A flu strain has likely gone extinct since 2020
Flu viruses spread every year and cause seasonal outbreaks. But one type, called influenza B Yamagata, may have completely disappeared.
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 likely happened 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 recommended removing it from flu vaccines. This could allow room for other strains to be included in seasonal flu vaccines, improving overall vaccine effectiveness.