At a Glance
- New H3N2 subclade K variant is circulating this season.
- Flu vaccines still protect against severe complications despite a mismatch.
- At-home antigen tests are available but have lower sensitivity than lab tests.
- Why it matters: Knowing how to use home tests and what the vaccine can do helps protect you during a severe flu season.
This flu season is unusually hard, driven by a new H3N2 subclade K and a mismatch with the vaccine. At-home flu antigen tests are now widely available, but their accuracy varies. Understanding how to use these tests and what the vaccine can still do is key to staying healthy.
Why This Flu Season Is Different
Dr. Benjamin Bradley says the new subclade K is a bit different from the strain in the current vaccine, creating a mismatch. However, data from other countries show the vaccine still helps prevent severe outcomes like hospitalization and death. The rise of the “super flu” strain is also driving higher case counts.
At-Home Flu Tests: How They Work and Their Accuracy
Like COVID tests, these tests look for viral proteins in a nasal sample. They can tell whether you have flu A or flu B. Their sensitivity is lower than lab PCR tests.
- 50-80% in kids, 50% or less in adults.
- 63% if performed within 72 hours of symptom onset.
- 54% for rapid combined COVID/flu/RSV test.
When and How to Test
Bradley says you should test as soon as symptoms start, which coincides with peak viral load. Testing after 72 hours reduces accuracy. Campbell recommends testing within the first one to two days.
- Take the test within 1-2 days of symptoms.
- Ensure a good sample from both nostrils.
- Follow the instructions carefully.
Dr. Sheldon Campbell says:
> “That means way less than all of the people with the flu will test positive with an antigen test,” he says.
Dr. Benjamin Bradley says:
> “You want to take (the test) as soon as you become symptomatic,” Bradley says.
Interpreting Results
A negative result does not rule out flu. Make sure the test was done correctly, and consider testing again after 24 hours if symptoms persist. If you still feel sick, other viruses like RSV or bacterial pneumonia may be the cause.
Dr. Sheldon Campbell says:
> “I’ve seen a world-renowned virologist do a rapid flu test wrong in front of a room of medical students,” Campbell says.
> “You really get up there and get some goop on the (swab) in both nostrils,” Campbell says.
A positive result means you likely have flu. Call a doctor within 48 hours to get antiviral medication, which can reduce symptoms. Watch for a rebound in symptoms that could signal bacterial pneumonia, a red flag to seek care.
Dr. Benjamin Bradley says:
> “Those drugs are most effective within the first 48 hours,” Bradley says.
> “If you can get that positive result early on, you can call up your doctor and get started on treatment, and that will hopefully reduce your symptoms.”
Dr. Sheldon Campbell says:
> “If it’s negative, you shouldn’t be done,” Campbell says.
> “Treatment could be the difference between going to the hospital or not, or dying or not,” he explains.
> “In that case, a home test is not what you want to rely on,” Campbell says.
Dr. Benjamin Bradley says:
> “If you start to feel better with the flu and then begin to feel worse again, that could be a sign of bacterial pneumonia, a serious complication that people sometimes get after the flu.”
> “That’s a red flag,” he says, “and that would be a reason to call your doctor.”
| Population | Sensitivity |
|---|---|
| Kids | 50-80% |
| Adults | ≤50% |
| Within 72 hrs | 63% |
| Rapid combined test | 54% |
Key Takeaways
- The new H3N2 subclade K variant is circulating this season.
- At-home antigen tests are useful but less sensitive than lab tests.
- Early testing and antiviral treatment can reduce severity.
By staying informed about the variant, vaccine benefits, and how to use at-home tests, you can better protect yourself and your loved ones during this tough flu season.
