Science’s COVID-19 reporting is supported by the Pulitzer Center.
The world is holding its breath.
After the novel coronavirus made its way from China around the world, one country after another adopted harsh measures to stop SARS-CoV-2 from spreading and overwhelming hospitals. They have hit the pause button on their economies and their citizens’ lives, stopping sports events, religious services, and other social gatherings. School closures in 188 countries affect more than 1.5 billion students. Borders are closed and businesses shuttered. While some countries are still seeing daily case numbers increase, others—first in Asia but increasingly in Europe—have managed to bend the curve, slowing the transmission of COVID-19.
But what is the exit strategy? “We’ve managed to get to the life raft,” says epidemiologist Marc Lipsitch of the Harvard T.H. Chan School of Public Health (HSPH). “But I’m really unclear how we will get to the shore.”
As they seek a path forward, governments around the world must triangulate the health of their citizens, the freedoms of their population, and economic constraints. Could schools be reopened? Restaurants? Bars? Can people go back to their offices? “How to relax the lockdown is not something around which there is a scientific consensus,” says Caroline Buckee, an epidemiologist at HSPH. Most researchers agree that reopening society will be a long haul, marked by trial and error. “It’s going to have to be something that we’re going to have to take baby steps with,” says Megan Coffee, an infectious disease researcher at New York University.
The number to watch in the next phase may no longer be the actual number of cases per day, but what epidemiologists call the effective reproduction number, or R, which denotes how many people the average infected person infects in turn. If R is above 1, the outbreak grows; below 1 it shrinks. The goal of the current lockdowns is to push R well below 1. Once the pandemic is tamed, countries can try to loosen restrictions while keeping R hovering around 1, when each infected person on average infects one other person, keeping the number of new cases steady.
To regulate R, “Governments will have to realize that there are basically three control knobs on the dashboard,” says Gabriel Leung, a modeler at the University of Hong Kong: isolating patients and tracing their contacts, border restrictions, and social distancing.