Free, mail-order COVID tests are back. Here’s how to get them and when to use them.

With waste water numbers climbing again, experts urge families to test before gathering.

Rapid antigen tests for COVID-19.DAVID GANNON/AFP via Getty Images

The federal government’s free COVID-19 testing program, which resumed on Thursday, gives people easier access to a safety tool that experts say can be especially important during the holidays.

Every household can order up to four tests at COVID.gov/tests and receive rapid antigen tests in the mail.

Rapid antigen tests detect proteins found on the outside of the virus. They are the best way to find out if you are infectious.

When families get together for the holidays, especially if older or otherwise vulnerable people are present, it makes sense for everyone to test right before the gathering, experts say. If those who test positive stay away, the likelihood of spread is greatly reduced, while those who test negative can feel reasonably comfortable that they won’t get anyone sick.

“It is a good strategy,” said Dr. Amy Barczak, infectious disease specialist at Massachusetts General Hospital. “It’s easily available, and everyone can choose to do it, and hosts can make tests available to people who are getting together.”

William Hanage, codirector of the Center for Communicable Disease Dynamics at Harvard T.H. Chan School of Public Health, said that when he visits his parents in the United Kingdom next week, “I’m certainly going to be carrying a bunch of rapid tests with me, and doing it just before I meet up with them.”

Barczak and Hanage made their comments Wednesday at a briefing titled “COVID-19′s Shifting Landscape,” held by Harvard Medical School’s Massachusetts Consortium on Pathogen Readiness.

One of those shifts – rising COVID-19 cases, hospitalizations, and deaths – prompted the Biden administration to resume mailing the free tests, a program that paused in September after distributing more than 600 million tests. (The pause came out of fear that tests would run out before the winter surge. The administration reportedly has found another source of funding.)

In addition to ordering tests through the federal program, you can buy them at many pharmacies, and they are often free if you have health insurance. Additionally, the state maintains a list of in-person testing sites at https://www.mass.gov/info-details/find-a-covid-19-test.

Nationally, said Dr. Jacob Lemieux, infectious disease specialist at Massachusetts General Hospital, “We’re seeing these [upward] trends across the board in the test positivity rate and the hospitalization rate and, alarmingly, also in the death rate.”

With so many people testing at home, the official case counts are considered unreliable. But the amount of virus detected in waste water is a good indication – and those numbers in Massachusetts are at the highest they’ve been in nine months, Lemieux said. They’re still nowhere near as high as last winter.

“Given that the waste water is a leading indicator by about a week or two, it’s reasonable to anticipate, at least in Massachusetts, that case counts will rise,” Lemieux said at the briefing.

Data from the Massachusetts Department of Public Health show that the number of people hospitalized with COVID-19 – the count was 674 on Dec. 7 – has been increasing sharply since Thanksgiving. But the count is still lower than in October, and almost one-fifth of the number seen in January, 2022, the height of the first Omicron surge.

The number of deaths in Massachusetts has fluctuated some, but has been at about the same level since May, with four to nine deaths per day.

The “happy part” of the evolution of SARS-COV2 is that many people are protected against severe disease and death, said Dr. Jeremy Luban, professor of molecular medicine, biochemistry, & molecular biotechnology at UMass Chan Medical School. ”The immunity that’s elicited by the vaccinations, and/or from prior infection, seems to be quite protective, and there’s no evidence that the virus is evolving away from those immune protective mechanisms,” he said at the briefing.

But at the same time, the virus seems to have an “infinite ability” to keep spawning new varieties that can evade the antibodies that prevent infection, Luban said. As with other coronaviruses, he said, “We can see waves of these viruses coming back every two or three years, despite people having neutralizing antibodies against the previous forms.”