities, in comparison to 22% of fatalities in the United States as of 30 May, 2020.
In the two Indian states, only 17.9% of COVID-19 deaths occurring on or before 1 August, 2020 were among people older than 75, compared with 58.1% of COVID-19 deaths in the United States.
While the role of children in transmission has been debated. We identify high prevalence of infection among children who were contacts of cases around their own age."
The authors note several implications and limitations of their study. They conclude: "Similar studies are necessary to inform the successful adaption of epidemic control measures in low-resource settings globally."