The full effect of the introduction of quadrivalent flu vaccines is unlikely to become clear for several years, but this week saw the release of data that convinced the FDA to approve GlaxoSmithKline's ($GSK) vaccine. And while the benefit of the extra strain is unclear, the data makes a case for immunizing with any flu vaccine.
GSK published data from one of the pivotal studies that led to FDA approval in The New England Journal of Medicine. The trial administered either the quadrivalent flu vaccine or a control--GSK's hepatitis A shot, Havrix--to more than 5,000 kids in Bangladesh, Honduras, Lebanon, Turkey and several other countries. After monitoring the kids for 6 months, GSK estimated the quadrivalent vaccine efficacy was 59%. Lab-confirmed influenza was seen in 5.7% of the control group, compared to 2.4% of kids in the vaccine arm.
The data were strong enough for GSK to meet its primary endpoint but do little to show the benefit of quadrivalent vaccines over trivalent vaccines. In the whole study, only two cases of influenza were caused by the extra B strain the quadrivalent vaccine protects against. Both of these were in the control group in the Philippines. Prolonged, real-world use could generate more compelling data. "The true value of the [quadrivalent vaccine] will be seen in years when the two B lineages are cocirculating," GSK wrote.
Cocirculation of the two B strains has happened over the past 12 years, as have shifts in the dominant lineage from season to season. This makes it difficult to predict which strain to use in a trivalent vaccine. In 2007, health officials made the wrong choice. B/Yamagata was dominant, accounting for 98% of B strains, but the trivalent vaccine only protected against the two A lineages and B/Victoria. It is estimated that a quadrivalent vaccine would have prevented 440 influenza-associated illnesses.