I really don't understand where this idea of "annual boosters" is coming from. SARS-CoV2 is clearly on the trajectory to become one of the many viruses that are endemic in humans. This means that everyone will occasionally get exposed to it which updates the immune memory. The question is how to get there while minimizing the damage to the population. The mRNA vaccines were originally tested with two doses which appears to provide a strong and relatively long lasting protection against severe disease. Now it turned out that giving a third dose after a few months improves the protection even more, which is particularly relevant for high-risk patients.