Mexico Urges Mask Use, Vaccination After H3N2 Subclade K Case

Mexico’s Ministry of Health recommends targeted mask use and renewed influenza vaccination after confirming the country’s first case of influenza A(H3N2) subclade K, a variant that has expanded across parts of the European Union, North America, and East Asia but has not shown increased severity.

The guidance was announced as global health agencies, including the Pan American Health Organization (PAHO) and the World Health Organization (WHO), report a rapid rise in detections of the H3N2 subclade K in multiple regions, prompting governments to reinforce seasonal influenza prevention measures ahead of winter peaks.

David Kershenobich, Minister of Health, says the recommendation to wear face masks applies to people experiencing flu symptoms, with the aim of limiting transmission rather than signaling a broader public health emergency. Speaking during the presidential morning briefing, Kershenobich said the confirmed case in Mexico was identified about a month ago through routine epidemiological surveillance, and resolved without complications. “The patient was treated on an outpatient basis with oseltamivir and responded well,” he said, adding that the individual did not require hospitalization and has fully recovered.

Kershenobich says the clinical behavior of the case was consistent with seasonal influenza and that no additional infections linked to the subclade have been detected in the country. He adds that people who test positive for influenza should follow standard isolation guidance and receive timely treatment, while managing symptoms with commonly used medications such as paracetamol.

The Ministry of Health’s recommendations come amid heightened attention to influenza A(H3N2) subclade K, which international health authorities describe as more transmissible than some previous strains but not more severe. PAHO and WHO have reported that the variant has accumulated genetic changes, including amino acid substitutions in the hemagglutinin protein, and has evolved from related J.2.4 strains. Despite these changes, available data show no significant increases in hospitalizations, intensive care admissions, or deaths.

According to WHO, subclade K became more prominent in Australia and New Zealand beginning in August and has since been identified in more than 34 countries over the past six months. In the European Union, it accounted for nearly half of reported influenza sequences during an early start to the season, while the United States and Canada have reported a steady rise in detections. South America has remained largely unaffected so far, although health authorities continue to monitor trends closely.

In Mexico, officials say surveillance data do not indicate widespread circulation of the variant. The National Epidemiological Surveillance System continues routine monitoring, including genomic sequencing, as part of preparations for the winter respiratory virus season. Health authorities emphasize that H3N2 strains circulate globally each year and that ongoing surveillance is designed to detect changes in transmission patterns or clinical impact.

Vaccination remains a central element of Mexico’s response. Kershenobich says there is sufficient supply of influenza vaccines and antiviral treatments nationwide, and that the vaccine available in the country, Mexinvac, has been in use since 2024. He says the influenza vaccine provides protection against the circulating H3N2 variant, including subclade K.

As of mid-December, vaccination coverage stood at about 50% of the target population, according to the Ministry of Health. Officials urge eligible groups to seek immunization at health centers and authorized medical units to reduce the risk of infection and complications. Priority groups include children aged six months to five years, adults 60 and older, and people with underlying conditions such as diabetes, hypertension, chronic kidney disease, obesity, asthma, or compromised immune systems.

International data cited by PAHO and WHO suggests that, despite antigenic differences in subclade K, vaccine effectiveness against hospitalization remains comparable to previous seasons. Preliminary estimates indicate effectiveness of roughly 70% to 75% in children and 30% to 40% in adults. Health authorities say maintaining high vaccination coverage is critical to limiting the impact of influenza during periods of increased transmission.

PAHO and WHO urge the Americas to strengthen genomic surveillance, ensure timely access to antiviral treatment, and prepare health systems for the possibility of earlier or more intense influenza activity during the 2025–2026 season. The agencies have stressed that vaccination is especially important for older adults and people with risk factors, both to protect individuals and to reduce pressure on hospital services.

Mexico’s winter vaccination campaign also includes COVID-19 and pneumococcal vaccines, administered according to eligibility criteria. Health officials say the combined approach is intended to reduce the overall burden of respiratory illness and prevent complications, particularly among children, older adults, pregnant women, healthcare workers, and people with chronic conditions.

Authorities underscore that the current recommendations, including mask use for symptomatic individuals, are precautionary and aligned with standard public health practice during influenza season. The Ministry of Health says it will continue to provide updates as new information becomes available and has reiterated that, at present, the situation does not represent a broader public health risk for the country.