On Dec. 12, 2025, the Center for Infectious Disease Research & Policy (CIDRAP) reported COVID-19 rates in the United States and Europe remain low, but influenza and respiratory syncytial virus (RSV) activity is ramping up in both regions, with a surge in flu cases in the United Kingdom in the past week.

In addition, the emergence of the influenza A H3N2 subclade K virus fueled a record number of flu cases in Australia this year and extended the season in both that country and New Zealand—which may portend a longer-than-normal season in the Northern Hemisphere, according to a rapid communication published yesterday in Eurosurveillance.

Flu cases continue to creep upward in most areas of the United States, although care-seeking for acute respiratory disease is low overall, the Centers for Disease Control and Prevention (CDC) said in its weekly respiratory illness update. The CDC reported that wastewater concentrations of COVID-19, flu, and RSV are low, but WastewaterSCAN weekly data show high levels of SARS-CoV-2.

RSV cases are increasing in the Southeast, South, and Mid-Atlantic regions, and emergency department visits and hospitalizations are rising among children aged 0 to 4 years, the CDC noted. 

Cases of “walking pneumonia” caused by Mycoplasma pneumoniae bacteria have been elevated in some parts of the country over the past few weeks, and pertussis (whooping cough) infections are elevated but lower than their November 2024 peak.

In the European Union, flu activity rose three or four weeks earlier than in the previous two seasons, and the number of patients seeking primary care for respiratory disease is elevated in about half of reporting countries, the European Centre for Disease Prevention and Control (ECDC) said in its weekly communicable disease threats report. 

Influenza circulation in Europe continues to pick up, with most countries documenting widespread activity of low to moderate intensity. Cases are highest in the five- to 14-year-old age-group, and increased hospital admissions are being seen in some countries, especially among adults aged 65 years and older.