At a Glance
- A new H3N2 subclade “subclade K” is spreading this season.
- Vaccines still reduce severe outcomes despite a strain mismatch.
- At-home flu tests are widely available but have limited sensitivity.
- Why it matters: Early detection and treatment can lower hospitalizations and help you decide when to stay home.
The flu season is heating up with a new H3N2 subclade, and while vaccines remain valuable, at-home tests offer a quick way to spot infection-though their accuracy varies.
New Flu Variant
Dr. Benjamin Bradley explains that the emerging subclade K does not match the strains in this season’s vaccines. He notes that data from other countries show vaccines still lower the risk of severe complications such as hospitalization and death.
At-Home Flu Tests
The FDA authorized the first combined flu-COVID home test kits in 2023 and a rapid antigen version in late 2024, making them available at drugstores.
- Sensitivity within 72 hours of symptom onset: 63% (2022 study).
- Sensitivity of a rapid combined COVID-flu-RSV test: 54%.
- First authorized test identified 90.5%-92% of flu A and B cases.
Dr. Benjamin Bradley stated:
> “You want to take (the test) as soon as you become symptomatic,” he said.
Dr. Sheldon Campbell noted:
> “That means way less than all of the people with the flu will test positive with an antigen test,” he said.
Timing is critical: take the test within the first one to two days after symptoms begin for the best accuracy.
How Tests Work
At-home tests detect viral antigens in nasal fluid and can distinguish between influenza A and B. This can help identify the new H3N2 variant, which is an A strain.
Dr. Benjamin Bradley said:
> “Flu viruses are built a little bit differently, so we’re able to at least separate out those two from one another,” he explained.
Interpreting Results
A negative result may be due to improper technique or timing. Ensure a good sample and, if symptoms persist, consider other respiratory viruses such as RSV, pertussis, or bacterial pneumonia.
Dr. Sheldon Campbell warned:
> “If it’s negative, you shouldn’t be done,” he said.
A positive result means you have the flu. Seek antiviral medication within 48 hours for the best chance of reducing symptoms.
Dr. Benjamin Bradley added:
> “Those drugs are most effective within the first 48 hours,” he said.
| Test Type | Sensitivity (within 72h) | FDA Reported Accuracy |
|---|---|---|
| Home Antigen | 63% | 90.5%-92% |
| Combined Rapid | 54% | – |
Key Takeaways
- The new H3N2 subclade K is circulating this season.
- Vaccines still protect against severe outcomes despite a mismatch.
- At-home flu tests are convenient but have limited sensitivity; timing matters.
Early testing and treatment can reduce complications and help you stay safe during this busy flu season.
