Early reports out of China showed that elderly people and the chronically ill were most vulnerable to Covid-19. Yet an alarming number of young people in the United States have been hospitalized with severe infections. According to the Centers for Disease Control and Prevention, nearly 40% of American Covid-19 patients who were hospitalized were under 55 – and 20% were between ages 20 and 44. And in rare cases, even children have died after falling ill with Covid-19. Three experts interpret the data. Are more young people falling severely ill with Covid-19 than expected? Dr Timothy Brewer: The data have actually been pretty consistent across lots of different countries. Initially, people were very focused on mortality rates, and death rates in young adults are low pretty much everywhere you look. And I think people interpreted that to mean that young adults were not getting infected, and were not getting severely ill. As more data came out about hospitalizations and infection rates, we learned that was not the case. A recent study out of Shenzhen, China, showed that young people are just as likely to get infected as older individuals. Now that we’re seeing more data on hospitalization rates, we’re seeing that yes, young adults are experiencing severe illnesses. The big difference between them and older adults is [young adults’] mortality rates tend to be lower. Dr Edith Bracho-Sanchez: Adults and people with underlying medical conditions are, without a doubt, the most severely impacted by this. But the American public, as a whole, has wide-ranging levels of underlying baseline health. Close to two out of every 10 kids in this country are obese; nearly four out of every 10 young adults are. And that’s just one baseline measure of health in the American public. Unfortunately in America, not all our population is in top-shape health. Dr Christopher J L Murray: We have grave concerns with overinterpreting the reported case rates because it’s very much a function of who gets tested. In some places, like here in the US, [mostly] old people were being tested. So we’ve largely been looking at the death data. What we do know is that the population death rate [in people] below age 50 is dramatically lower than 80 and older. There’s a lot of lag in data. So we’ve got a pretty good handle on confirmed cases and deaths, but age breakdowns and hospitalization data are really patchy at this point. How exactly do specific health issues – such as vaping or obesity – modulate someone’s susceptibility to a serious infection? Murray: We just don’t know. We need to see more specific data to understand that. Are lower death rates among young people a function of shortages and physicians allocating scarce resources to the young? Brewer: There is a big variation in mortality rates overall across countries. In the US mortality rates are about 1.5%. In Italy, they’re around 9%. In South Korea, they’re under 1%, and in Germany, they’re under 0.5%. Some of that has to do with whether your healthcare systems are overwhelmed, and some of it will be the age distribution of the population. Italy has an older population, for example, than the United States or South Korea. Have you seen serious Covid-19 illnesses in pediatrics? Bracho-Sanchez: Yes, I’ve sent a few children to the hospital. It’s been consistent with what the national and international data is showing; the kids that I have sent to the hospital have had underlying medical conditions that make them immunocompromised. While it is true that the majority will have a mild illness, there are some kids and young adults who will have a very severe illness, and that cannot be emphasized enough. Does that change the way public health professionals try to communicate with the public? Bracho-Sanchez: Just like any other age group, there can be a wide range of manifestations of this virus. What do we understand about the recovery and potential long-term effects of a severe infection? Brewer: It takes people a lot longer to recover from this than we thought. We’ll have to see long term, but one of the things we learned from tuberculosis – which is a totally different pathogen – is that even if you cure the tuberculosis, a lot of people are left with long-term lung damage. And that’s very much a concern with Covid-19, and it’s something we’ll learn about going forward. Experts: Dr Edith Bracho-Sanchez, assistant professor of pediatrics and director of pediatric telemedicine at Columbia University-New York Presbyterian Morgan Stanley children’s hospital Dr Timothy Brewer, professor of epidemiology at the UCLA Fielding school of public health and of medicine, and a member of the division of infectious diseases, at the David Geffen school of medicine at UCLA Dr Christopher J L Murray, institute director of the Institute for Health Metrics and Evaluation (IHME), professor and chair of health metrics sciences at the University of Washington