Expiration dates on at-home Covid tests deserve a close look. (Photo: Marc Levy)

Residents picking up free Covid antigen tests that the city began distributing Wednesday can’t dally in using them. They expire in no more than 29 days – on Jan. 26 – a city health department spokesperson confirmed.

“Residents can take as many rapid antigen tests as they need. But they should be aware that the tests expire near the end of January,” spokesperson Susan Feinberg said Wednesday.

Expiration dates printed on some of the IHealth test kits have much earlier dates, including some that have already passed, such as July 26. In July, the Food and Drug Administration extended expiration dates by six months for IHealth antigen tests.

A city announcement Thursday of the test distribution program included a link to an IHealth website where people can plug in the lot number on their test kit and get the new expiration date. The FDA also has a document that gives the extended expiration dates for each original expiration date. People can also check the expiration date using the QR code available at distribution sites, Feinberg said.

The tests come from the state, Feinberg said. The executive office of health and human services announced Sept. 7 that it would distribute 3.5 million test kits to cities and towns and that they would arrive by mid-October.

Asked when Cambridge got the tests, considering how soon they expire, Feinberg didn’t answer directly but said the city has already handed out tests in a “targeted” program. “For instance, our contact tracers arranged delivery of rapid tests to residents who test positive for Covid-19. We’ve delivered boxes of tests to the shelters and we gave out tests at [public health department] vaccine clinics, including the most recent one in December. The test kits were also made available to community organizations,” she said.

“We are anticipating a shipment of new tests from the state that will be available after January,” Feinberg said.

People should use the tests “when they feel sick, or if they are informed that they have been exposed to a person with Covid-19,” Feinberg said. Some public health officials have also recommended that people test themselves before visiting someone who faces increased risk from Covid because they are elderly or immunocompromised.

The city’s second day of giving out free test kits, two tests to a box, is Thursday at most libraries and at City Hall and the Cambridge Public Health Department. City officials previously said they had 60,000 tests to distribute.