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Data InsightsA flu strain has likely gone extinct since 2020

A flu strain has likely gone extinct since 2020

A line graph titled "Confirmed cases of influenza B Yamagata" shows weekly confirmed cases of B Yamagata influenza worldwide from various types of influenza surveillance. The vertical axis represents the number of cases, ranging from zero to 5,000, while the horizontal axis covers the years from 2013 to 2025. The graph indicates significant fluctuations in case numbers over the years, with a noticeable peak just below 5,000 cases around 2019, followed by a steep decline. A data source note mentions that only a fraction of potential influenza cases is tested by labs for confirmation and strain identification. The data comes from FluNet, World Health Organization, and is dated 2023. The graph is licensed under CC BY.

Flu viruses spread every year and cause seasonal outbreaks. But one type, called influenza B Yamagata, .

The chart shows global confirmed cases of B Yamagata flu over time. Before 2020, it peaked each flu season. However, no confirmed cases have been reported worldwide in the last five years.

This because COVID-19 precautions — such as social distancing, masks, and travel restrictions — sharply reduced social contact. With fewer opportunities to spread from person to person, B Yamagata couldn’t sustain transmission and eventually died out.

Regulatory health agencies like the WHO, European Medicines Agency, and US CDC have removing it from flu vaccines. This could allow room for other strains to be included in seasonal flu vaccines, .

Explore the data on influenza in our data explorer →

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