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Shot in the arm: Changes to US flu vaccine are planned

Changes in influenza circulation means that the U.S. is likely to see vaccines move from quadrivalent to trivalent models.


Seasonal influenza kills up to 650,000 people every year, according to the World Health Organization. This is why influenza vaccinations are so important, especially to protect young children, older people, pregnant women, or people who have vulnerable immune systems.

However, the vaccine is not static and it needs to be updated each year. There are also decisions taken about how many strains of the virus a given vaccine is designed to be effective against. These decision require epidemiological data and often result in change.

Changes in influenza circulation means that the U.S. is likely to see vaccines move from quadrivalent to trivalent models. This is a necessary change due to a change in circulating influenza viruses, based on University of Michigan research.

Currently, all influenza vaccines in the U.S. are classed as quadrivalent, meaning that they protect against four different flu viruses. Specifically, a quadrivalent influenza (flu) vaccine is designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses.

The reason for introducing this types of vaccines was because: “conventional trivalent influenza vaccines have shown a limited ability to induce effective protection when major or minor mismatches between the influenza B vaccine component and circulating strains occur.”

In a new paper, published in the New England Journal of Medicine, researchers have detailed the spread of influenza B/Yamagata virus, which has not been in circulation since early 2020. The paper also discusses the regulatory resultant discussions and recommendations on updating vaccines, together with 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,” Arnold Monto, professor emeritus of epidemiology and global public health at the U-M School of Public Health outlines in a statement.

Monto adds: “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.

The research paper is titled “The End of B/Yamagata Influenza Transmission—Transitioning from Quadrivalent Vaccines.”

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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