It’s never an easy business to predict which flu viruses will make people sick the following winter. And there’s reason to believe two of the four choices made last winter for this upcoming season’s vaccine could be off the mark.

Twice a year influenza experts meet at the World Health Organization to pore over surveillance data provided by countries around the world to try to predict which strains are becoming the most dominant. The Northern Hemisphere strain selection meeting is held in late February; the Southern Hemisphere meeting occurs in late September.

The selections that officials made last week for the next Southern Hemisphere vaccine suggest that two of four viruses in the Northern Hemisphere vaccine that doctors and pharmacies are now pressing people to get may not be optimally protective this winter. Those two are influenza A/H3N2 and the influenza B/Victoria virus.

Credit CDC

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