The national influenza (flu) vaccination for the 2026~2027 season began on the 21st. Since last year, the national immunization vaccine was switched to the trivalent vaccine, but this year, citizens who are not eligible for national immunization can effectively only receive the trivalent vaccine when paid at hospitals and clinics, raising curiosity about whether the quadrivalent vaccine is better. According to the Korea Disease Control and Prevention Agency, all influenza vaccines distributed domestically this year are trivalent vaccines. In the past, even if trivalent vaccines were used in the National Immunization Program (NIP), some medical institutions could pay for quadrivalent vaccines, but this year, manufacturers have not applied for approval for the quadrivalent vaccine, effectively eliminating the option. Because of this, some citizens preparing for vaccination are questioning, "Isn't the quadrivalent vaccine better?" and "Isn't the preventive effect reduced by switching to the trivalent vaccine?" The difference between the trivalent and quadrivalent vaccines This refers to the number of virus types included, where 'price' refers not to the price but to the number of antigens or virus strains included in the vaccine. While the existing quadrivalent vaccine contains antigens from four strains—A H1N1, A H3N2, B type Victoria, and B type Yamagata—the trivalent vaccine contains three antigens: A H1N1, A H3N2, and B type Victoria, excluding the B Yamagata lineage. The Yamagata B strain, which was excluded from the quadrivalent vaccine, has not been detected worldwide for a long time since the COVID-19 pandemic. In response, the World Health Organization (WHO) recommended switching seasonal influenza vaccines to trivalent vaccines starting in 2024, and South Korea has been applying trivalent vaccines for national immunization starting from the 2025~2026 season after review by the Immunization Specialist Committee. Currently, the Yamagata B virus has not been detected for a long time, It is believed that there is no difference in the preventive effectiveness between the trivalent and quadrivalent vaccines, and in fact, the U.S. has switched to trivalent vaccines starting from 2024~2025, and countries like Japan, the U.K., and Taiwan are also successively switching to trivalent vaccines.
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