Humans tend to think of illness as a binary. You are sick or you aren’t, which feels simple and knowable. In reality, most types of communicable disease are far less black and white: People are infected before they become aware that they’re sick. For much of the outbreak in the United States, local officials have asked people who suspect that they have COVID-19 but aren’t having serious trouble breathing to avoid seeking medical attention. That means that by the time most infections become official cases, people have spent days or weeks trying to heal on their own before seeking care. The periods of information lag with COVID-19 are longer than those of the colds and flus to which it’s often compared, which has been a central problem in containing the virus since the beginning. In order to make predictions and policy from any particular day’s case numbers, health experts have to synthesize information about testing rates, positive rates, local guidelines, and anything known about how people are responding to instructions to stay home or get back to business. And in order to make everyday decisions and assess their own risk, people have to live simultaneously in the past, present, and future.
Asking the general public to think in such broad and uncertain timescales is a tall order. “The concept of an incubation period or the onset of severe disease—those aren’t things that the public is well versed in, nor should we expect them to be,” says Tom Hipper, who manages the Center for Public Health Readiness and Communication at Drexel University. As a result, keeping the slow progression of a disease in mind can be difficult for regular people trying to make sense of official statistics. “As humans, I think we like instant gratification and we like instant feedback on things,” Hipper told me. The lull between new behavior and its measurable results “can make it a little more difficult to see the connection.”
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The snail’s pace at which COVID-19 infections seem to run their course makes public-health communications about the state of the current outbreak unusually complicated. The available evidence suggests that it usually takes about five days for an infected person to go from transmission to symptoms, but it can take as long as 14 days, and the person infected will be contagious for much of that time. The flu, by comparison, goes from transmission to symptoms in an average of two days and a maximum of four, according to the Centers for Disease Control and Prevention, and most people are infectious for only about a day before becoming ill.
Public-health experts can’t change the pace at which COVID-19 moves once a person is infected, but information doesn’t have to be delayed as much as it currently is in the U.S. The speed at which cases of the disease become known to the medical system, government monitors, and the general public depends on how hard a state or country is trying to find them. So far, the best-case scenario seems to be what’s happened in South Korea. In January and February, as the situation in Wuhan, China, deteriorated, South Korea quickly began identifying and isolating infectious travelers from the country, seeking the contacts of known cases, and testing those people before they became symptomatic. This program of testing, tracing, and swift isolation meant South Korea had something closer to real-time information about how the disease was spreading within its borders, and it was able to control the outbreak quickly. Such proactive approaches allowed South Korea, Germany, and Hong Kong to relax some of their restrictions on business and travel, and to quickly identify any new outbreaks that resulted. But even with those measures, all have experienced an uptick in new cases after reopening.