The Pan American Health Organization (PAHO/WHO) has warned of rising influenza activity in several countries across the Southern Hemisphere as the region enters the respiratory virus season, urging countries to strengthen disease surveillance, expand vaccination efforts, and bolster health system preparedness. 

Seasonal influenza remains a major cause of illness and death worldwide. According to World Health Organization (WHO) estimates, influenza causes between 3 million and 5 million severe cases and up to 650,000 respiratory-related deaths each year. In the Americas, it is responsible for an estimated 772,000 hospitalizations and between 41,000 and 72,000 deaths annually.

Although influenza A remains the dominant virus across the region, health authorities have observed a recent increase in the circulation of influenza B in several Southern Cone countries. The trend coincides with the circulation of other respiratory viruses, including respiratory syncytial virus (RSV), whose activity has also increased in recent weeks. This situation could place additional pressure on health systems, particularly affecting children under five years of age and older adults. 

“The co-circulation of influenza and other respiratory viruses could lead to a significant increase in outpatient visits, hospitalizations, and demand for pediatric and intensive care beds, placing additional strain on health services, particularly during periods of peak viral circulation,” PAHO said in a new epidemiological alert. 

Influenza B rising during a season still dominated by influenza A

Globally, influenza activity is following expected seasonal patterns. While the Northern Hemisphere is currently experiencing an inter-seasonal period marked by low viral circulation, influenza activity is increasing across the Southern Hemisphere. Although influenza A—particularly the A(H3N2) subtype—remains predominant, influenza B circulation has been rising steadily in recent weeks. 

In the Americas, the trend has been especially evident in Southern Cone countries, notably Brazil and Chile, where the proportion of influenza B cases has increased alongside a broader rise in other respiratory infections. While there is no evidence so far that disease severity has exceeded expected seasonal levels, increased circulation of respiratory viruses could result in higher numbers of outpatient visits and hospital admissions in the coming weeks.