FDA panel debates adding a fourth strain to influenza vaccine

Predicting which influenza strains will be infecting people across North America can be a rather unscientific endeavor at times. For years, U.S. pharmaceutical manufacturers have produced influenza vaccines that are a combination of three strains—two A strains and a B strain. While this current season’s A strains match what is circulating fairly well, there have been mismatches in recent years. Guessing the dominant B strain from year to year has been even more challenging, said Rakesh Pandey, who is a researcher with FDA’s Division of Vaccines and Related Products Applications. FDA advisers are intensifying discussion about whether to add a second B strain for future flu seasons. The possibility of a four-strain, or quadrivalent, vaccine was discussed February 18 during FDA’s Vaccines and Related Biological Products Advisory Committee meeting in Silver Spring, Maryland. Each influenza season since 2000 has been characterized by two different B strains circulating at the same time. It is almost impossible to predict which strain will be the dominant one in any given influenza season, Pandey explained.