Flu Season Starts Early: What You Need to Know

If you’re surprised to hear about flu cases popping up before Halloween, you’re not alone. Experts say the 2026-2027 flu season is kicking off much earlier and more robustly than usual.

While influenza activity remains low on a national scale, cases are rapidly increasing in various regions, particularly in the West. Two states, Louisiana and Hawaii, have already recorded moderate flu activity.

As of October 21, flu infections are increasing or likely on the rise in 44 states, according to the latest estimates from the U.S. Centers for Disease Control and Prevention.

This trend is somewhat expected since flu activity usually begins to rise around this time of year. However, it’s notable that this year’s infections began climbing as early as August.

The CDC noted in its FluView surveillance report for the week ending October 17 that “early-season influenza activity is currently higher than typically observed at this time of year.”

Most of the cases so far have been attributed to the Influenza A H1N1 strain. This is a change from last winter when the H3N2 subclade K — often referred to as the “superflu” — was prevalent.

Additionally, the circulating H1N1 strain seems to have acquired a new mutation that may aid its ability to bypass existing immunity.

The H1N1 strain you may recall is the same one that caused the pandemic back in 2009.

As this mutated H1N1 strain spreads, healthcare professionals are encouraging everyone to get the 2026-2027 flu vaccine.

Why Is Flu Season Starting So Early?

No two flu seasons are identical; the timing and severity can vary from one year to the next. It’s still ambiguous whether this flu season will be more severe or how the mutated H1N1 strain will influence that, as noted by the CDC in a statement.

However, there are several signs pointing to an unusual increase in flu activity for this time of year.

According to the CDC, cases began climbing in late August and have maintained a steady rise since then.

The positivity rate for flu tests was 5.7% for the week ending October 17, compared to less than 1% during the same week last year.

Visits to outpatient facilities for flu-like symptoms reached 2.2% in the week ending October 17, exceeding the rates from the previous two seasons. There’s also been an uptick in hospitalizations and deaths due to flu-related issues.

Andrew Pekosz, a virologist at Johns Hopkins, remarked that while case numbers are currently low, we are still in the early stages of a flu surge.

The reasons behind this earlier-than-expected rise are not fully understood.

One theory suggests that people might have less immunity against the mutated H1N1 strain.

Dr. Bernard Camins, an infectious disease physician, mentioned that this could be why people are getting sick earlier than usual. The circulating H1N1 strain differs from the H3N2 strain that was prevalent last year, making some individuals, even those who had the flu last year, susceptible.

As the H1N1 cases started to rise in late August, the updated flu vaccines had only just begun to roll out. Pekosz adds that early-season flu often showcases the first strain that is the most effective at escaping immunity.

Does an early flu season mean it will be more severe? Not necessarily, according to experts. There’s still a lot to unfold regarding the trajectory of the 2026-2027 flu season, or whether it will be milder than the previous one, which was quite harsh due to the mutated H3N2 variant.

“We need to see how it evolves this year, but I think it’s just starting earlier,” Camins shared.

Dr. Natalie Azar, a medical contributor for NBC, wisely pointed out, “The only predictable thing about the flu is that it’s unpredictable.”

What Is the Mutated H1N1 Strain?

Influenza viruses are always mutating, which is why we receive updated flu vaccines every year.

During last summer, the H3N2 strain developed several mutations, leading to the emergence of the subclade K variant.

The CDC indicates that H1N1 virus variants typically undergo fewer mutations than H3N2 ones. However, this year’s H1N1 (pdm09), subclade D.3.1.1, has acquired a new mutation, G155E.

This particular mutation was first identified in September in Seattle.

Pekosz explains that this new strain is different from last year’s H1N1, and this specific mutation is crucial for generating protective antibody responses.

As a result, the current H1N1 strain might be better at evading immunity, meaning antibodies from past infections or vaccinations might not recognize it as effectively.

Yet, how this mutation will impact disease spread and severity remains unclear.

Even if the circulating H1N1 strain does not align with that included in the 2026-2027 vaccines, experts believe the shot can still offer some level of protection.

Pekosz emphasizes that a mismatch doesn’t equate to a total loss of immunity; it may just mean there’s reduced immunity.

Historically, H1N1 has significantly affected younger populations. Azar noted that the new mutation might make children more vulnerable, particularly if they haven’t encountered H1N1 before.

The CDC stated in its latest FluView report that it’s too soon to determine which viruses will dominate this season or if there will be any implications for flu vaccine effectiveness.

H1N1 Flu Symptoms

Flu symptoms often manifest suddenly and intensely, Camins explains.

Common symptoms of the flu include:

• Fever
• Chills
• Fatigue
• Body aches
• Runny nose
• Coughing

It’s important to note that distinguishing flu symptoms from COVID-19 can be tricky, which is why testing is essential, according to Camins.

If you test positive for influenza, antiviral treatments can help reduce both the severity and duration of illness.

These medications are particularly important for high-risk groups, like adults over 65, children under five, and individuals with compromised immune systems. They require a doctor’s prescription and need to be administered promptly within the first 48 hours of symptom onset to be most effective.

Contact your doctor if you experience severe flu symptoms.

When to Get the Flu Shot

Experts stress that there’s no need to panic about the mutated H1N1 strain, but it does serve as a reminder to protect oneself.

Pekosz recommends viewing this as a prompt to get vaccinated against the flu.

Receiving a flu shot effectively prevents severe illness, complications, and even death caused by the virus.

The 2026-2027 flu vaccines are widely available at pharmacies, doctors’ offices, and clinics. They offer protection against three viruses: H1N1 (pdm09), H3N2, and influenza B.

Various options are available, such as standard shots, high-dose versions, a nasal mist, and the new mRNA flu vaccine.

Pekosz notes that even if the vaccine doesn’t match a particular strain, it still protects against the other two strains included in the shot. Different strains can circulate later in the season; thus, the vaccine can keep you safe throughout winter and early spring.

While the flu shot isn’t 100% effective, Camins adds that vaccinated individuals will likely experience milder symptoms and much lower chances of hospitalization if they do contract the flu.

Vaccination is crucial for high-risk individuals, but everyone stands to gain from it.

Ideally, getting vaccinated before the end of October is best, but there’s still value in doing so later on.

Pekosz concludes that now is the right time to be vaccinated, especially since flu season is starting a bit earlier, and immunity from the vaccine takes about two weeks to develop.

If you’re uncertain about which flu vaccine to choose, consulting with your doctor or pharmacist is advisable.