Why This Year’s Flu Season Is Especially Dangerous and What the CDC Recommends

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Between September 2024 and April 2025, somewhere between 43 million and 73 million Americans caught the flu. Of those, up to 1.1 million ended up in hospitals. As many as 99,000 died. The peak weekly hospitalization rate hit 13.7 per 100,000 people—matching the worst week recorded since the CDC started systematic tracking in 2010.

By mid-December 2025, cumulative hospitalization rates were already the third-highest at this point in any season since 2010. Colorado reported 782 flu hospitalizations in a single week in late December—nearly 12 times what they’d seen in mid-November, and 300 more than their previous all-time seasonal peak. One pediatrician there described treating “steadily increasing numbers of kids with the flu with no end in sight.”

This is the version that fills emergency departments until wait times stretch past eight hours. That forces hospitals to postpone surgeries because they’ve converted operating rooms to overflow spaces. That kills children at rates we haven’t seen outside of the 2009 pandemic.

Hospitalization and Death Rates

The cumulative hospitalization rate reached 128.3 per 100,000 population through April 2025. That’s the highest in fifteen years of tracking. The Influenza Hospitalization Surveillance Network—which monitors about 9 percent of the U.S. population across different regions—counted 39,319 confirmed flu hospitalizations between October 2024 and April 2025. When extrapolated nationally through hospital reporting systems, this yields 545,026 hospitalizations.

In typical years since 2010, total seasonal hospitalizations have ranged from 120,000 to 710,000. Last season landed in the upper range.

280 children died from flu—the highest count since the CDC began tracking pediatric flu deaths in 2004, excluding only the 2009 pandemic when 288 children died. The median age was 7 years old. Infants under 6 months had the highest death rate at 11.1 per million children.

90 percent of the children who died hadn’t been fully vaccinated.

Viral Strains and Vaccine Effectiveness

Last season saw two influenza A strains circulating at nearly equal levels. Among subtyped viruses, 53.1 percent were A(H1N1)pdm09 and 46.9 percent were A(H3N2). Most years one strain dominates.

The A(H3N2) viruses proved particularly problematic for older adults. People 65 and older experienced a hospitalization rate of 407.6 per 100,000—more than eight times higher than adults aged 18-49. They represented 57 percent of all hospitalizations despite being only 17 percent of the population.

Among children and adolescents, the vaccine was 32-60 percent effective in outpatient settings and 63-78 percent effective against hospitalization. For adults, effectiveness ranged from 36-54 percent in outpatient settings and 41-55 percent against hospitalization.

Vaccinated people had roughly 50 percent lower risk than unvaccinated people in the same circumstances. The vaccine worked substantially better at preventing hospitalization.

A(H3N2) viruses have historically shown lower vaccine effectiveness than other flu strains. The virus mutates faster. When predictions about which variant will circulate are even slightly off, effectiveness drops.

Hospital System Strain

When hospitals designed to operate at 85 percent capacity suddenly hit 120 percent, the system breaks in specific ways.

Emergency departments fill first. When every bed is occupied and ambulances keep arriving, patients wait in hallways. Some hospitals reported ED wait times exceeding eight hours, compared to typical two-hour waits during normal periods.

Operating rooms convert to overflow spaces. OR nurses get reassigned to medical floors. Elective surgeries get postponed. A hip replacement might be elective, but the 70-year-old who’s been waiting six months and can barely walk isn’t experiencing it as optional.

The CDC recommends that healthcare personnel with flu stay home for at least 24 hours after fever resolves without medication. This removes skilled workers when patient demand peaks, forcing remaining staff to cover more patients and work longer hours—conditions that increase their infection risk.

Someone having a heart attack during peak flu season faces longer waits for ECG interpretation, delayed cardiac catheterization, and potentially worse outcomes because the emergency department is overwhelmed with respiratory illness. A patient needing emergency surgery might get transferred to a hospital 50 miles away because the local facility has no ICU beds available.

During the 2024-2025 season, flu deaths exceeded COVID-19 deaths for the first time since the pandemic began, with influenza accounting for 2.8 percent of all deaths during the peak week in February 2025.

2025-2026 Season Trajectory

The 2025-2026 season started earlier and accelerated faster than typical years. By week 50 of 2025 (mid-December), the cumulative hospitalization rate stood at 11 per 100,000 population—the third-highest rate at this point in any season since 2010.

A(H3N2) viruses dominate this season, specifically a subclade designated as K (or J.2.4.1 in technical nomenclature). This variant has shown rapid global expansion, detected in more than 34 countries over the past six months. In the Western Pacific Region, subclade K viruses represented 89 percent of sequences submitted to the global tracking database as of late November 2025.

The subclade K viruses have genetically drifted from related strains with several amino acid changes in their hemagglutinin protein—the surface antigen that vaccines target and antibodies recognize. Early vaccine effectiveness estimates from the WHO suggest the current vaccine is 70-75 percent effective at preventing hospital attendance in children aged 2-17 and 30-40 percent effective in adults.

The difference between 30 percent protection and no protection is the difference between some people staying out of overwhelmed hospitals and more people flooding them.

Colorado’s experience provides a window into what’s happening nationally. The state hit a hospitalization rate of 40 per 100,000 population in late December 2025—a threshold it didn’t reach until late January during the previous season. That’s four weeks earlier. If other states follow similar trajectories, we’re looking at a longer, more intense season than last year.

High-Risk Groups

Adults 65 and older face the starkest risk. Last season they accounted for 57 percent of hospitalizations. Their hospitalization rate reached 407.6 per 100,000—more than eight times higher than adults aged 18-49.

Young children, particularly those under 2, face elevated risk. Their immune systems haven’t encountered flu viruses before. Children aged 0-4 experienced a cumulative hospitalization rate of 104.7 per 100,000 last season. Infants under 6 months face the worst odds—they’re too young to receive the flu vaccine and depend entirely on caregivers being vaccinated.

Pregnancy alters immune response, reduces lung capacity, and increases metabolic demands. The CDC recommends that pregnant women receive flu vaccination during any trimester and that healthcare providers offer antiviral treatment to pregnant women who develop flu symptoms.

People with chronic medical conditions—asthma, COPD, heart disease, diabetes, kidney disease, liver disease, neurologic disorders, compromised immune systems, obesity—all face elevated risk. 89 percent of hospitalized patients last season had at least one underlying medical condition.

This includes well-controlled asthma, diabetes managed with medication, or hypertension treated with pills—conditions that still elevate flu risk enough to change the treatment calculus.

CDC Recommendations for 2025-2026

Everyone 6 months and older should get vaccinated, ideally by the end of October but continuing throughout the season.

The 2025-2026 vaccine formulation changed based on circulating strains observed last season. It’s a trivalent vaccine protecting against three viruses: an A(H1N1)pdm09-like virus, an A(H3N2)-like virus, and a B/Victoria lineage virus. The A(H3N2) component specifically changed from last year based on CDC assessment of current strain characteristics.

Adults 65 and older have additional options: high-dose vaccines, recombinant vaccines, or adjuvanted vaccines that provide enhanced immune response in older adults who typically show weaker responses to standard-dose vaccines.

FluMist, the nasal spray vaccine, is now approved for self-administration. People aged 18-49 can administer it to themselves. Caregivers 18 and older can give it to children aged 2-17 who meet eligibility criteria. Previously, FluMist could only be given by healthcare providers in clinical settings.

Antiviral Treatment Access

Four FDA-approved antivirals exist: oseltamivir (Tamiflu), inhaled zanamivir (Relenza), intravenous peramivir (Rapivab), and oral baloxavir (Xofluza). All require prescriptions. All work best when started within 1-2 days of symptom onset.

The CDC says antivirals should be started as soon as possible for hospitalized patients without waiting for test confirmation. For outpatients at high risk or with severe illness, treatment should start if initiated within 48 hours of symptom onset.

You develop flu symptoms on a Friday evening in January. Your primary care doctor is booked solid for three weeks. Urgent care centers have two-hour waits. You could go to the emergency department, but you’ve heard they’re overwhelmed. You could try telehealth, assuming you have insurance that covers it and can find an available appointment within 48 hours.

If you’re uninsured, the situation gets worse.

Research from the 2023-2024 season found that only slightly more than half of high-risk adults diagnosed with flu in emergency departments and urgent care centers received antiviral prescriptions. Of those who got prescriptions, only 80 percent filled them. High-risk adults 65 and older were less likely to receive prescriptions or fill them compared to younger high-risk adults—despite facing the greatest risk of complications.

Patients who underwent rapid flu testing in emergency departments or urgent care centers were more likely to be prescribed and dispensed antivirals. Without rapid test results, clinicians hesitate to prescribe based on clinical suspicion alone.

Throughout the 2024-2025 season, multiple oseltamivir formulations experienced periodic unavailability at different manufacturers. When national demand spikes during peak season, manufacturing capacity constraints become apparent. Some regional pharmacies reported stock-outs of preferred formulations, forcing patients to accept less convenient dosing or intravenous administration when oral medication was preferred.

When to Seek Medical Care

The CDC recommends that people at high risk seek prompt medical evaluation upon symptom onset rather than waiting to see whether symptoms improve. If you’re 65 or older, pregnant, have chronic medical conditions, or care for young children, call your doctor’s office when symptoms start.

Testing should be considered when flu viruses are circulating in your community, you have symptoms consistent with flu, and the result will change clinical management. Testing makes sense when it will lead to antiviral treatment.

Rapid molecular assays are preferred over rapid antigen tests. Molecular assays detect viral nucleic acids with 90-95 percent sensitivity, while rapid antigen tests only achieve 50-80 percent sensitivity. Many rapid molecular assays are CLIA-waived, meaning they can be performed in any outpatient setting without requiring reference laboratory processing.

For otherwise healthy people without high-risk conditions, staying home and managing symptoms with rest, fluids, and fever-reducing medications remains appropriate for mild illness. If you develop warning signs—difficulty breathing, chest pain, severe muscle pain, dehydration, confusion, or symptoms that improve then suddenly worsen—seek medical care regardless of risk status.

Tracking Local Flu Activity

Flu activity varies dramatically by region and timing.

The CDC’s FluView Interactive platform displays national, regional, and state-level data. You can examine laboratory data, medically attended visits for flu-like illness, hospitalization rates by region, and mortality data. During high-activity periods, checking this weekly provides clear pictures of trends in your area.

State health departments maintain their own surveillance dashboards. Colorado’s Department of Public Health and Environment provides daily updates on flu hospitalizations, test positivity rates, and wastewater surveillance data tracking viral shedding across the state.

The CDC now provides wastewater monitoring data tracking influenza A detection across different regions. These data can signal that infections are increasing in a community before case numbers peak, though interpretation requires caution since wastewater reflects community-wide transmission without providing information about severity.

During the 2024-2025 season, western regions peaked in late December while eastern regions peaked in early February—a month-long span of peak activity across different geographies.

Protective Measures

Vaccination remains the single most effective intervention. Even with 30-50 percent effectiveness against infection, vaccines dramatically reduce hospitalization risk. Last season, vaccinated children were 63-78 percent less likely to require hospitalization if they caught flu.

The earlier you get vaccinated, the better. While the CDC no longer recommends July and August vaccination for most adults, vaccination during September and October provides optimal protection throughout the season. For adults 65 and older, the CDC recommends avoiding July and August vaccination unless a subsequent opportunity in September or October is unlikely.

Antiviral treatment works, but only if you can access it quickly. If you’re in a high-risk group and develop symptoms, call your healthcare provider immediately. If you can’t reach them, consider urgent care or telehealth. The 48-hour window matters.

For post-exposure prophylaxis, baloxavir (Xofluza) is now approved for household contacts of confirmed flu cases. If someone in your household gets diagnosed with flu and you’re at high risk, a single dose of baloxavir within 48 hours of exposure can prevent infection.

Basic precautions during high-activity periods include washing hands frequently, avoiding touching your face, staying home when sick, and considering masking in crowded indoor spaces when community transmission is high.

Community Impact of Individual Decisions

Hospitals operate with razor-thin surge capacity in normal times. When demand exceeds normal levels by 50 or 100 percent, cascading failures result: emergency departments overflow, elective surgeries get postponed, critically ill patients with non-flu conditions face delayed care, and healthcare workers fall ill in large numbers.

Your vaccination decision carries implications beyond personal health. It affects whether your community’s emergency department can care for your neighbor’s heart attack, whether ambulances can reach you within reasonable timeframes, and whether pediatric intensive care units have capacity for the sickest children.

During the 2024-2025 season, 90 percent of children who died from flu hadn’t been fully vaccinated. Most had no underlying medical conditions—they were otherwise healthy kids.

The 2025-2026 season is already tracking toward similar or worse severity. Hospitalization rates in mid-December 2025 matched levels not reached until mid-January during the previous season. Colorado reported record-breaking weekly hospitalizations in late December. The dominant A(H3N2) subclade K variant has spread to 34 countries and shows genetic drift from vaccine strains.

The CDC’s guidance for this season urges a both-and approach: vaccinate everyone who can receive vaccine safely, while simultaneously ensuring that those at highest risk understand when to seek medical evaluation and how to access antiviral treatment.

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