Gates, whose philanthropic efforts focus partly on health care, said China’s response to Covid-19 has been effective. “After January 23 when [China] realized how serious it was they did strong social isolation which made a huge difference,” he wrote. “Of course that isolation created a lot of difficulties for the people involved but they were able to stop the case spread.”

He also emphasized the importance of testing potential patients, citing China and South Korea as examples. “If a country does a good job with testing and ‘shut down’ then within 6-10 weeks they should see very few cases and be able to open back up,” he said.