Here’s what we should be doing. First, bringing in more outdoor air in buildings with heating and ventilation systems (or opening windows in buildings that don’t) helps dilute airborne contaminants, making infection less likely. For years, we have been doing the opposite: sealing our windows shut and recirculating air. The result are schools and office buildings that are chronically underventilated. This not only gives a boost to disease transmission, including common scourges like the norovirus or the common flu, but also significantly impairs cognitive function.

A study published just last year found that ensuring even minimum levels of outdoor air ventilation reduced influenza transmission as much as having 50 percent to 60 percent of the people in a building vaccinated.

Buildings typically recirculate some air, which has been shown to lead to higher risk of infection during outbreaks, as contaminated air in one area is circulated to other parts of the building (as it did in the school with measles). When it’s very cold or very hot, the air coming out of the vent in a school classroom or office may be completely recirculated. That’s a recipe for disaster.

If air absolutely has to be recirculated, you can minimize cross-contamination by enhancing the level of filtration. Most buildings use low-grade filters that may capture less than 20 percent of viral particles. Most hospitals, though, use a filter with what’s known as a MERV rating of 13 or higher. And for good reason — they can capture more than 80 percent of airborne viral particles.

For buildings without mechanical ventilation systems, or if you want to supplement your building’s system in high-risk areas, portable air purifiers can also be effective at controlling airborne particle concentrations. Most quality portable air purifiers use HEPA filters, which capture 99.97 percent of particles.

These approaches are supported by empirical evidence. In my team’s recent work, just submitted for peer review, we found that for measles, a disease dominated by airborne transmission, a significant risk reduction can be achieved by increasing ventilation rates and enhancing filtration levels. (Measles comes with something that works even better that we don’t yet have for this coronavirus — a vaccine.)

There is also ample evidence that viruses survive better at low humidity — precisely what happens during winter, or in the summer in air-conditioned spaces. Some heating and ventilation systems are equipped to maintain humidity in the optimal range of 40 percent to 60 percent, but most are not. In that case, portable humidifiers can increase humidity in rooms, particularly in a home.