A nationwide flu epidemic has been declared in Japan after cases topped 6,000, with more than a hundred schools forced to temporarily close. A level of diffusion considered out of scale for the period: the flu season in the country usually only begins between the end of November and the beginning of December.
This year, however, infections increased already in September, approximately five weeks earlier. The surveillance laboratories speak of an unusual dynamic, probably linked to a combination of environmental and social factors.
An advance that surprises the experts
Virologist Vinod Balasubramaniam, from Monash University Malaysia, explained to Nature that early growth “has never been observed at these levels” and could be influenced by greater international mobility after the end of Covid-related restrictions, by climate variations that alter respiratory seasons and by lower natural immunity in children and the elderly, less exposed to the virus in recent years.
According to epidemiologists, the increase in contacts between regions and countries is shortening the distances between the flu seasons of the two hemispheres, changing the traditional balance between the North and South of the world.
The role of the H3N2 strain
The virus most under observation is the influenza A (H3N2) strain, already responsible for a sharp increase in cases in Australia and New Zealand during the southern winter.
As Ian Barr, deputy director of the WHO Collaborating Center for Influenza Research in Melbourne, pointed out, “it is likely that the circulation of the H3N2 strain was accelerated by travel between hemispheres, particularly to Japan, where tourism has returned to pre-pandemic levels.”
Genetic analyzes on the Japanese samples are underway, but the first data seem to confirm the presence of this same strain, already known for its ability to mutate rapidly and spread easily.
The most vulnerable groups and school closures
Of those hospitalized in September, nearly half were under 14, pointing to schools as a major hotbed. Several prefectures have opted for the temporary suspension of lessons and the return to precautionary measures, such as the use of masks and the limitation of group activities.
Even in Malaysia the infection curve follows a similar trend: almost 6,000 students affected and 97 school outbreaks recorded in just one week, a sign that the Asian region is facing an early and intense flu season.
The risks for Europe
For now, the situation remains confined to Asia, but the phenomenon is also being carefully observed by European health authorities.
Infectious disease specialist Matteo Bassetti highlighted that “the H3N2 and H1N1 strains currently circulating in Japan will be the same ones that will probably reach Italy and Europe in the coming weeks”.
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The fear is not so much that of a new global emergency, but of an earlier and larger flu season than historical averages. If confirmed, the Japanese advance could in fact change vaccination and surveillance strategies in the Old Continent.
