Police officers stand guard outside St Thomas' hospital where Britain's Prime Minister Boris Johnson has been admitted receiving treatment for coronavirus, in London, Thursday, April 9, 2020. Johnson has spent his fourth night in the hospital's intensive care unit. 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/Kirsty Wigglesworth)