Stage three trials, which are happening now, are what will tell us how effective the vaccines are. Yes, we'll learn more once it's released to the population at large, but we should have a pretty clear picture this year.
Event insurance typically excludes infectious diseases, and at present, they're all excluding it in big, bold letters. Events are proceeding anyway. The risk of liability for catching an infectious disease is pretty tiny, and as long as the event is being put on by an LLC, people aren't worried.
Sanctioning is also unnecessary, and easy to get in any event. Only a small minority of road races are sanctioned. If you want USATF sanctioning today, you just have to waive their insurance and buy it from a third party.