Those who have had MMR vaccine (measles, mumps and rubella), and in particular, the mumps vaccine, may have protection against more severe forms of Covid-19. (What about weird people like me who actually had both measles and mumps?) They theorize this could be why younger people have fewer cases and less bad outcomes – because so many have had the MMR vaccine.
Those who received a TB vaccine in the past may also have a form of protective immunity to Covid-19.
Finally, researchers have developed a simple nasal spray that coats virus particles inside the nose so that the virus is unable to penetrate into human cells. Because the two common compounds are already approved for use, this could be deployed and distributed quickly once trials are completed.