Should people who aren’t sick be tested for Covid-19? In August the Centers for Disease and Control Prevention revised its guidance to suggest focusing on the elderly and patients with symptoms. One may be excused for thinking that more testing is always better, but that isn’t true. Anyone can be infected with the virus, but there is a thousandfold difference in the risk of death between the young and the old. Testing strategy should reflect that.
There is little purpose in using tests to check asymptomatic children to see if it is safe for them to come to school. When children are infected, most are asymptomatic, and the mortality risk is lower than for the flu. While adult-to-adult and adult-to-child transmission is common, child-to-adult transmission isn’t. Children thus pose minimal risk to their teachers. If a child has a cough, a runny nose or other respiratory symptoms, he should stay home. You don’t need a test for that.
What would routine Covid-19 testing of children accomplish? A child with no symptoms who tests positive would be sent home and deprived of an education. Enough asymptomatic cases would lead to school closures. Yet the public-health consensus is that classroom learning is important, and closures are highly detrimental. That’s especially true for working-class children, whose parents can’t afford tutors or learning “pods,” but must instead make difficult choices between supervising their children’s education and paying the bills.
Sweden was the only major Western country that kept schools open for kids 15 and younger throughout the pandemic, with no masks or mass testing. How did it turn out? Zero Covid-19 deaths among 1.8 million children attending day care or school. Teachers didn’t have an excess infection risk compared with the average of other professions.
The results of reopening schools are also promising in England. Mark Woolhouse of the U.K. Scientific Advisory Committee for Emergencies, has said that “I agreed with lockdown as a short-term emergency response because we couldn’t think of anything better to do,” but “closing schools was not an epidemiologically sensible thing to do.” The U.K. “should have been concentrating on care homes.”
Israeli schools reopened in May, leading to a few outbreaks. But no child was hospitalized or died. An analysis of cellphone mobility data shows that in the weeks leading up to the school opening, Israel had all but returned to prepandemic activity. The Israeli school outbreak was more likely due to community transmission rather than opening classrooms.
As for higher education, most students who are infected will be asymptomatic or mildly symptomatic. If students experience symptoms, a reasonable response might be to confine them to their rooms. An unreasonable response would be to send them home to infect their parents and neighbors, who are at much higher risk than their college friends. Again, testing asymptomatic students would only create panic and pressure universities to close, with concomitant educational, economic and psychological harms.
To protect older teachers and professors or those with conditions that predispose them to high risk, schools and universities need to be flexible. Those instructors could teach remotely or grade exams with few face-to-face interactions.
Testing is intended to save lives, not to detect asymptomatic people who are otherwise healthy. The concept of a “school outbreak” is misleading, because it typically denotes a number of positive tests, not significant illnesses. The new CDC guidelines appropriately focus testing resources on hospital workers and the older generation. It is important to increase testing of hospital and nursing-home staff as well as visitors, so that family members can spend time with their older kin, for whom Covid-19 infection poses an unacceptable mortality risk.
Many countries have made the mistake of closing schools to protect low-risk children and teachers while neglecting the protection of those at high risk, especially in nursing homes. With the new CDC guidelines, strategic age-targeted viral testing will protect older people from deadly Covid-19 exposure and children and young adults from needless school closures.
Dr. Bhattacharya, a physician and economist, is a professor at Stanford Medical School. Mr. Kulldorff, a biostatistician, is a professor at Harvard Medical School.
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