[Edaily Reporter Jang Yeong-Rak ] The influenza (flu) season, which began in early September—a month earlier than usual—had temporarily slowed down but has now resumed its upward trend. The medical community has recommended that high-risk groups get vaccinated, as it can prevent the disease from progressing to a severe stage.

According to the Korea Disease Control and Prevention Agency’s (KDCA) infectious disease sentinel surveillance on the 7th, the rate of suspected influenza cases in Week 44 (October 25–31) was 22.8 per 1,000 outpatient visits, an increase of 3.6 from the previous week (19.2).
Over the past four weeks, the rate of suspected cases has been 21.6, 17.7, 19.2, and 22.8 per 1,000 outpatients, respectively, marking two consecutive weeks of week-over-week increases, indicating that the influenza outbreak is gaining strength again. The threshold for issuing an influenza outbreak advisory this season is 12.9 cases. This year’s influenza epidemic alert was issued two months earlier than last year.
The Korea Disease Control and Prevention Agency (KDCA) anticipates that the outbreak could persist for an extended period until next spring.
The medical community notes that while people who have already contracted the flu or have recently recovered may feel less need for the flu vaccine, they recommend considering vaccination as soon as possible—or at the very latest—since multiple subtypes of the influenza virus exist and reinfection is possible.
It takes about two weeks for antibodies to develop after receiving the flu vaccine. Since the flu in Korea typically follows a pattern of a first wave from December to January of the following year, followed by a second wave in March and April, getting vaccinated in late November or early December is still expected to be fully effective.
Furthermore, since the flu vaccine is highly effective not only in preventing infection itself but also in reducing severe complications among high-risk groups, it helps lower the risk of developing severe conditions—such as pneumonia or hospitalization—during the remainder of the flu season.
Therefore, even if the flu season has already begun, it is unlikely that it is too late to get vaccinated; in particular, high-risk groups are advised to complete their vaccinations by early December.
High-risk groups—including seniors aged 65 and older, people with chronic conditions such as heart disease, lung disease, and diabetes, pregnant women, infants and young children, immunocompromised individuals, and workers in medical institutions and long-term care facilities—are advised to get the flu vaccine every year.
The flu vaccine used in Korea this year is a trivalent vaccine that includes two types of influenza A (H1N1 and H3N2) and the Victoria lineage of influenza B. The Yamagata lineage of influenza B, which was previously included in the quadrivalent vaccine, has not been detected worldwide since March 2020 and has been excluded starting this year in accordance with World Health Organization (WHO) recommendations. The trivalent and quadrivalent vaccines offer equivalent efficacy and safety and are optimized for the viruses currently circulating.