Key points
- Korea's 2026–27 influenza advisory was issued on September 11, 2026, more than a month earlier than last season (October 17).
- Flu typically starts suddenly, with a fever of 38°C (100.4°F) or higher and aching all over, but it cannot be told apart from COVID-19 by symptoms alone.
- Flu antivirals work best when started within 48 hours of symptoms. If you are over 65 and develop a fever, it is best to see a doctor promptly.
Why did flu season start so early in 2026?
The Korea Disease Control and Prevention Agency (KDCA) issued its 2026–27 influenza advisory at midnight on September 11, 2026. At that point, clinics were seeing 25.3 flu-like illness cases per 1,000 outpatient visits, almost double this season's threshold of 12.9 and 3.8 times the figure a year earlier (6.6). The previous two advisories came on October 17, 2025 and December 20, 2024.
The main circulating strain is influenza A(H1N1)pdm09. KDCA says it closely matches this season's vaccine strain and shows no mutations linked to antiviral resistance.
Where things stand in early November
Flu-like illness fell for three weeks, from 33.0 per 1,000 in week 39 to 17.7 in week 42, then rose again to 19.2 in week 43 (October 18–24). Children aged 7–12 had the highest rate (49 per 1,000), and the rate among people 65 and older rose from 5.9 to 7.3. Hospital admissions for flu (380 that week) were down from the week before but about four times the level a year earlier (98). KDCA expects the epidemic could last through winter into spring.
| Week (2026) | Flu-like illness at clinics (per 1,000 outpatients) |
|---|---|
| Advisory issued (Sept 11) | 25.3 (threshold 12.9) |
| Week 39 | 33.0 |
| Week 40 | 23.6 |
| Week 41 | 21.6 |
| Week 42 | 17.7 |
| Week 43 (Oct 18–24) | 19.2 (first rise in four weeks) |
COVID-19 hospitalizations have been rising at the same time, from 248 in week 39 to 283 in week 40 in KDCA's sentinel surveillance, and about 63% of those hospitalized with COVID-19 were 65 or older. That is why health authorities are warning about a "twindemic."
Flu vs. COVID-19 vs. the common cold
All three can cause a cough, sore throat and fatigue. The biggest differences are how fast symptoms start and how strong the whole-body symptoms are.
| Flu (influenza) | COVID-19 | Common cold | |
|---|---|---|---|
| Onset | Sudden, within hours | Gradual or sudden; varies | Gradual |
| Fever | High fever (38°C+) and chills are common | May or may not occur | None or low-grade |
| Body aches, headache | Often severe | Common | Mild |
| Runny nose, sneezing | Possible | Possible | Most prominent |
| Change in smell or taste | Rare | Possible, though reported less often with recent variants | Briefly, from congestion |
| Incubation | Usually 1–4 days | Usually 2–5 days (up to 14) | 1–3 days |
| Treatment | Antivirals available | Oral antivirals for high-risk patients | Symptom relief |
The U.S. CDC also notes that flu and COVID-19 cannot be distinguished by symptoms alone; testing is needed, and people can have both at once. If you have a fever and feel badly run down, getting tested is a better choice than assuming it is "just a cold."
Flu self-check
If several of these apply, flu is possible. This does not replace a diagnosis.
- A fever of 38°C or higher came on suddenly within half a day, with chills.
- Your muscles and joints ache all over, and you have a headache.
- You feel too weak to get out of bed.
- You also have a dry cough or a sore throat.
- Someone at home, a grandchild, or a coworker recently had the flu.
When should flu antivirals be taken?
Flu antivirals stop the virus from multiplying, so they work best when started within 48 hours of symptom onset. Options used in Korea include oral oseltamivir (e.g., Tamiflu), single-dose baloxavir, intravenous peramivir and inhaled zanamivir. Your doctor will choose based on your age, kidney function and other medicines.
The CDC recommends that people at high risk of complications, such as those 65 and older, and anyone sick enough to be hospitalized, start antivirals as soon as possible even after 48 hours. During an advisory period, KDCA has also allowed high-risk patients, including those 65 and older, with suspected flu to receive antivirals covered by national health insurance without waiting for a test result.
- Antibiotics do not work against the flu virus. They are used only for complications such as bacterial pneumonia.
- Rare cases of sudden abnormal behavior (such as jumping or hallucinations) have been reported in children and teens after taking flu antivirals, so Korea's Ministry of Food and Drug Safety advises not leaving a child alone for at least two days after starting treatment. Such behavior can also be caused by the flu itself. This is worth remembering if you look after grandchildren.
Why people over 65 need to be more careful
For younger adults, flu usually means a few miserable days. With age, it more often leads to pneumonia or a flare-up of existing conditions. When this season's advisory was issued, about 60% of people hospitalized with flu were 65 or older.
Flu also strains the heart. In a study from Ontario, Canada (Kwong et al., NEJM 2018), the risk of heart attack was about six times higher in the seven days after laboratory-confirmed flu. If you have heart disease, diabetes or chronic lung disease, it is best to see a doctor as soon as flu symptoms start.
Seek emergency or urgent care if
- You are short of breath or have trouble breathing, or have ongoing chest pain or pressure
- You feel confused, or too dizzy to stand
- You can barely drink and are urinating much less than usual
- Fever and cough seem to improve and then come back worse (a possible sign of pneumonia)
- A chronic condition such as heart disease, diabetes or lung disease suddenly gets worse
Recovering at home
- Fluids and rest: Fever drains your body's water. Sip water or barley tea often.
- Stick to the labeled dose of fever reducers: Cold and flu remedies often contain the same ingredient (such as acetaminophen/paracetamol), so check the boxes to avoid doubling up.
- Protect others: Avoid crowds for about a day after your fever is gone, cough into your sleeve and wash your hands often. KDCA advises that children with flu stay home from daycare or school until 24 hours after their fever has gone without fever reducers.
- Vaccination: If you have not been vaccinated yet, it is still worth doing. See Korea's free 2026–27 flu and COVID-19 vaccines for 65+ for dates.
Flu myths: true or false?
| Myth | What the evidence says |
|---|---|
| The flu shot gives you the flu | Injected flu vaccines do not contain live virus and cannot cause the flu. A day or two of low fever or aches can occur and usually passes on its own. |
| If I had a shot last year, I don't need one this year | Circulating strains change each year and vaccine protection fades, so a shot every year is recommended. |
| I already had flu this season, so I can't get it again | You can catch a different type (for example, influenza B after influenza A). Vaccination is still recommended. |
| Flu is just a bad cold | It is caused by a different virus, and in older adults it often leads to complications such as pneumonia and heart attack, and to hospitalization. That is why it has its own vaccines and antivirals. |
Please keep in mind
- This article is based on information checked as of the date shown above. New research or changes in official guidance may change the content, so please use it as a reference rather than as definitive advice.
- For an accurate diagnosis and advice about your own health, please see a doctor in person.