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But experts who have long championed for this most recent change say the update really pushes the need for good indoor ventilation to the forefront especially at a time when schools and offices are bringing people back to meet in person.

This is because ventilation, where indoor and outdoor air is exchanged, helps to ensure that the virus is not building up, thereby increasing the likelihood that others in the space will breathe it in, explains Linsey Marr, the Charles P. Lunsford professor of civil and environmental engineering at Virginia Tech and an expert in aerosol science. Her advice? If the weather allows it, open windows are great. If not, then it involves adjustments to the HVAC (heating, ventilation and air conditioning) system so you're bringing in as much outdoor air as possible, she tells AARP.

Opening windows can also keep your home environment healthy especially if you've having people over who are not part of your household, says Richard Corsi, dean of Portland State University's Maseeh College of Engineering & Computer Science and an expert on indoor air quality. Upgrading filters in indoor spaces aim for MERV 11, 12 or 13 and firing up portable high-efficiency particulate air (HEPA) cleaners can also lower the concentration of virus particles in the air, Corsi adds. (MERV, or minimum efficiency reporting value, ranges from 1 to 16; the higher the rating, the better the filter is at capturing smaller particles.)

Just make sure you select an air cleaner, also known as an air purifier, that is right for your space by paying attention to the clean air delivery rate (CADR): You want it to meet or exceed the square footage of the room. Let's say a room is 100 cubic feet. If the air cleaner only does 20 cubic feet per hour, that's not enough, Marr says. Look for the CADR rating on the cleaner itself or on its packaging, or check the manufacturer's website.

One more tool that works: Upper-room ultraviolet radiation, where you just sterilize the air, says Donald Milton, M.D., a professor of environmental and occupational health at University of Maryland's School of Public Health. This can be especially helpful in school lunchrooms, for example, where kids are eating without masks on, he says. The CDC notes this intervention also makes sense in areas where there's an increased likelihood of sick people like a hospital waiting room or school clinic.

Another takeaway from the CDC's latest update on COVID-19 transmission: Masks are still an important tool in indoor settings, especially if you are unvaccinated or not yet fully vaccinated. (Some experts encourage masks for everyone in indoor public spaces, especially if you are going to be around unvaccinated people, but the CDC on May 13 updated its guidelines to say that fully vaccinated individuals no longer need to wear a mask indoors, except in certain situations like in health care settings or on planes, trains, buses and other forms of public transportation. They should also be worn where required by local businesses and workplaces.)

Read more:

How the Coronavirus Spreads: Biggest Threats Are in Air, Not on Surfaces - AARP