One way it challenges old doctrine is that 1000ppm CO2 was considered good air quality in the past. Now it seems 800ppm or perhaps lower should be considered good air quality. They haven't tested other viruses yet (both colds and flu viruses are now considered airborne I understand, and other respiratory viruses probably are also), and each virus may react differently, so nobody actually knows yet what an optimal value is. It is even possible that the optimal CO2 value is somewhere below the current average concentration of CO2 in the air around the world when taking all airborne viruses into consideration, but nobody knows. More research is needed. But at least for covid, 1000ppm CO2 should probably no longer be considered good air quality (though replication of the study would be good.)