Is it COVID or the flu? New tests can check for both.

Yet again this winter, millions of Americans will wonder if a nagging cough or body aches is a sign they’re coming down with COVID-19 or the flu. This time, they’ll have an expanded array of tools to get an answer without leaving the house.

There are now nine at-home tests that can detect the coronavirus and influenza at the same time. Many of the tests, which can be sold over the counter, were just approved in the past six months.

“It’s really a big shift in what’s available,” said Dr. Gregory Martin, a professor at Emory University School of Medicine in Atlanta.

The Food and Drug Administration approved most of the COVID-and-flu combination tests under emergency protocols in 2023 and 2024. Earlier this month, the agency also authorized the first of these combination tests, made by the health care equipment company Healgen, under its traditional, more rigorous approval process.

The combination tests look and work a lot like traditional at-home COVID tests: They’re easy to use and fast, often delivering results within 15 minutes. Most are only slightly more expensive than regular COVID tests, usually hovering around $30 for a pack of two, although they may not be covered by insurance.

Doctors say the combination tests could be vital as we head into colder months and peak virus season — but only if more people know to use them, or that the tests exist at all.

Many of the combination tests check for COVID and two common flu viruses, influenza A and influenza B, making the products a tidy three-in-one package.

A negative result does not rule out an infection, but doctors said the combination tests are about as effective as those that are only for COVID. The FDA has said it expects at-home COVID tests to detect the virus at least 80% of the time when someone is infected.

Most of the new products are antigen tests, meaning they pick up on specific proteins in the viruses. Only one, made by Pfizer, is a molecular test, which is more sensitive because it searches for genetic material. That test is pricier, at around $40.

Many combination tests function just like regular at-home COVID tests: Typically you swab the inside of your nostril, dunk it in a solution and squeeze droplets of the mixture onto a test strip.

As with at-home COVID-only tests, the combination tests likely work best when you have symptoms. If you are vulnerable to COVID or the flu, you may want to test as soon as you feel ill, said Dr. Davey Smith, an infectious disease specialist at the University of California, San Diego.

That’s because the antiviral medications that can reduce the risk of severe cases of COVID and the flu, like Paxlovid and Tamiflu, need to be taken early on.

It’s also crucial to test more than once with the combination tests, and at least 48 hours after the first try if the result is negative, said Nathaniel Hafer, an associate professor of molecular medicine at UMass Chan Medical School. The more you’ve been exposed to the coronavirus, the better your body gets at recognizing it, triggering symptoms as the immune system combats the infection. You can have a hacking cough and full-body fatigue for days before enough virus has built up in your nose to turn a test positive.

If your first test is negative, but your symptoms worsen within 48 hours, there’s an increased chance that you’re sick with COVID or the flu, Smith said.

If you have symptoms and can afford and find a combination test, doctors say to use it in most cases, since it’s challenging to distinguish COVID from the flu based on symptoms alone. But there are a few circumstances in which a regular COVID test may make more sense.

The flu follows a predictable annual pattern: You can get infected year-round, but the virus typically peaks between December and February. If you’re sniffling or wheezing in July, you can probably reach for a regular COVID test, said Dr. Heba Mostafa, a pathologist at the Johns Hopkins University School of Medicine.

And context matters. If you wake up with a sore throat and learn that a friend you just spent time with tested positive for the coronavirus, a plain old COVID test will probably do the trick.