Flu activity remains low in Spain, with a small rise among younger people. Data from the southern hemisphere can show which variants are circulating, but it cannot predict Spain's season with certainty.
In week 38, Spain recorded a flu proxy of 22 cases per 100,000 inhabitants. The figure was 18 in the same week of the previous season. Positivity stayed close to 10%.
Data from 7 to 13 September showed an earlier, smaller rise. Influenza positivity in primary care stood at 8.2%, still below the epidemic threshold. The signal is small.
For now, the figures point to limited activity rather than a major wave. The virus is circulating in several regions, and its variants can move between them before their effect becomes visible in Spain. Other respiratory infections also complicate the picture. COVID-19 was rising in Spanish primary care during the same period.
According to the CDC’s September 2026 assessment, influenza activity in the Southern Hemisphere was generally moderate, had peaked and was declining. The agency noted that activity was falling in South America and southern Africa, while it was increasing in Australia but remained low.
The southern hemisphere offers clues, not answers. In the WHO update of 23 September 2026, flu positivity was around 10% in temperate and subtropical areas of the south. It was slightly higher in tropical regions. Activity was uneven, with elevated levels in some countries in South America and in eastern and southern Africa.
Those differences matter. One southern hemisphere figure cannot provide a direct forecast for Spain.
Álvaro Torres Lana is an expert in Public Health and heads the Epidemiological Surveillance and Prevention Unit at the Directorate-General of Public Health of the Servicio Canario de Salud. He says international monitoring is needed to spot changes in viral circulation and variants. His point is practical: southern data can guide preparation, but it does not show how Spain's season will develop.
The two hemispheres do not always follow the same transmission pattern. Tropical regions make the picture harder to read. Influenza can circulate there throughout the year, and those areas can be both sources and recipients of new viral activity.
The ECDC’s weekly European Respiratory Virus Surveillance Summary provides a regional comparison for the EU and European region of the WHO. Alongside southern-hemisphere observations, this European monitoring helps assess whether signals seen in Spain are isolated or part of a broader regional pattern.
Variants are among the most useful early signals. A strain may be identified in one region before it appears elsewhere. Torres Lana says that tracking variants in the south may be one of the best early indicators available. It still cannot provide a complete forecast.
The WHO's vaccine work follows the same logic. On 25 September 2026, the agency updated its recommended composition for the 2027 Southern Hemisphere influenza season after reviewing circulating viruses.
Spain's current figures also show an age-related change. Most detected viruses are influenza A. Hospitalised patients are concentrated mainly among people aged 65 and over. Detections among younger people are starting to rise slightly. That shift needs watching while total activity remains low.
Flu surveillance covers more than infections. Hospital admissions, bed occupancy, intensive-care use and deaths associated with influenza show the pressure on people and the health system. Pharmacy demand for flu medicines and school absences can provide additional clues. These signals may appear before the full burden is visible.
Early monitoring also guides vaccine planning. Laboratories in different countries provide data used to select vaccine strains well before the season starts. It is too early to know how closely this season's vaccine will match the viruses that eventually circulate in Spain.
A poor match can reduce effectiveness. Variant surveillance therefore affects public health directly.
Spain's monitoring of other seasonal risks follows the same need for early warning. An earlier report on weather alerts shows the comparison. It does not change the influenza data. It shows why health decisions depend on tracking conditions before their effects peak.
Vaccination remains focused on reducing severe illness, hospitalisation and deaths. The practical problem is coverage. Prevention must reach vulnerable people who are not vaccinated, and authorities need to identify the health and social barriers that block access.
Spain's surveillance system brings together the autonomous communities. This allows officials to assess respiratory viruses jointly. They can adjust preventive measures and check whether interventions worked.
The evidence supports preparation, not prediction. Flu activity is low but not absent. Variants in the southern hemisphere offer useful signals, but they do not determine Spain's season. Treating them as an exact forecast would be a mistake. Using them to strengthen surveillance and reach vulnerable groups is the responsible response.
