Historical annual reformulations of the influenza vaccine

Since 1999, the World Health Organization has issued annual recommendations for influenza vaccine formulations. One reformulation of the influenza vaccine is for the Northern Hemisphere, and the other is for the Southern Hemisphere. Both recommendations are trivalent, i.e. featuring three strains.

Contents

• Northern Hemisphere recommended strains
• Southern hemisphere recommended strains
• References

Since the 2012–13 season, the WHO recommendations have also included the formulation of an annual quadrivalent vaccine, featuring an additional B-strain.