Is Influenza B/Yamagata extinct?

Influenza A virusses are divided into almost countless subtypes. These subtypes are named after the glycoproteins hemagglutinin (H) and the neuraminidase (N) that are found on the surface of the virus. At the moment there are at least 18 different subtypes of hemagglutinin and 9 different subtypes of neuraminidase. Almost all possible combinations have been found in birds, the remaining in bats.

Influenza B doesn’t have subtypes, but its viruses divide into two 'lineages', B/Victoria and B/Yamagata. Usually, only one of the Influenza B viruses was included in the yearly Influenza vaccines. Which might or might not work against the prevailing virus.

But the measures we have taken to manage the corona pandemic may have solved this problem. Measures like mask wearing, school closures, and travel restrictions were driving influenza transmission rates to historically low levels around the world. It appears that Influenza B/Yamagata might even have gone extinct.

It hasn't been spotted in over a year. In fact, March 2020 was the last time viral sequences from Influenza B/Yamagata were uploaded into the international databases used to monitor flu virus evolution.

It would be time to celebrate if only we knew that humans were the only host of Influenza B. Sadly, that is not the case. While some medical textbooks still maintain that the Influenza B Virus is only infecting humans, current research has indicated that this view is redundant. It is now known to infect seals and horses.

e So, it may hide in other animals, waiting to infect us again and in the mean time, it may mutate.