The NFL strongly believes that it’s much harder to transmit the coronavirus in an outdoor setting than in a confined indoor space. So what about domed stadiums, which technically are indoors?
As a source with knowledge of the league’s thinking explains it to PFT, open-air stadiums are the best for games with fans, and domes with retractable roofs should be opened whenever practical. However, domed stadiums can still work.
Per the source, NFL domes have ventilation systems with the capacity to circulate air effectively. They’ve been designed, for example, to clean our the air in the event of an aerosol attack from terrorists. Thus, the ventilation systems should be able to remove internal air and replace it with external air, fairly effectively.
So if, in a given state, county, and city, fans can attend a game, the fact that the game will be played in a dome shouldn’t keep fans from showing up -- even though it is better to play with no roof, if possible.