Avian Influenza Spreading Rapidly: "Stronger Virus, Yet Quarantine Violations Persist" [Why&Next]

32 Cases Reported This Winter, Far Exceeding Last Winter's 25
Infectiousness Ten Times Higher, Shorter Time to Death
Most Confirmed Farms Violated Quarantine Protocols

Recently, highly pathogenic avian influenza (AI) has been spreading rapidly during the winter season. In this winter season alone (2025-2026), there have already been 32 cases of AI outbreaks at poultry farms, surpassing the 25 cases recorded during the same period of the previous winter season (as of January 5, 2025). The government analyzes that the continued occurrence of AI is due to the detection of a greater variety of viruses than usual, the strong infectiousness of the current strains, and the ongoing failure of some farms to comply with basic quarantine protocols.

According to the Central Accident Management Headquarters for Highly Pathogenic AI on January 6, H5N1-type highly pathogenic AI was confirmed the previous day at a layer breeder farm in Chungju (with 40,000 birds) and a broiler breeder farm in Iksan, North Jeolla Province (with 63,000 birds). As a result, since the first case at a native chicken farm in Paju on September 12, 2025, there have been a total of 32 AI outbreaks during the 2025-2026 winter season.

This winter season marks the first time in Korea that three types of viruses-H5N1, H5N6, and H5N9-have been detected in both wild birds and poultry farms. An official from the Ministry of Agriculture, Food and Rural Affairs explained, "Of the total 32 cases, 31 were H5N1 and one was H5N9. In the case of H5N6, it was detected only at farms where preemptive culling took place, so it was not included in the total outbreak count."

In particular, the H5N1 virus detected in Korea this winter season has proven to be more potent than in previous years. According to an analysis by the Animal and Plant Quarantine Agency, the viral concentration required to kill half the chickens (the median lethal dose) was 10 to the power of 3.3, which is about one-tenth of the levels seen in 2023-2024 (10 to the power of 4.4) and 2024-2025 (10 to the power of 4.6). A representative from the Quarantine Agency explained, "This means that the disease can now spread much more easily in poultry farms, even with just one-tenth the amount of virus compared to previous years."

The time it takes for chickens infected with AI to die has also shortened. All naturally infected chickens died, and the average time from infection to death during this winter season was 2.4 days-the shortest since the 2020-2021 winter season, when the range was 2.6 to 4.3 days.

Most farms where AI outbreaks occurred were found to have violated quarantine protocols. According to the Quarantine Agency, a mid-term epidemiological investigation of 30 farms where AI occurred between September 12 and January 3 found that none of the farms complied with basic quarantine rules. For example, some farms failed to insulate disinfection equipment during the winter, causing it to freeze; as a result, people and vehicles entered the farms without undergoing disinfection. In addition, vehicles transporting eggs and other products are required to use transfer stations outside the farm to prevent virus introduction, but some violated this rule and entered directly into the farm premises.

On the 5th, Song Miryung, Minister of Agriculture, Food and Rural Affairs, chaired a quarantine measures meeting to review the situation of highly pathogenic avian influenza outbreaks and quarantine measures. Ministry of Agriculture, Food and Rural Affairs

With the risk of further AI outbreaks increasing, the government held a quarantine measures meeting on the previous day, presided over by Song Miryung, Minister of Agriculture, Food and Rural Affairs, and is now implementing even stricter quarantine management. To prevent additional outbreaks at layer farms, the government will assign dedicated supervisors to each of the 539 layer farms nationwide (with more than 50,000 birds) for two weeks until January 16, to control the entry of livestock vehicles and intensively monitor for any violations of quarantine regulations. In addition, to eliminate sources of contamination inside and outside poultry farms, livestock facilities, and vehicles, the government is conducting intensive disinfection at least twice daily until January 14 on roads near migratory bird habitats and nearby poultry farms.

An official from the Central Accident Management Headquarters stated, "With the AI virus now being more infectious, it is even more critical to strictly follow quarantine protocols, yet many farms are failing to do so. If these protocols are not observed, the risk of AI spreading increases significantly, so it is essential for farms to rigorously enforce basic measures such as restricting entry of external vehicles and changing boots at the farm level."