Dr Harold Mandel Daily Rounds

Influenza, shortened to flu, is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to hospitalization or death. Understanding what drives flu and how to reduce your risk remains central to staying healthy this season.

In this article 1:What Causes Flu 2:How It Spreads 3:Prevention That Works 4:2025-2026 Season: What's New 5:Treatment and When to Seek Care

What Causes Flu

Flu is caused by influenza viruses, which are divided into four types: A, B, C, and D. Human seasonal epidemics are driven by influenza A and B.

• Influenza A: The most common cause of seasonal flu and the only type known to cause pandemics. It is subtyped by surface proteins hemagglutinin (H) and neuraminidase (N), such as H1N1 and H3N2.
• Influenza B: Circulates seasonally and can cause outbreaks, typically with two lineages. It is not divided into subtypes.
• Influenza C: Usually causes mild illness and does not drive seasonal epidemics.
• Influenza D: Primarily affects cattle and is not known to infect people.

These viruses evolve constantly through antigenic drift, small genetic changes, and occasionally antigenic shift, a major change, which is why updated vaccines are needed each year.

How It Spreads

Flu spreads mainly from person to person through respiratory droplets when people cough, sneeze, or talk. Less commonly, it can spread by touching a surface with flu virus on it and then touching your mouth, nose, or eyes.

Close contact Within about 6 feet of someone who is sick Peak contagiousness 1 day before symptoms through 5 to 7 days after onset Incubation Typically 1 to 4 days, average 2 days

People may be infectious before they know they are sick, which makes prevention measures especially important during community spread.

Prevention That Works

The most effective way to reduce flu risk is layered prevention. No single measure is perfect, but together they lower infection and severe disease.

💉Get vaccinated every year Annual flu vaccine is recommended for everyone 6 months and older, ideally by the end of October. Vaccination reduces illness, medical visits, and hospitalizations.🧼Practice hand hygiene Wash hands with soap for 20 seconds, use alcohol-based sanitizer when soap is not available, and avoid touching your face.😷Use respiratory etiquette Cover coughs and sneezes with a tissue or elbow, stay home when sick, and consider masking in crowded indoor settings when flu activity is high.🌬️Improve ventilation Open windows when possible, use air filtration, and avoid close contact in poorly ventilated spaces.🧽Clean high-touch surfaces Regular cleaning of doorknobs, phones, and shared equipment helps reduce indirect transmission. 

Special Recommendation: Adults 65 and Older

Adults 65 years and older should receive a higher-dose or adjuvanted flu vaccine when available, such as high-dose inactivated, adjuvanted inactivated, or recombinant formulations. These vaccines are designed to create a stronger immune response in older adults.

CDC recommends that people 65+ get vaccinated early in the season and talk to their clinician about which formulation is appropriate. If a preferred higher-dose option is not available, getting any age-appropriate vaccine is better than remaining unvaccinated.

2025-2026 Season: What's New

CDC Update Season 2025-2026

• •Thimerosal-free formulations expanded: All U.S. flu vaccines for 2025-2026 are thimerosal-free or contain only trace thimerosal, reflecting continued transition to preservative-free single-dose presentations.
• •FluMist self-administration option: For the first time, eligible adults 18 to 49 can self-administer FluMist nasal spray at home after an online screening and pharmacy fulfillment, while caregivers can administer to children 2 to 17. This follows FDA approval for at-home use.
• •Trivalent composition: Vaccines continue as trivalent, covering two influenza A strains and one influenza B/Victoria strain, as B/Yamagata has not circulated since 2020.
• •Timing remains key: CDC advises vaccination in September or October for most people, though vaccination should continue as long as flu circulates.

Note: Availability of self-administered FluMist may vary by state pharmacy regulations and insurance coverage. Check with your pharmacy for eligibility and ordering steps.

Treatment and When to Seek Care

Most people with flu recover in a few days to less than two weeks, but some people develop complications such as pneumonia, bronchitis, or worsening of chronic conditions.

Rx Antiviral treatment Prescription antivirals like oseltamivir and baloxavir work best when started within 48 hours of symptoms. They are especially important for people at higher risk: adults 65+, young children, pregnant people, and those with asthma, diabetes, heart disease, or weakened immunity.⚠ Seek care promptly if you have

• • Difficulty breathing, shortness of breath, or chest pain
• • Persistent fever, dizziness, confusion, or severe vomiting
• • Symptoms that improve then return with fever and worse cough
• • For children: fast breathing, bluish lips, not drinking enough fluids, or not interacting normally

This information is educational and does not replace professional medical advice. If you are unsure whether you need testing or treatment, contact your clinician or urgent care promptly. Sources & Further Reading↗CDC: 2025-2026 Flu Season Overview — cdc.gov/flu/season/2025-2026.html↗CDC: Flu Prevention — cdc.gov/flu/prevention/ Dr. Harold Mandel Publisher, MandelNews.com • Daily Rounds

Dr. Harold Mandel is a medical journalist and author covering infectious disease, prevention, and public health policy. Daily Rounds distills current CDC guidance into practical, reader-friendly updates.