Prediction of what goes into the yearly vaccine is about a year or more out from the flu season it gets administered in. To make the flu vaccine, the flu virus (or viruses, since the seasonal vaccine usually contains multiple strains) has to be cultured in millions of eggs, isolated, purified, combined, and turned into vaccine. It’s a very slow process.

This is one of the reasons that an mRNA vaccine for flu could be such a groundbreaker. The turnaround time is potentially much shorter.