The first ever large scale study using contact tracing data from two states in India provides critical new information about the virus that causes Covid-19 and how it spreads. Using data from over 85,000 confirmed Covid-19 cases and their 575,071 contacts, the study found that the virus spreads most often among people in the same age group and can cause illness and death even among young people. While previous studies have looked at how the virus spreads in nursing homes and in prisons, this is the first time that we have information about how it spreads among the general population. India and the United States are different settings, however, it is likely that there is a great deal of similarity in how the virus spreads within the two countries.  

The two states of Andhra Pradesh and Tamil Nadu in India implemented robust contact tracing systems in response to the pandemic. Strong contact tracing systems can be used to both decrease the spread of the virus and to provide valuable information about how it spreads. This information is crucial to inform evidence-based policy choices such as whether and how to safely open schools and to what extent businesses should be open.

To identify positive cases of Covid-19, these two Indian states test anyone seeking medical care for severe acute respiratory illness or for flu like symptoms. After a person tests positive for Covid-19 vis reverse-transcriptase polymerase chain reaction (RT-PCR), healthcare workers follow-up with their contacts everyday and test them five to fourteen days after contact with the index case, regardless of whether they have symptoms.

Using this data from the two states in India on index cases and their contacts, researchers found that on average, traced contacts were 1.3 years younger than the index case and more likely to be female. The probability of an index case transmitting the virus to a contact ranged from 4.7 percent in low risk encounters to 10.7 percent in high risk encounters, defined as close social contact or physical contact without any protective measures. The study also found that only 17.9 percent of deaths due to Covid-19 in the two states in India occurred in those ages 75 and above. In comparison, in the US 58.1 percent of deaths occurred in individuals 75 years and above.

For the first time, we have conclusive evidence that the virus spreads most often among people in the same age range. There is no age group that is protected against getting infected by or being able to transmit the virus. Children spread the virus to other children, university students spread the virus to other university students, and working age adults spread the virus to other working age adults. This finding was especially strong in children ages zero to fourteen and in adults over the age of sixty-five. Children age zero to four infected twenty six percent of other children in that age group with whom they had contact. Similarly, children between the ages of five and seventeen infected eleven percent of their peers with whom they had contact. While the spread of the virus occurs most often within the same age groups, it is also possible for the virus to spread from younger people to older adults. Children age five to seventeen infected six percent of adults ages sixty-five to seventy-four with whom they had contact.   

While there is often an assumption that Covid-19 cases among children and young adults will be asymptomatic or mild, that is not necessarily true. Asthma,  obesity, type II diabetes, and genetic susceptibility can all increase a person’s risk for severe Covid-19 illness. These conditions are found in all age groups of the population. Estimates suggest that up to thirty percent of Americans have underlying conditions that put them at higher risk for severe Covid-19 illness. This has important implications for the reopening policies of elementary schools, high schools, and universities and for whether parents will choose to send their children to in person school, if that option is available.

In places where in person learning is taking place, the decision about whether to send children back to school is mostly up to parents. In person learning can cause a spike in Covid-19 cases. Just two weeks after opening, a single high school in Utah saw 90 cases of Covid-19. So how should parents choose whether to send their children back to school in person? To do this, families can start by considering three things: transmission in the area, the risk profile of your child and your family, and what kind of protective measures are being put in place.

Although making decisions regarding keeping our families safe in the context of Covid-19 is new, we make decisions about keeping our families safe everyday. Thinking about the weather as an example can be helpful when gauging risk from Covid-19. If the risk of infection in your community is extremely high, think about what you would do if a hurricane were coming: stay home and stay safe. If the risk of infection in your community is high, think about what you would do in a thunderstorm: it is dangerous outside so you would go outside only when absolutely necessary. If the risk of infection in your community is moderate, think about what you would do in a heavy rainstorm: you probably wouldn’t go outside unless you are wearing a raincoat, rainboots, and brought an umbrella. The same goes for what you should do in the pandemic. Before going outside make sure you have a mask, gloves, and hand sanitizer. If there are near zero infections in your community, think of it as a bright sunny day: feel free to go out and enjoy. Even if Covid-19 risk in your community is extremely low right now, remember that just as the weather can change quickly so too can the risk of Covid-19 infection in your community. Brown University created a tool that uses zip code and activity type to assess the risk of different activities across the country.

A report recently released by the US Centers for Disease Control (CDC) further challenges the notion that Covid-19 only impacts older adults. Between January 26and October 3, 2020, the CDC estimates the US had 299,028 more deaths due to the pandemic than the typical number during the same period in previous years. Excess deaths are the deaths over and above what is expected in a certain time frame, using data from previous years as a baseline. Two-thirds of the excess deaths were attributed to Covid-19 while the other one-third were attributed to other causes. Excess deaths from the pandemic disproportionately affected people of color. The highest average increase in deaths over this period was found among Latinx people at 53.6 percent and among Black people at 32.9 percent. Most surprisingly, the largest percentage increases were among adults aged twenty-five to forty-four. In this age group there was a 26.5 percent increase in deaths. The high rate of excess death among twenty-five to forty-four- year olds serves as a stark reminder that the pandemic is having a tremendous negative effect on younger adults as well.

Until now, the extent to which children and younger adults can be infected with and spread the virus has been unclear. The new contact tracing study in India and data from the CDC confirms that children and young adults can be infected with and spread the virus. This additional knowledge can help both policymakers and individuals make choices to keep their families and communities safe. Making decisions based on evidence is the only way to avoid additional, unnecessary deaths from Covid-19.