The Department of Health (DOH) has confirmed that the Philippines has recorded influenza A(H3N2) subclade K infections nationwide, commonly referred to in media as “super flu”, but officials stress the situation is not cause for alarm based on current surveillance data.
According to the DOH, 77 cases of this variant were detected nationwide as of December 2025, identified from 326 influenza A samples that were successfully genetically sequenced between January and November 2025.
Most patients with the subclade K variant recovered, and no deaths linked specifically to it have been reported, the DOH said, emphasizing that the strain is a variation of seasonal influenza and not a new disease.
Meanwhile, the World Health Organization (WHO) reported that influenza activity has increased globally in recent months and that a particular subclade of influenza A(H3N2), known as J.2.4.1 or subclade K, has risen rapidly in detection across multiple countries since August 2025.
WHO also stated that current epidemiological data do not indicate increased disease severity associated with this variant, but that vaccination remains important to protect against severe illness.
What “Super Flu” actually is and isn’t
“Super flu” is not an official medical classification; rather, it is a media shorthand for a variant of influenza A(H3N2) that has shown increased circulation in late 2025 and early 2026.
The DOH clarified that subclade K symptoms, such as fever, cough, colds, and body aches, are similar to those of typical seasonal influenza and that “the difference is that it spreads more easily.”
According to WHO’s global update, influenza viruses, including A(H3N2), continually evolve through small genetic changes that can affect transmissibility and immune recognition, which is why influenza vaccines are updated each season.
On the other hand, neither the DOH nor WHO has declared subclade K inherently more virulent than earlier seasonal influenza strains, and WHO’s risk assessment specifically states that available data have not shown increased severity for this subclade.
Nevertheless, public health experts caution that increased transmissibility can still lead to substantial impact because a higher number of cases can translate into more hospital visits and potential complications among high-risk groups even if the virus itself is not more severe.
As the U.S. Centers for Disease Control and Prevention noted in its Dec. 19, 2025 respiratory disease season outlook, influenza seasons dominated by H3N2 strains, such as subclade K, have been associated with more hospitalizations and deaths among older people and young children compared with other strains, even though the precise impact of subclade K is unclear and vaccine effectiveness may vary.
READ: WHO Respiratory Virus Updates
Global Influenza trends and Subclade K spread
Globally, WHO’s Dec. 10, 2025 Disease Outbreak News reported that influenza activity has increased since October 2025, with influenza A viruses predominant among detected viruses.
Specifically, the report stated that detections of A(H3N2) subclade K have risen rapidly in many parts of the world, including more than 34 countries, although overall influenza activity remains within expected seasonal ranges. WHO noted that subclade K viruses show genetic drift from related A(H3N2) viruses, but that epidemiological data do not indicate increased disease severity to date.
This global pattern of influenza circulation, especially the predominance of A(H3N2) viruses in many northern hemisphere countries and in tropical areas since late 2025, is consistent with the typical seasonal evolution of respiratory infections, albeit with early or high activity in some regions.
In the United States, the 2025–2026 flu season has been characterized by increasing outpatient visits for influenza-like illness (ILI), and the CDC reported that subclade K comprised approximately 90% of genetically characterized influenza A(H3N2) viruses among U.S. samples collected since late September 2025.
The CDC also noted that this subclade shows differences from the influenza A(H3N2) strain included in the 2025–2026 vaccine, which could influence vaccine effectiveness.
Philippine surveillance
In the Philippines, the DOH’s surveillance data reported in January 2026 confirmed the detection of subclade K cases.
The Philippine Star reported that subclade K accounted for 77 of 92 A(H3N2) cases among sequenced samples, representing 83.7% of those influenza A(H3N2) detections.
The regions with the highest number of cases were the National Capital Region, Calabarzon, and the Cordillera Administrative Region. According to the DOH, most infected patients recovered and there were no fatalities directly linked to subclade K as of December 2025.
Furthermore, the DOH’s public statements around this topic have been consistent: Health Secretary Teodoro Herbosa described the presence of subclade K in the Philippines as “not alarming” during a press briefing, while still urging routine flu precautions such as vaccination and basic health practices.
The DOH also explained that the subclade K variant is part of the broader influenza A category and not a separate new disease, noting that despite increased transmission, most cases have not progressed to severe illness or required hospitalization.
Vaccine efficacy and public health recommendations
In addition to DOH guidance, global and regional health authorities emphasize the continued importance of vaccination. WHO’s influenza risk assessment explains that seasonal vaccines may still provide protection against severe illness and hospitalization, even when circulating viruses have drifted genetically from vaccine strains.
Similarly, the U.S. CDC noted in its Dec. 19, 2025 report that observational studies, such as research conducted in England during significant subclade K activity, suggest vaccines can reduce emergency department visits and hospital admissions by substantial percentages among children and adults, even in the presence of emerging variants.
In the Philippines, health specialists have called on high-risk groups, particularly older adults and individuals with underlying conditions, to seek updated seasonal influenza vaccination once available, and have encouraged practices such as wearing face masks in high-risk settings to reduce transmission.
Seasonality, transmission dynamics, and public health impact
While subclade K is drawing attention because of its spread, it is important to contextualize its emergence within broader influenza patterns. Influenza A(H3N2) has historically been associated with more severe seasonal influenza activity compared with other subtypes, particularly in older populations and young children, due to differences in immunity and virus behavior.
Globally, seasonal influenza causes an estimated 3 to 5 million severe cases and 290,000 to 650,000 respiratory deaths annually, illustrating the persistent threat of flu even in non-pandemic years.
In many countries, increases in acute respiratory infections during typical flu seasons reflect the combined effects of environmental conditions, human behavior, and virus evolution.
Although the Philippines lies in a tropical zone where influenza seasonality can be less pronounced than in temperate regions, sustained influenza activity was observed in tropical areas from mid-2025, with A(H3N2) becoming predominant among influenza detections by the end of the year.
Some public discourse has conflated “super flu” with other respiratory threats such as COVID-19, but the scientific fact is that influenza viruses and SARS-CoV-2 are distinct pathogens with different genetic structures.
However, both can spread through respiratory droplets and aerosols, and both can place pressure on health care systems during peak seasons. This overlap means public health measures like staying home when sick, good hygiene, and protecting vulnerable individuals are relevant for multiple respiratory diseases.
Public health lesson
The verified data from the DOH and WHO paint a clear picture: the so-called “super flu” in the Philippines is a naturally evolved influenza A(H3N2) subclade K variant that has become more detectable in 2025, but it has not demonstrated a significant increase in severity compared with typical seasonal influenza.
Nevertheless, its increased transmission underscores an enduring public health reality, seasonal influenza remains a serious threat that can cause substantial illness and strain health systems, particularly among older adults, children, and people with chronic health conditions.
Concurrently, vaccination and basic preventive measures continue to offer meaningful protection, and their sustained use is essential.
With this, preparedness, grounded in routine surveillance, vaccination uptake, and public health awareness, remains the strongest defense against influenza and similar respiratory viruses.
In a world where respiratory illnesses circulate year-round and evolve continually, vigilance and collective action save lives.
Photo by Maria Kovalets on Unsplash
