COVID may have pushed a leading seasonal flu strain to extinction

Not even seasonal fluviruses were spared by the debut of the coronaviruses. The 2020-2021 flu season was all but canceled due to travel restrictions and other precautions. That meant a dramatic collapse in the genetic diversity of circulating flu strains, as well as a decrease in the number of people sick with the flu. The viruses were all but gone. One of the four flu groups that were targeted by the seasonal vaccine went completely dark.

The flu was still struggling to recover from its Pandemic knockout when researchers noticed the absence last year. The flu could cause a nasty season in the Northern Hemisphere. According to a study published this week in the journal Eurosurveillance, theInfluenza B/Yamagata lineage is still missing. Since April 2020, it hasn't been found. Is it really gone extinct?

Future flu seasons and flu shots could be affected by B/Yamagata's absence. Seasonal flu has been circulating among humans in recent years. There are two types of flu: H1N1 and H3N2. The other two are related to the Victoria and Yamagata families. Check out our explainer for more information. Each of the four types of flu viruses have their own vaccine versions.

Seasonal shots are more effective when there are fewer flu viruses around. As time passes and people lose immunity, B/Yamagata could become more dangerous. Health experts want to know if B/Yamagata is still around.

Vanished virus

In an article published this week in the journal Eurosurveillance, researchers in the Netherlands looked for the missing strain of flu. After March 2020, there will be no B/Yamagata sequence with specimen collection data in the database.

There have been 43 reports of the missing lineage, mostly from China, in the World Health Organization's FluNet data over the course of the next two years. There were more than 50,000 detections of B/Yamagata in the year.

There have been a small number of cases in the last couple of years. They may be detecting signatures of B/Yamagata from vaccines that carry live-attenuated Influenza Viruses. They could be the result of a vaccine mistake. This is much more than a hypothetical. A number of B/Yamagata detections in the US and Scotland were found to be from live-attenuated flu vaccines.

The researchers would like to see laboratories increase their efforts to detect Yamagata cases to see if they are still alive. "From a laboratory perspective, we think it would be advisable to increase the ability and capacity to determine the lineage of all detected influenza B viruses around the world as this is critical to determine the absence of B/Yamagata lineage viruses," they conclude. They propose that the World Health Organization set up criteria to determine when a lineage could be declared "extremittent" and what the consequences would be.