Thank you for your comment and I am sorry for my late response. That's an interesting idea - for girls to get smaller vaccine doses. So far, I'm not aware of any study that has investigated this.

However, a few experts have considered smaller Covid-19 vaccine doses for women back in 2021 (link below). But there seems to be no update on this matter.

https://www.nextavenue.org/covid-vaccine-women-side-effects/

Notably, it's not only vaccine responses that are stronger with X chromosomes but drug responses as well. Drug side effects tend to affect women more than men, unfortunately.