#: Why do you test negative on an antigen test with COVID-19 symptoms? Do you have flu? Not necessarily — here’s why

You isolate for at least 5 full days — day zero being the first day of symptoms — because that’s the responsible thing to do. Yet you still have your sense of taste and smell. You don’t want to infect others, and still your antigen tests come up negative.

As the omicron variant sweeps across the world, and flu season takes hold, how can you tell the difference? Until you finally get that positive COVID-19 antigen test — if you’re lucky enough to find one — the truth is it’s almost impossible to tell.

“Get vaccinated, get boosted, wear a mask in public indoor settings in areas of substantial and high community transmission, and take a test before you gather,” says Rochelle Walensky, director of the U.S. Centers for Disease Control & Prevention.

COVID-19 and flu symptoms are practically the same

But how do you know if you have the flu or COVID-19? Both may involve fever, cough, shortness of breath/difficulty breathing, fatigue, sore throat, runny or stuffy nose, body aches, headache, vomiting, diarrhea, change in or loss of taste or smell.

The CDC says a loss or change in taste or smell is more common in COVID-19, but it’s not a precondition for having omicron, the highly transmittable variant that’s blazing a trail across schools, workplaces and family gatherings.

Omicron and delta pose a greater threat for those who are not vaccinated, but a persistent dry cough and shortness of breath are clearly two symptoms that could point to COVID-19, especially if you were exposed to someone who tested positive.

Do you see the Catch 22? The flu and COVID-19 have near identical symptoms. Despite all the guidelines helping people to distinguish between the two, a positive rapid antigen test is still the only surefire way of knowing which illness you have.

Repeatedly testing negative with COVID-19 or flu symptoms

Those tests are not one and done. Someone with COVID-19 and suffering from symptoms may still test negative on antigen tests for 1-3 days before the virus grows. However, Michael Mina, an epidemiologist, contends that is a good thing.

Vaccines help our immune system recognize and fight the virus, and that creates symptoms. “This is expected,” he wrote on Twitter. “Symptoms don’t = contagious virus. This is literally a reflection of the fact that vaccines are doing their job!”

That’s why we feel horrible even when we’re negative. “We recognize the virus quickly after it lands in us, we develop symptoms, we kind of fight it off, then it often eventually wins, and grows fast AFTER immunity/symptoms started,” he added.

“Thus, if you are symptomatic and negative — although it means you’re probably not contagious at that moment, be very very cautious,” Mina adds. “Quarantine even if possible and test the next morning or that night. (Sometimes even longer.)”

Isolate and test with symptoms. But when do you exit isolation?

How do you interpret those rapid tests? One red line is negative, while two red lines means positive. A stronger second red line likely means you’re at your most infectious. A lighter red line means you’re at the beginning or end of your infection.

When and how you exit isolation has just gotten trickier. The CDC is maintaining its position on its isolation policy, instructing people who had symptoms and who have access to a test to take one before exiting isolation. But it does not require it.

Even if you are less contagious after your symptoms have alleviated, the CDC’s critics argue that this creates another gray area of confusion, and puts the onus on the individual to make decisions that are best left up to public-health officials.

The CDC’s explanation: “The majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after.” That, however, was before omicron spread like wildfire.

This stance has divided public opinion, and frustrated some epidemiologists. Many public-health advocates say it’s safer to get that negative antigen test before going out into the world. For his part, Mina called the CDC guidelines “reckless.”