An international team of researchers published a detailed study Wednesday of COVID-19 transmission patterns in low-resource settings after studying two states in India.

The researchers analyzed data from more than 575,000 individuals in the states of Andhra Pradesh and Tamil Nadu using contact tracing. Study co-author and UC Berkeley School of Public Health assistant professor Joseph Lewnard noted that this study was unique as it was the first large-scale study conducted in low-resource areas rather than in high-resource ones.

According to Lewnard, 71% of the 85,000 individuals who tested positive for COVID-19 in the study did not transmit the virus to their contacts. This phenomenon, known in epidemiology as superspreading, occurs when a mass transmission of a virus can be attributed to only a select few individuals.

“Most people who get infected don’t seem to pass the virus on to anyone else or to many other people,” said John Swartzberg, clinical professor emeritus of the UC Berkeley School of Public Health. “It appears that the virus is not evenly distributed in terms of how it spreads.”

The results of the study suggest that transmission rates can differ based on geography, socioeconomic conditions, age and other environmental factors, according to School of Public Health professor Lee Riley.

The researchers also observed that children play a substantial role in the transmission of COVID-19. According to Ramanan Laxminarayan, study co-author and director of the Center for Disease Dynamics, Economics and Policy, children transmit the virus at the same rate as adults do, and they mostly transmit to other children.

Lewnard noted that this was the first study with conclusive evidence about the risk of COVID-19 transmission and infection among younger age groups.

“We see high rates of infection among contacts whose exposures were to children, and that is certainly contrary to what has been assumed by some people up to this point,” Lewnard said.

Another significant finding was that people who tested positive in different age groups in India and the United States have different mortality rates. According to Laxminarayan, people between the ages of 40 and 70 in Andhra Pradesh and Tamil Nadu are more likely to die from COVID-19 than people of the same age range in the United States. However, people over the age of 85 studied in these two Indian states are less likely to die due to COVID-19 than Americans of the same age range.

Laxminarayan called this a “survivorship bias,” adding that most people in India who live to an old age were probably healthy to begin with. The study suggests that those who live past India’s average life expectancy of 69 years tend to have higher socioeconomic status.

Riley noted that, due to the strong public health systems and contact tracing capabilities in Andhra Pradesh and Tamil Nadu, mortality rates of each age group may differ greatly from other Indian states.

Swartzberg related these socioeconomic factors to low-income communities in the United States, which have experienced a “disproportionate” number of cases and deaths.

“It’s always the people from the lower socioeconomic strata that suffer the most and die the most,” Swartzberg said. “That’s no exception.”