Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission.
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.
Travel requirements to enter the United States are changing, starting November 8, 2021. More information is available here.

Interactive Ventilation Tool

Interactive Ventilation Tool

Small particles that people breathe out can contain virus particles, including the virus that causes COVID-19.  If a guest visits your home, improving ventilation (air flow) can help prevent virus particles from accumulating in the air. Good ventilation, along with other preventive actions, like staying 6 feet apart and correctly wearing masks, can help prevent you from getting and spreading COVID-19.

How can I decrease the level of virus particles during and after a guest visits my home?

Select the options below to see how particle levels change as you adjust ventilation settings.

(To create additional scenarios, including to adjust the length of the visit and size of the home, see the expanded model from the National Institute of Standards and Technologyexternal icon.)

This tool uses modeling data from the National Institute of Standards and Technologyexternal icon. The results are estimates and might not be exact in the real world. Our model assumes a visitor is staying for 4 hours in a 1,000 square-foot space and is not wearing a mask. This size is used because 1,000 square feet is the size of an average one-bedroom apartment in the United States, or about one floor of a larger home. The particle reduction is calculated based on levels that would be in the air at the end of the visit. If the “Open Window” option is selected as “Yes,” the tool assumes one single open window. All scenarios are compared against a scenario with no open windows, no HEPA air cleaner, and no HVAC system use.

For this model, a “premium” filter is based on one rated for MERV 13 filtration and “regular” filter is based on MERV 6 filtration. Learn more about HVAC filters and portable air cleaners. Visit Ventilation in Buildings (item #3 in Ventilation FAQs) to learn more about MERV ratings.