Following the subsiding of the Covid-19 pandemic and a return to normalcy, influenza cases in Korea witnessed a remarkable surge of over 9,000 percent from 2021 to 2022. Yet, over the past four years, there has been a consistent annual decrease in the number of flu cases, averaging 25 percent.

The National Health Insurance Service (NHIS) reported on the health insurance treatment status of influenza patients from 2018 to 2022, utilizing health insurance treatment data. The count of treated flu patients rose substantially, escalating from 9,574 in 2021 to 873,590 in 2022, signifying a one-year surge of 864,016 cases—a staggering increase of 9,024.6 percent.

In 2022, the incidence of flu cases reached 1,699 per 100,000 people, marking a sharp surge of 8,842.1 percent compared to the 19 cases per 100,000 people reported in 2021.

Nevertheless, the current incidence of flu cases, as observed in 2022, remains lower than the pre-Covid-19 pandemic levels. In 2018, there were 2,723,341 reported flu cases, which decreased to 1,774,635 in 2019—the year preceding the outbreak. The advent of the Covid-19 pandemic led to a significant drop in flu cases, with 2020 recording 783,505 cases, followed by a further decline to 9,574 cases in 2021. As life gradually returned to normal in 2022, there was a notable spike in flu cases to 873,590—approximately half the number reported in 2019. Consequently, over the past four years, there has been a consistent annual decline in flu cases at an average rate of 24.7 percent.

In 2022, adolescents emerged as the predominant age group affected by flu cases, constituting 39.7 percent of the total cases, equivalent to 347,017 individuals. The age group of 9 and under comprised 25.9 percent, accounting for 225,727 cases. Subsequently, those in their 20s represented 13.2 percent with 115,564 cases, individuals in their 30s accounted for 9.3 percent with 81,537 cases, and those in their 40s constituted 7.4 percent with 64,571 cases.

Health insurance medical expenses for flu patients increased by 3,303.8 percent (83.3 billion won) from 2.5 billion won in 2021 to 85.8 billion won in 2022. However, over the past four years, flu medical expenses have decreased by an average of 27.4 percent per year.

The cost per flu patient decreased by 62.7 percent from 263,000 won in 2021 to 98,000 won in 2022. The age group with the highest per capita flu expenses in 2022 was those aged 80 and older, at 598,000 won.

Jung Woo-yong, a professor in the Department of Infectious Diseases at NHIS Ilsan Hospital, commented on the impact of Covid-19 on the incidence of respiratory infectious diseases such as the flu. He noted, "Due to Covid-19, there was a decrease in the occurrence of respiratory infectious diseases as individuals adhered to personal hygiene practices and restricted social movement and contact." He further explained, "With the gradual return to normalcy, the mandatory mask-wearing, except in vulnerable facilities like hospitals, was lifted. This led to an increase in patients due to heightened movement and contact, coupled with increased susceptibility within the population that had regained immunity, resulting in a continuous rise in flu cases."

Regarding the elevated number of flu cases among teenagers, Professor Jung attributed it to the nature of students living in communal settings, primarily in schools and cram schools, making them more susceptible to virus exposure and facilitating the easy spread of respiratory infectious diseases.