Originally Posted by genejockey

Which is why it's a hypothetical, because it's not possible to answer it yet. We'll know more in about 5 months.

We don't even know that there will be a need for more than a third shot. Most pediatric vaccines, there are several shots in the first couple years and none after that, but the protection lasts. And no, response doesn't diminish with subsequent vaccinations. It increases. That's why they do them that way. When we immunize mice to generate antibodies, we do it repeatedly over a number of weeks, and the antibody titer increases, and the antibodies being produced increase in affinity as the B-cells undergo somatic mutation, affinity maturation, and class switching.