What to Expect From the 2026-2027 Flu Season and How Severe It May Be, According to Virus Experts

Could this flu season turn out to be a rough one? Infectious disease specialists say there are a few key things everyone should know.

It is still too soon to know exactly what this flu season will bring, but experts often look to Australia for early hints about what may happen in the United States.

“We look very closely at Australia,” says Ryan Maves, MD, an infectious disease and critical care physician at Atrium Health Wake Forest Baptist. Because of similarities in population density and everyday behavior, flu trends in the Northern Hemisphere often resemble those seen in Australia.

This time, though, Australia offered an unexpected twist. Flu activity stayed fairly typical for most of the season, then surged unusually late as the country moved into spring. According to surveillance data from the Australian Centre for Disease Control, flu cases climbed more than 27% over a two-week stretch.

So should people in the U.S. expect a difficult flu season after this late-running spike abroad?

Will this flu season be bad?

So far, experts do not see signs of an especially severe season. In its respiratory-season outlook, the CDC projected a moderate flu season across all age groups, though the agency said its confidence in that forecast was only low to moderate.

A “moderate” season does not mean there is nothing to worry about. It is a formal CDC classification based on how peak flu-like illness, hospitalizations, and flu-related deaths compare with past seasons. That makes the forecast useful, but not definitive.

“It is hard to know which strains will dominate this season because the flu activity in the U.S. is still low,” says Majd Alsoubani, MD, MPH, an infectious disease physician at Tufts Medical Center. Still, the virus will return, and it can cause serious illness.

Experts also stress that many people underestimate influenza. The virus causes millions of illnesses and thousands of hospitalizations and deaths every year, and the CDC says the annual flu shot lowers the chance of a doctor visit for flu by 40% to 60%. Because no flu vaccine offers complete protection, vaccination rates are a major part of the question of how severe the season may become.

Vaccination also helps protect other people, not just the person who gets the shot. “Many of us don’t have chronic lung disease, don’t smoke, [and] are generally healthy,” Dr. Maves explains. “But unless you live in some extraordinary bubble, you have a parent, a grandparent, a child, a friend, someone you work with who does fit into one of those [high-risk] categories.”

Getting vaccinated helps protect them as well as you.

When does flu season usually happen?

In the United States, flu season generally runs from October through as late as May, with the peak usually falling between December and February.

Frederic Bertley, PhD, an immunologist and vaccine researcher, says he does not expect “a completely crazy flu season” this year. He anticipates something closer to the usual pattern, with the biggest wave likely landing between January and March, especially in colder northern regions. Even so, the CDC notes that the start, peak, and end of flu activity are difficult to predict, and Australia’s late surge is a reminder that the virus does not always follow a steady calendar.

How effective was last season’s flu shot?

The flu vaccine is never 100% effective at preventing infection, but that does not mean it fails.

Dr. Bertley explains that the challenge is how quickly influenza changes. Viruses such as measles mutate very slowly, which is why that vaccine is so reliable. Influenza evolves rapidly, so scientists must make their best evidence-based prediction about which strains will be circulating months later.

That problem became especially clear last season. A strain of influenza A(H3N2) called subclade K emerged after the vaccine for the previous season had already been designed, so it was not included in the formulation. By the end of the season, that strain had become dominant in the U.S., according to CDC data.

Even so, the vaccine still helped reduce illness. A CDC analysis found that vaccination lowered the risk of flu-related hospitalization by about 30% in adults and 41% in children and adolescents. That came during a season when vaccination rates were also down, with only about 46% of adults and 49% of children receiving a flu shot.

Jason E. Zucker, MD, of NewYork-Presbyterian/Columbia University Irving Medical Center, puts it simply: the goal of vaccination is not perfect protection, but reducing the risk of severe illness and complications, including hospitalization and death.

U.S. flu vaccines are also trivalent, meaning they target three influenza strains. If the match is off for one strain, the shot can still protect against the others.

What is different about this season’s flu vaccine?

According to the CDC, all three parts of the trivalent flu vaccine were updated this year to better match the viruses now circulating in the U.S. That includes a new component aimed at subclade K, which continues to circulate globally.

Updating all three components at once is uncommon, but it does happen, Dr. Alsoubani says. Usually only one or two components change from year to year, but this season scientists saw meaningful shifts across all three.

What flu shots are available?

This season’s flu vaccines all target the same three strains, but there are several options that may be better suited to different ages, health needs, or preferences.

In the U.S., flu shots generally fall into these groups:

• Standard flu shots: Traditional inactivated vaccines that are the main option for most people ages 6 months and older. For most adults under 65, the CDC does not recommend one brand over another.
• Higher-dose, adjuvanted, or recombinant vaccines: These are recommended for adults 65 and older because they may offer better protection in this age group. If none are available, the CDC says to receive another age-appropriate flu vaccine rather than wait.
• Nasal spray vaccine: FluMist uses weakened live influenza viruses and is approved for healthy people ages 2 through 49 who want to avoid a needle. It is not recommended during pregnancy or for people with certain medical conditions.
• mRNA flu vaccine: New this season, MFLUSIVA is the first mRNA flu vaccine approved in the U.S. for adults 50 and older.

One concern you no longer need to worry about is an egg allergy. The CDC says people with egg allergies can receive any flu vaccine that is otherwise appropriate for their age and health, without special precautions. Studies of the nasal spray and flu shots in people with and without egg allergies suggest that severe allergic reactions are unlikely.

The new mRNA flu vaccine

Dr. Bertley says one of the biggest developments this season is the arrival of mRNA technology for seasonal flu. The FDA approved Moderna’s MFLUSIVA for adults 50 and older, making it the first mRNA influenza vaccine approved in the U.S.

The concept is similar to mRNA COVID vaccines: mRNA gives your cells temporary instructions to create a harmless piece of the virus, which teaches the immune system what to recognize and fight.

Researchers are watching to see whether this approach may keep the immune system primed for longer and help protection last later into the flu season. Dr. Bertley says that remains a theory for now, and more real-world data will be needed as the vaccine is used more widely.

Still, a study from Washington University School of Medicine published in Nature Immunology suggested the mRNA flu shot may provide longer-lasting protection and broader coverage against different flu strains. That could make it more effective even if the virus changes during the season.

Another clinical trial, led by Moderna, found that the mRNA vaccine lowered illness risk in older adults by 26.6% compared with the standard flu shot.

When should you get vaccinated?

“Vaccines work best if they are given prior to exposure to the disease,” says Linda Yancey, MD, a board-certified infectious disease physician at Memorial Hermann Katy Hospital in Texas. “Getting a flu shot early in the season ensures that your immune system will have time to build immunity.” For most people, that means getting vaccinated in early fall, though it can still help if you get it later.

There are a few exceptions:

• Children who need two doses should get the first dose as soon as the vaccine is available so there is enough time to receive the second dose at least four weeks later.
• Pregnant women in their third trimester may also consider vaccination earlier to help protect their babies during the first months after birth.
• Older adults and pregnant women in their first or second trimester should generally avoid getting vaccinated too early, since protection can fade over the course of the season.

If the season is already underway, do not skip vaccination. The CDC recommends getting the flu shot as long as flu viruses are circulating, and later is still better than not getting vaccinated at all. In general, the flu, COVID, and RSV vaccines can also be given during the same visit.

COVID and RSV during flu season

COVID and RSV make flu forecasts more complicated, since all three respiratory viruses can circulate at the same time. “We’re still learning what seasonal COVID is going to be like,” Dr. Maves says. His concern is that even if influenza and COVID are not especially severe on their own, having several respiratory viruses circulating together can create a much larger public-health burden.

Vaccination remains one of the best ways to protect against these viruses:

• Flu: The CDC recommends the annual vaccine for everyone 6 months and older.
• COVID: The CDC recommends an updated COVID shot for all adults 18 and older and for children ages 6 months to 17 years who are at increased risk of severe illness; for other children, vaccination is based on shared clinical decision-making.
• RSV: The CDC recommends one dose for everyone 75 and older, and for adults ages 50 to 74 who are at increased risk of severe illness. Unlike flu and COVID, RSV is not currently an annual vaccine.

What to do if you get sick

If you develop flu-like symptoms, do not assume you can identify the virus by how you feel alone. Dr. Alsoubani says flu and COVID can both cause fever, cough, body aches, and fatigue, and symptoms by themselves cannot reliably tell one respiratory virus from another.

That is one reason testing matters, especially for people at higher risk of complications. Shira Doron, MD, chief infection control officer for Tufts Medicine and hospital epidemiologist at Tufts Medical Center, says people who may qualify for antivirals such as Paxlovid for COVID or Tamiflu for influenza should test early, because those drugs work best when started soon after symptoms begin.

Dr. Bertley adds that testing is also important because COVID is newer than the flu, and researchers are still learning about its longer-term effects. Knowing which virus you have can help guide treatment and prevention. Dr. Zucker says it can also help you decide when it is safe to visit friends or family members who may be more vulnerable, such as older adults, immunosuppressed people, or those with multiple medical conditions.

Whether you test positive for COVID or the flu, Dr. Zucker says you can return to normal activities once your symptoms have been improving overall for at least 24 hours and you no longer have a fever. Even then, the CDC advises extra precautions for the next five days because you may still be contagious. That includes good hand hygiene, wearing a mask, and giving others more space, especially indoors.

Once you feel better, you should still get vaccinated if you have not already. You can catch a different flu strain, and getting the illness does not provide the same cross-protection as the vaccine.