A guess: The benefits of the vaccine to a 35 year old are substantially larger than to a 25 year old, and Moderna seems to provide better protection to new vari

A guess: The benefits of the vaccine to a 35 year old are substantially larger than to a 25 year old, and Moderna seems to provide better protection to new variants than Pfizer. This may be mostly just because the mRNA dose is larger in Moderna than Pfizer, but with a somewhat worse side-effect profile. In other words, if you have a medicine with both risks and benefits increasing with dose, the optimal dose will generally be larger for people who stand to benefit more.