The beginning of fall and back-to-school time means cold virus season has arrived. Usually, colds hit as lesser-evil infections before influenza season takes over. But already, the flu is popping up early in pockets of the U.S. Here’s why that might be and everything else you need to know as we head into the dreaded annual flu season.

According to the Centers of Disease Control and Prevention’s latest FluView report, released on October 9, flu activity has been climbing since early September. Flu season in the U.S. generally begins gaining momentum in the fall, with activity peaking between December and February. But surveillance indicators show that certain strains of influenza are rising fast. The CDC’s latest data show a nationwide percent positivity rate for influenza—the percentage of all positive influenza tests—of 3.6 percent. That’s a sixfold increase compared with this time in 2025, when the rate was 0.6 percent.

Parts of the U.S. are showing much higher positive rates. The CDC splits the country up into regions, and Region 9, which includes Arizona, California, Hawaii and Nevada, had 9.5 percent positivity, according to the latest data. Experts say that is exceptionally high for this time of year.

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“It’s not unheard of to see things rising at this stage,” says Andrew Pekosz, an immunologist at the Johns Hopkins Bloomberg School of Public Health. “But it’s also something that we probably shouldn’t be seeing until maybe November or December at the earliest.”

Flu can be caused by different types of influenza, including influenza A (and its subtypes) and influenza B. Usually, flu season brings a mix of types. Right now, in the areas of the country with the highest positivity rates, H1N1, a subtype of influenza A, is dominant. According to the CDC, the most recent weekly testing data showed that 98.4 percent of the positive tests indicated H1N1 and that 1.6 percent revealed H3N2, another influenza A subtype.

Still, experts say it’s too early to predict whether these spikes could signal a particularly severe winter flu season.

Will this year’s flu vaccines work well?

One of the best ways to protect yourself from the flu is to get a flu vaccine. Every year experts reformulate these vaccines depending on what strains of the virus are circulating or predicted to circulate during the coming winter season.

Whichever subtype dominates matters because it can help predict which groups will experience the greatest disease burden. It can also determine how well existing immunity will protect people, as well as how the year’s flu vaccines will perform.

H1N1 and H3N2 are both influenza A subtypes, but they are evolutionarily distinct and can affect people differently. H3N2-dominant seasons have historically been associated with particularly severe illness among older adults. H1N1, on the other hand, has had a greater effect on younger populations—but both can cause serious disease at any age.

“The version [of H1N1] that’s circulating seems to be a little bit different from the vaccine strain that we have and from H1N1 strains that have circulated before. It’s what we call an antigenic drift,” Pekosz says. That could be why the virus is emerging so early, he adds. If it can evade prior immunity, the pathogen will be easier to transmit.

But it’s still too early to know how that might influence the effectiveness of the current flu vaccines.

When is the best time to get vaccinated?

Trish Perl, a professor of internal medicine and a specialist in infectious disease at UT Southwestern Medical Center, says that right now is the best time to get a flu shot.

“Immunity from the flu vaccine is strongest for about four to six months, and we usually expect flu to peak in December or January,” Pekosz says. “So a September or October vaccination will get you through the worst part of the flu season.”

Perl agrees—she says that she often tells her people to, at the very least, get a flu vaccine before Thanksgiving. Because after that, she says, people have unlimited excuses for why they can’t find the time.

And with certain areas already seeing spikes, getting the shot earlier than usual may be best, Pekosz adds.

“The best time to get vaccinated is before you see influenza in your area,” he says.

What about the newly approved mRNA vaccine for flu?

On August 5, 2026, the Food and Drug Administration approved Moderna’s mFLUSIVA, the first mRNA seasonal influenza vaccine, for adults aged 50 and older. In a phase 3 clinical trial, the vaccine was found to be 26.6 percent more effective at preventing the flu than a standard flu shot.

FDA approval and inclusion in federal vaccination recommendations—informed by guidance by the CDC’s Advisory Committee on Immunization Practices (ACIP)—are separate regulatory steps, however. The disruption to ACIP under the Trump administration has made incorporating newly approved vaccines into guidance more complicated.

Moderna had said the vaccine would be available at select retailers during the 2026–2027 flu season. But so far, access appears to be limited.

Experts, including Pekosz and Perl, say that if people who qualify for the new mRNA vaccine have access to it, they should consider it. “The data would suggest that if you can get the mRNA vaccine, you probably will get a stronger response to most of the components in the vaccine than if you get the standard one. But again, the standard one is pretty good as well,” Pekosz says.

He and Perl are optimistic about the potential of mRNA technology to improve flu vaccines in the future. Because mRNA vaccines can be developed and manufactured more quickly than traditional shots, scientists could wait until later in the year before selecting which influenza strains to target. That added time could help us better predict which strains will circulate during flu season—ultimately meaning more effective vaccines.

The best thing anyone can do right now is to get their flu shot as soon as possible. And if you do end up getting sick, Perl says not to forget about antivirals, such as Tamiflu, which can be very effective and, in many cases, could reduce the amount of time you are infectious.