The Pan American Health Organization (PAHO) has issued an epidemiological alert urging countries in the Region of the Americas to adjust their health service preparation and organization plans in anticipation of the upcoming winter season and the increased circulation of influenza and other respiratory viruses in the Northern Hemisphere.
PAHO emphasized that a combined strategy of vaccination, epidemiological surveillance, hospital preparedness, timely diagnosis and treatment, along with personal preventive measures, will be key to mitigating the disease burden, protecting vulnerable populations, and avoiding the risk of overloading health systems.
Influenza Activity in the Region
According to data reported through the end of November, influenza activity continues to rise globally, driven by a type A virus. While levels are still low in the Americas, a sustained increase is being recorded, especially in North America.
Caribbean and Central America: The circulation of the influenza A(H1N1)pdm09 virus predominates.
Canada and the United States: A greater presence of the A(H3N2) subtype is observed, including the progressive detection of the K sub-lineage, already identified in Europe and Asia.
This includes ensuring the continuous reporting of data and the regular sending of samples for genetic sequencing, which allows for the timely detection of variants that could alter the transmission or severity of the viruses.
Other key recommendations include:
- Updating national clinical management guidelines and ensuring access to early diagnosis and the availability of antivirals for people at high risk of complications.
- Preparing health services for a possible increase in hospitalizations during the Northern Hemisphere's winter months, when the circulation of multiple viruses will coincide.
- Reiterating the importance of influenza, COVID-19, and RSV vaccination, focusing on risk groups such as the elderly, people with chronic diseases, pregnant women, young children, and health workers.
Finally, PAHO reminded of the obligation to investigate and promptly communicate unusual respiratory events, such as severe cases without an identified cause or outbreaks outside the expected circulation period, in accordance with the International Health Regulations.
It is relevant that, until early November, the K sub-lineage had not been detected in South America.
SARS-CoV-2 (COVID-19): Its detection was higher at the beginning of 2025, with a subsequent predominance of the XFG variant, with no signs of greater severity.
PAHO's Strategic Recommendations
PAHO urged countries to strengthen influenza, RSV, and SARS-CoV-2 surveillance.
PAHO warns that seasons dominated by A(H3N2) tend to affect the elderly more severely.
The continental body noted that preliminary evidence suggests that the current vaccine maintains protection levels comparable to previous seasons, particularly for preventing severe cases and hospitalizations.
Balance of the Season in the Southern Hemisphere
The Southern Hemisphere closed its winter season with a 29% increase in reported severe acute respiratory infection cases, compared to 2024.
Respiratory Syncytial Virus (RSV): It notably affected infants under six months of age.
Influenza: It mainly affected the elderly, with circulation initially dominated by A(H1N1)pdm09 and then by A(H3N2), without greater severity being observed.
