But it’s still hard to predict which forms of the virus will be spreading six months in the future. International travel complicates the process, allowing strains of virus to jump thousands of miles in hours.
“Those patterns really affect the flu season in some ways,” Blackman said. “We’ve wondered sometimes if we might not just end up with a 12-month-a-year flu issue. ... People travel all the time.”
The CDC’s conclusions about the coming season are provided to vaccine manufacturers. If the CDC predicts correctly, the vaccine matches the prevalent viruses. This year, it does, according to the latest CDC report.