A very encouraging piece of news. Though still a long ways off from being widely available and needs regulatory approvals first, Canada has already purchased 20 million doses (for 10 million people), it will help get this thing under control.
Maybe something the league can piggyback on when a vaccine becomes available
The decision would be at the discretion of the event organizer. A recent negative test would be another way to attend. League could use this get some/full fans back in the stands before herd immunity is reached.
You get tested and negative result
A) result is not even close to 100% accurate (not only do you have human / lab error but the test itself has issues in rapid test). You can show negative and be positive or vice versa.
B) even if you really are negative, you could walk outside clinic pass an infected person and bang you now have a certificate showing negative but you are really positive. The biggest issue with this virus is how transmissible it is. Even things like surface transmission while low chance do exist and certainly any sort of ventilation issue (eg walk through PATH to game, or take taxi, or share an elevator) and you now are infected and do not know it.
I was a little worried that Pfizer was touting that 90% figure a little too optimistically, but a second company seeing similar levels of effectiveness validates that this can really work. Go go modern science!