One strain of the influenza virus that infected millions and targeted children has disappeared from the earth, and experts are completely certain about its extinction. They believe it should be removed from vaccines. This "extinct" virus belongs to the influenza B family, known as the Yamagata strain (one of the two influenza B strains that cause seasonal flu).
At the start of the influenza season, vaccines typically protect against four strains of the virus: two type A strains and two type B strains. Last week, a committee of experts advising the U.S. Food and Drug Administration (FDA) on vaccines unanimously voted to eliminate one of the four annual vaccines, excluding the influenza B branch known as Yamagata.
With the spread of the coronavirus, precautions taken to stop the spread of COVID-19, such as masks and social distancing, have led to a historic low in influenza cases, to the point that the Yamagata strain, one of two influenza B viruses alongside the Victoria virus, has been eradicated. The two strains separated in the 1980s but remained closely linked.
However, they are not the deadliest or fastest-evolving viruses. Because they evolve slowly, immunity typically lasts longer, meaning that adults are less likely to become infected. Influenza B viruses tend to cause more illness in children, who have not been exposed to them as much. Meanwhile, influenza A viruses, such as the familiar H1N1 strain, are generally more concerning, being the types that cause pandemics, like the Great Influenza of 1918 that killed an estimated 50 million people.
Influenza B viruses are known not to have caused a global pandemic, and with the apparent absence of Yamagata from the scene, the FDA and the World Health Organization (WHO) agreed that there is no longer a need to include it in the seasonal influenza vaccine list. The FDA stated, "In the interest of public health, the FDA strongly advised influenza vaccine manufacturers to remove the Yamagata/B (B/Yamagata) strain from the seasonal influenza vaccines in the United States for the 2024-2025 flu season. The FDA is working with manufacturers to transition from quadrivalent seasonal influenza vaccines to trivalent seasonal influenza vaccines in the upcoming flu season."
Although health experts have agreed to remove this strain from upcoming flu vaccines, industry workers argued that manufacturers will need time to shift to the new formulation.
