Starting Thursday, every US household can again order up to four free rapid test kits by mail  for a limited time, part of  the White House’s efforts to fight a potential surge in cases this winter. Covid cases, hospitalizations and deaths are rising, according to the Centers for Disease Control and Prevention’s daily tracker. Public health experts are also worried about cases of respiratory syncytial virus, or RSV, and flu hospitalizations are at their highest rate in more than a decade.

“We don’t want this winter to look like last winter or the winter before,” said Covid-19 Response Coordinator Ashish Jha at a press briefing on Thursday. The program will  provide “another easy option to access testing when there’s a greater need, like there is right now.”

The administration is urging people to test when they have symptoms, before and after traveling during the holiday season or visiting indoors with immunocompromised or vulnerable people. The tests will begin being shipped on Dec. 19, according to the White House. But how long are they good for? 

The Food and Drug Administration has extended the shelf-lives of 14 brands of tests. Consumers can look up their specific brand and even the lot number to see the correct expiration dates. Brands including iHealth, from a subsidiary of Andon Health in China, Abbott Laboratories’ BinaxNow and ACON Labs Inc.’s Flowfex now last up to 12  months, 15 months and 21 months, respectively.

The FDA advises against using at-home Covid tests past their expiration date, because tests and their parts can break down over time. The agency typically authorizes at-home tests for four to six months and extends the expiration date after the company conducts a study. However, some state health officials have said that at-home tests can be used after their expiration date. Test kits include information about built-in quality controls, like the pink-purple line on Abbott’s BinaxNow test.

For people who test positive at home, there’s now a website to report results anonymously. CareEvolution, a health-care technology company, and the National Institutes of Health launched a website on Nov. 22, called Make My Test Count.

In the meantime, experts  recommend taking preventative steps to reduce risk of illness. The New York City Department of Health and Mental Hygiene again recommends masking in public indoor settings and crowded outdoor settings. Los Angeles and Oregon have done the same. 

The administration has asked Congress for more funding for its Covid response, but so far that request hasn’t been fulfilled. The US is providing the tests with the stock it has left after pausing the program this summer and leftover money from the American Rescue Plan.