President Joe Biden will make 400 million highly protective N95 masks available to Americans for free at pharmacies and community health centers around the U.S., a White House official said.

The masks will start to become available late next week, and the program will be fully up and running by early February, according to the official. The White House said the free masks are the largest deployment of personal protective equipment in U.S. history.

The Centers for Disease Control and Prevention, in updated guidance published last week, said N95 respirators are more effective at prevention transmission of the virus than cloth and surgical masks. However, CDC Director Dr. Rochelle Walensky has said wearing any mask is better than no mask.

The CDC said N95 masks must form a seal on the face to work properly, warning that gaps can let respiratory droplets that carry virus particles in and out of the mask. The CDC provided a factsheet to demonstrate how N95s should be worn.

The CDC recommends that everyone 2 years of age or older wear masks in indoors public spaces regardless of vaccination status in areas with substantial or high levels of viral transmission. Right now, virtually every county in the U.S. has transmission of the virus, according to the agency.

People are required by federal law to wear masks on planes, buses, trains and other forms of public transportation.

Democrats in Congress have pushed the Biden administration to provide N95 masks to Americans for free as the highly contagious omicron Covid variant has swept the country, causing unprecedented levels of infection. Sen. Bernie Sanders, I-Vt., reintroduced legislation last week to deliver three N95 masks to every person in the U.S. The legislation has 50 cosponsors in the House and Senate.

“Congress must demand the mass production and distribution of N95 masks, one of the most effective ways to stop the spread of the Covid virus,” Sanders said in a statement.

Researchers in Australia found that fabric masks are least 50% effective at filtering virus particles, while N95 and surgical masks are about 99% effective. The study was published in the peer-reviewed journal Pathogens in September 2020.

The Biden administration is also distributing free at-home Covid tests to American households. Every home can order four Covid tests at www.covidtests.gov.