Influenza is spreading faster and earlier than in previous years in South Korea, with cases rising among elementary school students since the new school term began. Health authorities say a high fever or cough should not be dismissed as a common cold and warrants proper testing.
The number of suspected influenza cases stood at 31.0 per 1,000 outpatients at clinic-level medical institutions in the 37th week of the year, or Sept. 7 to 13, the Korea Disease Control and Prevention Agency said on the 17th. That is 3.4 times the 9.2 recorded in the 34th week, after 13.3 in the 35th week and 25.3 in the 36th week. Hospitalizations are also climbing quickly. Flu inpatients at hospital-level institutions rose 4.7-fold to 417 in the 37th week from 89 in the 34th week. At tertiary general hospitals, inpatients jumped more than ninefold to 73 from eight over the same period.
COVID-19 hospitalizations are rising as well. Inpatients at hospital-level institutions increased to 287 in the 37th week from 61 in the 34th week, after 115 in the 35th week and 196 in the 36th week, a gain of about 4.7 times in four weeks. At tertiary general hospitals, however, the increase was modest, at 16 in the 37th week from 13 in the 34th week.
Influenza and COVID-19 share symptoms such as fever, cough and sore throat, making them difficult to tell apart on symptoms alone. Influenza tends to bring on a high fever more abruptly than a common cold, often accompanied by headache, chills, muscle pain and general weakness. COVID-19 can also cause fever, cough and sore throat, and some patients develop a loss of smell or taste, or difficulty breathing.
If influenza is suspected, testing and treatment should not be delayed. A rapid antigen test returns results in about 15 minutes but is relatively less sensitive. If the result is negative despite clear symptoms, doctors may order additional tests, such as molecular testing.
Antiviral drugs are known to be most effective when given within 48 hours of symptom onset. Tamiflu, Peramiflu and baloxavir are among the commonly used options. For high-risk groups prone to complications — older adults, people with chronic conditions, pregnant women and infants — treatment may still begin after 48 hours at a doctor's discretion.
Left untreated, influenza can progress to pneumonia. Beyond pneumonia caused by the virus itself, bacterial pneumonia can set in after the flu weakens the immune system. Other complications include myositis, myocarditis, pericarditis and encephalitis.
Patients should seek medical care if a high fever persists for three to four days or more, if fever does not subside despite fever-reducing medication, or if they develop difficulty breathing, chest pain or a bluish discoloration of the skin. For high-risk groups, including older adults and people with chronic conditions, early treatment is safer even when symptoms are mild.
Vaccination also matters. The national influenza immunization program for the 2026-2027 season begins on the 21st, rolling out by eligibility group. Flu and COVID-19 vaccines can be given at the same time.
"Influenza, COVID-19 and the common cold cannot be perfectly distinguished by symptoms alone, so getting tested immediately when you suspect infection is the most accurate approach," said Park Wan-beom, a professor of infectious diseases at Seoul National University Hospital. "High-risk groups such as older adults and people with underlying conditions should not put off vaccination, and everyone should stick closely to basic precautions like wearing masks and practicing hand hygiene."
