Science

South African National Defence Forces take up positions outside the hostel in a densely populated Alexandra township east of Johannesburg, South Africa, Saturday, March 28, 2020. South Africa went into a nationwide lockdown for 21 days in an effort to control the spread of the COVID-19 coronavirus. The new coronavirus causes mild or moderate symptoms for most people, but for some, especially older adults and people with existing health problems, it can cause more severe illness or death. (AP Photo/Themba Hadebe)

A women beats a cooking top in Geneva, Switzerland, Friday, March 20, 2020 during the 'Switzerland says thank you' campaign to thank paramedics who fight against the new coronavirus and the COVID-19 disease. For most people, the new coronavirus causes only mild or moderate symptoms. For some it can cause more severe illness. (Martial Trezzini/Keystone via AP)

This combination photo shows actors, from left, Laurence Fishburne, Matt Damon and Kate Winslet, who are among the stars of the 2011 thriller “Contagion” who have reunited for a series of public service announcements to warn about COVID-19. They have teamed up with scientists from Columbia University's Mailman School of Public Health to offer four individual homemade videos. (AP Photo)

A motorist rides past as residents talk on an alley at a low-income neighborhood in Jakarta, Indonesia, March 23, 2020. As the virus spreads, the World Health Organization has pointed out that the future of the pandemic will be determined by what happens in some of the world’s poorest and most densely populated countries. From Mumbai to Rio de Janeiro to Johannesburg the question is: What do you do if there is no space to socially distance yourself from others in some of world’s most unequal regions? (AP Photo/Dita Alangkara)

FILE - In this Wednesday, March 25, 2020 file photo Britain's Prime Minister Boris Johnson leaves 10 Downing Street for the House of Commons for his weekly Prime Ministers Questions, in London. British Prime Minister Boris Johnson has tested positive for the new coronavirus. Johnson's office said Friday March 27, 2020 that he was tested after showing mild symptoms, Downing St. says Johnson is self-isolating and continuing to lead the country's response to COVID-19. (AP Photo/Matt Dunham, File)

FILE - In this March 23, 2020 file photo, coffins are placed on scaffolding in the Crematorium Temple of Piacenza, northern Italy, awaiting cremation due to the coronavirus emergency. Italy is seeing a slight stabilizing in its confirmed coronavirus infections two weeks into the world’s most extreme nationwide shutdown, but the virus is taking its silent spread south after having ravaged the health care system in the north. For most people, the new coronavirus causes only mild or moderate symptoms. For some it can cause more severe illness, especially in older adults and people with existing health problems. (Claudio Furlan/LaPresse via AP)

FILE - This undated electron microscope image made available by the U.S. National Institutes of Health in February 2020 shows the virus that causes COVID-19. The sample was isolated from a patient in the U.S. Some political leaders are hailing a potential breakthrough in the fight against COVID-19: simple pin-prick blood tests or nasal swabs that can determine within minutes if someone has, or previously had, the virus. But some scientists have challenged their accuracy. (NIAID-RML via AP)

In this photo released by Saudi Press Agency, SPA, Saudi King Salman, chairs a video call of world leaders from the Group of 20 and other international bodies and organizations, from his office in Riyadh, Saudi Arabia, Thursday, March 26, 2020. The meeting is aimed at coordinating the global response to the fast-spreading coronavirus, which has shuttered businesses and forced well over a quarter of the world's population into home isolation. (Saudi Press Agency via AP)

In this Saturday, March 21, 2020 photo, a food delivery scooter passes Barbar Restaurant that now offers food for delivery only, after most of the shops and restaurants closed as part of the preventive measures against the coronavirus, in Beirut, Lebanon. Through 15 years of civil war and various bouts of violence since, Lebanon's Barbar eatery never closed its doors, forging ahead through difficult times while continuously serving up sandwiches to customers -- even if it meant doing so from behind sandbags during the conflict. (AP Photo/Bilal Hussein)

Medical workers oversee the disinfection of the streets to prevent the spread of coronavirus in Qamishli, Syria, Tuesday, March 24, 2020. (AP Photo/Baderkhan Ahmad)