Sanofi Pasteur seeks to expand seasonal flu protection from three influenza strains to four

 SWIFTWATER, Pa. — Sanofi Pasteur on Thursday announced it has filed for approval of a four-strain flu shot to the Food and Drug Administration. An action date is anticipated in the second quarter of 2013. 

"The addition of a fourth influenza virus strain to the seasonal influenza vaccine formulation has the potential to make a substantial impact in reducing influenza disease and influenza-related complications, hospitalizations and deaths among those who contract the disease," stated David Greenberg, senior director, U.S. scientific and medical affairs, Sanofi Pasteur. "Two influenza B-lineage strains typically co-circulate in the U.S each year, so it makes sense to include both in the vaccine rather than attempting to predict which of the two will be the dominant strain. In fact, in six of the past 12 influenza seasons, the B strain selected by health authorities for inclusion in the vaccine was not the predominant B-lineage strain that circulated during the next influenza season."

The strains for each season's influenza vaccine are selected by the FDA, in consultation with global health authorities, from the strains anticipated to circulate in the approaching influenza season. Seasonal influenza vaccines contained only two strains (one strain of type A influenza and one strain of type B influenza) until 1978, when the decision was made to incorporate a second type A influenza strain in order to provide protection against the two different A strains that were co-circulating. From then until now, influenza vaccines have been trivalent to help protect against three strains of influenza virus (two of type A and one of type B). 

However, since the influenza B Victoria lineage re-emerged worldwide in 2001-2002, two influenza B strains (one each from the Victoria and Yamagata lineages) have co-circulated with varying prevalence, making it difficult to predict the next season's dominant B strain. Even in years when the correct B virus strain was selected for the vaccine, some influenza disease was caused by the B strain omitted from the vaccine. These factors raised the hypothesis that the addition of a second B-lineage strain to expand the licensed trivalent influenza vaccine to a quadrivalent vaccine could help reduce flu incidence.