Better ventilation can help make your home “COVID-safe”.

For two years you’ve beaten all odds. You masked yourself, kept your distance, got your shots.

Now, despite these efforts, you, your child, or someone else in your household has contracted COVID-19. And the last thing you want is for the virus to spread to everyone in the family or household. But how do you keep it from circulating when you live in a confined space?

The Centers for Disease Control and Prevention recommends isolating COVID-19 patients for at least five days, preferably in a separate room with access to a private bathroom, and scrupulously wearing masks for the patient and caregiver. But for many families, these are not easy options. Not everyone has an extra bedroom left, let alone a spare bathroom. Small children should not be left alone and the youngest do not tolerate masks.

“It’s quite difficult for parents of a young child not to be exposed,” said Dr. Preeti Malani, chief health officer at the University of Michigan. “You have to work back from perfect to possible and manage your risk as best you can.”

But take heart. Scientists say there is still a lot people can do to protect their families, most notably improving ventilation and filtering the air.

“Ventilation is very important,” said Dr. Amy Barczak, assistant professor of medicine at Harvard Medical School. “When you’re caring for someone at home, it’s really important to maximize any interventions that work.”

To understand why good ventilation can make a difference, it helps to understand how the novel coronavirus spreads. Scientists have learned a lot about its infection mechanisms in two years.

Viral particles float through the air like invisible second-hand smoke, dispersing on their way. Outside the home, viruses are quickly spread by the wind. Inside, germs can accumulate like clouds from thick cigarette smoke, increasing the risk of inhaling the virus.

The best strategy to avoid the virus is to match your indoor environment to the outdoor environment as much as possible.

Start by opening as many windows as the weather allows, said Joseph Fox, heating, ventilation and air conditioning engineer for a large school district in Ontario, Canada. If possible, open windows on opposite sides of the house to create a cross breeze that can help sweep viruses outside and bring fresh air inside.

For added protection, place a box ventilator in the patient’s window, facing out, to pull germ-laden air out. Seal any openings on the sides of the fan, said Jim Rosenthal, CEO of Tex-Air Filters, a company that makes air filter products in Fort Worth, Texas.

“It’s really easy and it’s cheap,” Rosenthal said.

To prevent infected air from seeping out of the sickroom, Fox suggests wedging towels in the crack under the bedroom door. You should also cover the ventilation grilles with plastic. These grills cover vents that draw air from the room and recirculate it through the heating or cooling system.

Fox also suggests turning on bathroom or kitchen exhaust fans, which can push germ air outside. Although leaving exhaust fans running while showering is relatively safe, Fox said it’s important to open windows if the fans are running for more than 10 minutes. This is to avoid depressurizing the house, a circumstance that could result in carbon monoxide being drawn into the house from the furnace or water heater.

Coronaviruses thrive in dry air, and increasing the humidity in the air can help deactivate them, said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech. Marr suggests increasing the humidity to around 40% to 60%.

Using portable air purifiers can provide additional protection. Research shows that high-efficiency particulate air filters, or HEPA filters, can remove coronavirus from the air. When people only have one HEPA filter, it’s best to place it in the hospital room to capture any virus the patient exhales.

“You want to place the filter as close to the source as possible [of the virus] as possible,” Fox said.

If affordable for families, additional air purifiers can be deployed in other rooms.

Store-bought air purifiers can be expensive, with some models costing hundreds of dollars. Yet for around $100, people can build their own portable air purifiers using a box fan, four high-efficiency air filters, and duct tape. These do-it-yourself devices were named Corsi-Rosenthal boxes after their co-inventors Rosenthal and Richard Corsi, dean of the College of Engineering at the University of California-Davis. The inexpensive boxes have been shown to work just as well as commercial air purifiers.

Rosenthal said the pandemic motivated him to help develop the air purifiers. “We are not helpless,” Rosenthal said. “We need to provide tools that people can use immediately to make things better.”

Although caring for a loved one through COVID-19 puts the caregiver at risk, the risk is much lower today than it was in the first year of the pandemic. An estimated 95% of the population has some immunity to the coronavirus due to vaccines, previous infections, or both, said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

Nonetheless, a recent study found that half of the people living in an infected patient’s household have also contracted the virus.

Given that older people and those with compromised immune systems are at higher risk from COVID-19, they might consider staying with a friend or neighbor if possible until the sick family member recovers, said Priya Duggal, a professor of Epidemiology at the Johns Hopkins Bloomberg School of Public Health.

Patients can be considered COVID-19-free after a negative PCR test, Barczak said. Because patients with even minute amounts of residual virus can still test positive on PCR tests for weeks long after symptoms have disappeared, patients can also use rapid antigen tests to assess their progress. If antigen tests are negative two days in a row, a person is considered less contagious.

KHN (Kaiser Health News) is a national newsroom producing in-depth journalism on health issues. Along with Policy Analysis and Polling, KHN is one of the three major operational programs at KFF (Kaiser Family Foundation). KFF is a donated non-profit organization that provides information on health issues to the nation.