The experts are not randomly choosing strains. A few years ago it was 3 strains, they recently added a 4th. They could add a 5th next year, or drop back down to 3 depending on what they are seeing actually happen.
The real problem they have is the flu mutates. They know what strains they see now and can add them all easily enough. In the few months between deciding on strains and manufacturing them the flu can mutate to some new strain that wasn't even seen before.
The real problem they have is the flu mutates. They know what strains they see now and can add them all easily enough. In the few months between deciding on strains and manufacturing them the flu can mutate to some new strain that wasn't even seen before.