If you have respiratory symptoms as we head into winter and flu season, could it be COVID or the flu? Or something completely different?
Now we have one series of home tests who can distinguish between flu and COVID with one swab. They use technology that you may be used to. They are rapid antigen tests or RATs.
Here’s what you need to know about the tests, why they can be useful, and what they don’t tell us.
What’s new about these tests?
Most people were introduced to RATs while testing for COVID at home.
But there are RATs available to detect the flu yearalbeit used by healthcare professionals to test patients.
The latest RATs differ for two reasons. First, they detect both COVID and flu with one swab (a “combo” test). Two, they can be used at home.
The first of these flu/COVID combo home tests was approved in September 2022. Now there are several on the market.
With these tests you can check with one test kit whether you are infected with two types of flu (influenza A and B) and SARS-CoV-2 (the virus that causes COVID).
Read more: Are flu cases already 100 times higher than last year? Here’s what we really know about the 2023 flu season
How do they work?
These RATs contain antibodies that can detect influenza A, influenza B and SARS-CoV-2.
Some kits have a test cassette with one compartment to add drops and one window labeled: C (control), A (influenza A), B (influenza B), and T (test for COVID).
Some tests have two wells and two test windows. In one window you view the flu results and in the other the COVID results.
In the flu window you will see the markers C, A and B. If a line appears at A (and C), you have tested positive for flu A. If a line appears at B (and C), you are positive for flu B. If lines are visible at A, B, and C, you have tested positive for both flu A and B.
If A or B has a line but C does not, or if neither has a line, the test is invalid and you must take a new one.
The COVID window works the same way as in a standard RAT for COVID. If a line becomes visible at C and T, you are COVID-positive. If there is a line at C but not at T, you are COVID negative. If there is no line at C, the test is invalid.
Read more: Does my RAT really work? How do you know if your COVID test can detect Omicron?
Why take the test? 3 reasons
If you have respiratory symptoms, there are some practical reasons to know if you are positive for COVID or the flu.
First, knowing you have COVID will affect the timing of your booster vaccination. The Australian Technical Advisory Group on Immunization recommends that adults wait six months after a COVID infection to get a booster to extend the time you have protective immunity. So it helps to know if you are infected.
Two, if you need antiviral treatment, the medications differ depending on whether you have it flu or COVID.
Three: If you know you have the flu or COVID, you can take steps to protect others. Think of working from home, avoiding contact with vulnerable people and wearing a face mask in company.
Which key to use? When to use?
The Therapeutic Goods Administration (TGA) lists approved tests on its website. Type the term “combination” in the search box. All of the combo tests currently listed use nasal swabs to collect the sample.
Most are listed as “very highly sensitive”. This means that they achieve the same result in detecting positive cases as the gold standard PCR test 95% of the time. The others have “high sensitivity” (90% agreement with a PCR).
The best time to take the test is within four days of developing symptoms, as this is when it is easiest to detect both flu and COVID. The tests are more reliable if you have symptoms.
Read more: 15 things not to do when using a rapid antigen test, from storing it in the freezer to taking snot
What if I have symptoms but the test is negative?
One possibility is that your viral load was not high enough to be detected. You can take another test a day or so later to check again.
Another is that you may have another virus. Viruses that cause respiratory symptoms include rhinovirusesadenoviruses, respiratory sincytial virus And cold coronaviruses.
Other pathogens (disease-causing microorganisms) or health problems can also cause respiratory symptoms. If you are concerned, consult your doctor for medical advice.
Read more: Haven’t had COVID or a vaccine dose in the past six months? Consider taking a booster
What else should I know?
Since every test is different, make sure you follow the instructions for that specific test.
The price of combo kits advertised online ranges from A$8.95 to $59 (excluding delivery), so it pays to shop around.
It’s worth trying to prevent flu rather than testing for it later. Influenza vaccination reduces the chance that you will get the flu 40-60% when the vaccine is well matched to circulating strains. Flu vaccines for the 2023 flu season are now available.