U.S. flu vaccines are likely to move from quadrivalent to trivalent due to a change in circulating influenza viruses, says a University of Michigan researcher.

Currently, all influenza vaccines in the United States are quadrivalent, meaning that they protect against four different flu viruses.

In a new paper published in the New England Journal of Medicine, researchers detail the spread of influenza B/Yamagata virus, which has not been in circulation since early 2020; the regulatory discussions and recommendations on updating vaccines; and the manufacturing considerations for new vaccine formulations for the U.S. and abroad.

“The removal of B/Yamagata virus is logical as we do not want to include a virus in vaccine formulation that is no longer in circulation,” said Arnold Monto, professor emeritus of epidemiology and global public health at the U-M School of Public Health.

“It also gives us the space to replace B/Yamagata virus with a component that will give improved protection against the circulating influenza viruses. That will take additional studies to accomplish.”

Monto has dedicated his career to researching the occurrence, prevention and control of respiratory infections. He also serves as a member of the U.S. Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee.

Co-authors include Maria Zambon of the U.K. Health Security Agency and Jerry Weir of the Division of Viral Products, Center for Biologics Evaluation and Research at the U.S. Food and Drug Administration.