Foreign residents in Tokyo should be on alert as influenza cases have nearly doubled in the capital, with a concerning shift toward Influenza B type infections that can be harder to detect than the more common A strain. According to NHK, Tokyo's influenza patient numbers have surged to nearly twice the previous week's levels as of early February 2026. Medical facilities across the city are reporting a notable increase in Influenza B diagnoses, a development that health experts say requires heightened awareness among residents. Unlike the more familiar Influenza A strain, Influenza B presents unique challenges for detection and prevention. As reported by Livedoor News, this strain is characterized by its tendency to spread unnoticed because infected individuals may not develop the high fever typically associated with influenza. This "silent spread" makes it particularly dangerous in workplaces, schools, and other communal settings where people might continue their daily activities while unknowingly transmitting the virus. The milder initial symptoms of Influenza B can be deceptive. While Influenza A often announces itself with sudden high fever, body aches, and severe fatigue, Influenza B may begin with more subtle signs that could be mistaken for a common cold. Patients might experience mild respiratory symptoms, slight body discomfort, or general malaise without the dramatic fever spike that would normally prompt them to stay home or seek medical attention. For expats living in Japan, this situation requires particular vigilance. The Japanese healthcare system operates differently from many Western countries, and understanding when and how to seek treatment is crucial. If you experience any respiratory symptoms, even mild ones, during this surge period, consider visiting a clinic for testing. Most Japanese clinics can perform rapid influenza tests that provide results within 15-20 minutes. The timing of this surge is significant. February typically marks peak influenza season in Japan, and the shift toward B type infections adds complexity to an already challenging period. The strain's ability to spread without obvious symptoms means that workplace attendance policies and personal health monitoring become even more important. Expats should be aware that Japanese workplace culture often emphasizes attendance, but during this outbreak, staying home when feeling unwell is both socially responsible and increasingly accepted. Many companies have adapted their policies in recent years to discourage presenteeism during infectious disease outbreaks. Prevention remains the most effective strategy. Health authorities recommend standard infection control measures: frequent handwashing with soap and water, using alcohol-based hand sanitizers, avoiding touching your face, and maintaining distance from people showing respiratory symptoms. In crowded public spaces like trains and shopping centers, wearing a mask provides an additional layer of protection and is widely practiced in Japan. For those who haven't received this season's influenza vaccination, it's worth consulting with a healthcare provider about whether vaccination is still advisable. While the vaccine's effectiveness may be reduced later in the season, it can still provide some protection and reduce symptom severity if infection occurs. Expats with children should be especially attentive, as schools and daycare facilities can become transmission hotspots. Monitor children for any symptoms, even mild ones, and keep them home if they show signs of illness. Japanese schools typically require a doctor's clearance before students can return after influenza diagnosis. The current situation underscores the importance of understanding Influenza B's unique characteristics. Its subtle presentation means that the usual "wait and see" approach to mild symptoms may not be appropriate during this surge. Early detection through testing allows for appropriate treatment with antiviral medications, which are most effective when started within 48 hours of symptom onset. As Tokyo navigates this influenza surge, foreign residents should remain informed, practice diligent hygiene, and seek medical attention promptly when symptoms appear, regardless of their severity.