Health organizations raise warnings about this year’s flu, recommend vaccine for most

Editor’s note: “Behind the News” is the product of Sun staff assisted by the Sun’s AI lab, which includes a variety of tools such as Anthropic’s Claude, Perplexity AI, Google Gemini and ChatGPT.

 

A fast-spreading H3N2 flu strain is driving an unusually intense early season in the U.S., with millions of illnesses and higher-than-normal hospitalizations heading into the holidays. Flu and COVID-19 are both surging in many areas, but they remain distinct infections with different risk profiles, symptom patterns and vaccines.

The new strain and why it is bad

Most lab-confirmed flu in the U.S. this season is influenza A, dominated by an H3N2 strain in a newer subclade that appears especially good at spreading and making people fairly sick. H3N2 seasons historically hit older adults and young children harder, with more hospitalizations and complications than many H1N1 or influenza B-dominant years. [1]

This year’s circulating H3N2 viruses are antigenically related to the strains included in the current vaccine, but not a perfect match, which may blunt protection against infection while still helping prevent severe disease, hospitalization and death. [2]

How this season compares

The Centers for Disease Control and Prevention estimates at least 4.6 million illnesses, 49,000 hospitalizations and 1,900 deaths so far this season in the U.S., including at least one pediatric death, as of Dec. 13. [3]

The current cumulative flu hospitalization rate (about 11 per 100,000) is the third-highest for this week in the past 15 years, behind only 2022-23 and 2023-24. [4]

Last season (2024-25) was classified by CDC as “high severity,” with activity higher than most pre-COVID seasons; this year is tracking as another early, strong season rather than a mild one. [5]

Midseason data this year show cumulative hospitalization rates already tracking above typical seasons and approaching the trajectory seen early in 2024-25, but not yet at that record final level. In 2024-25, the U.S. ended with a cumulative flu hospitalization rate of about 127 per 100,000 people, the highest recorded since at least 2010-11, and roughly 1.8 to 2.8 times the median since the 2010-11 season. [6, 7]

Deaths from flu are clearly higher than in mild seasons, but current weekly death proportions remain below the peak weeks of the worst recent years, when flu accounted for several percent of all U.S. deaths. [8]

Past “severe” seasons like 2017-18 and 2024-25 were defined mainly by how many people got seriously ill, not by flu suddenly becoming deadlier on a per-patient basis. This year’s H3N2-heavy season appears similar so far: clinical severity in hospitalized patients looks comparable to past years, but elevated transmission is driving more hospital beds and, inevitably, more deaths than in an average flu year. [9]

Symptoms and when to suspect flu

This year’s flu usually comes on abruptly over hours, not days. Typical symptoms include: [10] fever or feeling feverish/chills, dry cough and sore throat, runny or stuffy nose, body and muscle aches, headache and marked fatigue. Sometimes vomiting or diarrhea occurs, more common in children.

Red flags that warrant urgent care include trouble breathing, chest pain, confusion, persistent high fever, dehydration or in children, fast breathing, bluish lips/face or inability to drink or wake up normally.[10]

Prevention and flu shot numbers

Key preventive steps this season:

• Get vaccinated: Everyone 6 months and older is recommended to receive an annual flu shot, which reduces risk of severe illness, hospitalization and death even when it does not fully prevent infection. [4]
• Use masks and stay home when sick: Especially in crowded indoor spaces, masking lowers spread of both flu and COVID-19; staying home while symptomatic limits outbreaks in schools and workplaces.[11]
• Improve ventilation and hand hygiene: Opening windows, using air filters and regular handwashing help cut transmission of respiratory viruses.[23]

More than 121 million flu vaccine doses have been distributed in the U.S. this season, with CDC and experts urging those not yet vaccinated to get a shot as activity climbs. [24]

Vaccine effectiveness

Early data suggest this season’s flu vaccine offers moderate protection against the new H3N2 “subclade K” strain — stronger at preventing severe illness and hospital visits than preventing all infections, and generally more important for high-risk groups, including children, elderly, pregnant women and those with underlying conditions. In plain terms, the shot is not a perfect match but still meaningfully cuts the risk of getting very sick. [12]

According to a U.K. analysis, this year’s vaccine is estimated to cut H3N2 cases that are bad enough to need a doctor visit by roughly 32% to 39% in adults. [13]

In children and adolescents, early estimates are much higher — around 72% to 75% — effectiveness against severe influenza from this H3N2 strain. [14]

In typical modern flu seasons, overall effectiveness often lands between about 30% and 60%, depending on age and strain. [15]

Scientists say the new H3N2 subclade has mutated enough that the vaccine is not an ideal antigenic match, which likely lowers protection against mild or any infection.[12]

Flu vs. COVID-19

Flu and COVID-19 overlap but differ in important ways: [16]

• Virus type: Seasonal flu is an influenza A virus, while COVID-19 is a SARS-CoV-2 coronavirus.
• Onset of symptoms: Flu is abrupt, within hours to one to three days after exposure. COVID-19 takes about 2-14 days after exposure, sometimes more gradual.[25]
• Typical symptoms: Both share similar symptoms, including high fever, body aches, dry cough, sore throat and fatigue. COVID-19 symptoms additionally can include loss of smell, red swollen eyes and skin rashes.[25]
• Long-term effects: Postviral fatigue is possible with flu, but long-term sequelae are less common. Long COVID (persistent fatigue, brain fog, breathing issues) is more common.[25]

National wastewater SARS-CoV-2 levels are at moderate but rising levels in many regions, and recent data show clear increases across most metrics through early December, although hospitalizations and deaths remain well below prior major surges. Emergency department visits and hospitalizations are highest among young children and seniors, but less than 1% of recent U.S. deaths are currently attributed to COVID-19. [16]

Treatment recommendations

Recommended treatment for suspected flu this season still centers on early use of antivirals in the right patients plus supportive care (rest, fluids, fever control). The big emphasis from clinicians and public-health groups is: If you are high-risk or very sick, get evaluated quickly so treatment can start within the first 48 hours of symptoms. [17]

Who should get antivirals

Current guidance recommends prompt antiviral treatment (without waiting for test results) for people with suspected flu who: [18]

• are hospitalized or have severe/progressive illness (trouble breathing, chest pain, confusion, dehydration)
• are at higher risk of complications: adults 65 and older, children under 2, pregnant or recently postpartum people, residents of nursing homes, or those with chronic conditions (heart, lung, diabetes, kidney, neurologic, immunocompromising conditions).

For otherwise healthy people with mild illness, clinicians may still prescribe antivirals (especially if seen within 48 hours), but treatment is more strongly prioritized for the groups above.

Which medications are used

Four FDA-approved antivirals are in routine use for flu this season: [19]

• Oseltamivir (Tamiflu, generic): oral capsules or liquid; standard first-line option for most ages, including pregnant people and young children.
• Zanamivir (Relenza): inhaled powder; for people 7 and older but not recommended in asthma, chronic obstructive pulmonary disease or other chronic lung disease because it can worsen breathing. [18]
• Baloxavir marboxil (Xofluza): single-dose oral drug for early, uncomplicated flu in certain age groups; not used in pregnancy, breastfeeding, hospitalized patients or those with complicated disease. [20]
• Peramivir (Rapivab): single-dose intravenous drug, mainly for hospitalized patients who cannot take oral medications. [17]

These medicines work best when started within one to two days of symptom onset, shortening illness by about a day and lowering the risk of complications like pneumonia and hospitalization; starting later can still help if the patient is high-risk or already hospitalized. [19]

Home care and what not to do

For most otherwise healthy people, home management plus monitoring is appropriate: [21]

Rest, plenty of fluids and light food as tolerated. Acetaminophen or ibuprofen for fever and aches (no aspirin for children due to Reye’s syndrome risk). Over-the-counter cough suppressants, decongestants or throat lozenges as needed, following age and dosing instructions.

Antibiotics do not treat flu itself and are only used if a bacterial complication (like sinusitis, ear infection or pneumonia) is diagnosed. [22]

When to seek urgent or emergency care

People with suspected flu should seek urgent or emergency care for: [22]

• difficulty breathing, chest pain or bluish lips/face
• new confusion, seizures or inability to wake or stay awake
• persistent high fever, severe weakness or signs of dehydration (no urination, dizziness, dry mouth, in children no tears when crying)
• in children: fast or labored breathing, ribs pulling in with each breath, not drinking or fewer wet diapers.

 

Sources

[1] https://www.nbcnews.com/health/health-news/flu-season-states-severity-new-variant-k-vaccines-kids-rcna250056l

[2] https://www.cdc.gov/fluview/surveillance/2025-week-48.html

[3] https://www.cdc.gov/fluview/surveillance/2025-week-50.html

[4] https://flutrackers.com/forum/forum/united-states/seasonal-flu-2009-2014-including-h1n1-pandemic-2009-aj/1023331-us-fluview-weekly-surveillance-flu-report-2025-2026-season-for-trend-analysis

[5] https://theamericannews.com/cdcs-early-flu-season-warning-2025-what-it-means-for-american-households/

[6] https://www.cidrap.umn.edu/influenza-general/us-data-highlight-severity-2024-25-flu-season

[7] https://www.ajmc.com/view/us-flu-hospitalizations-reach-highest-levels-in-over-a-decade

[8] https://www.beckershospitalreview.com/quality/public-health/how-flu-deaths-compare-to-past-seasons/

[9] https://www.cdc.gov/mmwr/volumes/74/wr/mm7434a1.htm

[10] https://www.cbsnews.com/news/flu-season-2025-experts-pretty-worried/

[11] https://www.cdc.gov/respiratory-viruses/prevention/masks.html

[12] https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON586

[13] https://news.northeastern.edu/2025/12/22/difficult-super-flu-season/

[14] https://www.gavi.org/vaccineswork/superflu-or-same-old-flu-how-subclade-k-influenza-playing-out-worldwide

[15] https://publichealth.jhu.edu/2025/virus-transmission-trends-winter-2025-26

[16] https://thesicktimes.org/2025/12/16/national-covid-19-trends-december-16/

[17] https://www.nfid.org/resource/influenza-flu-treatment/

[18] https://www.cdc.gov/flu/treatment/antiviral-drugs.html

[19] https://www.lung.org/lung-health-diseases/lung-disease-lookup/influenza/diagnosing-and-treating-influenza

[20] https://www.mayoclinic.org/diseases-conditions/flu/diagnosis-treatment/drc-20351725

[21] https://www.healthline.com/health/flu-treatments

[22] https://www.lung.org/lung-health-diseases/lung-disease-lookup/pneumonia/treatment-and-recovery/bacterial

[23] https://share.upmc.com/2025/11/prevent-respiratory-illnesses-ventilation/

[24] https://www.cdc.gov/fluvaxview/dashboard/index.html

[25] https://www.nyp.org/medicalgroups/westchester/for-patients/healthcare-articles/covid-19-vs-flu#:~:text=Other%20symptoms%20of%20COVID%2D19%20include:%20*%20Red%2C,stay%20awake%20*%20Bluish%20lips%20or%20face