Yes, and we are also pretty certain that the mechanism of action is the number of mRNA particles contained: 30 µg for Pfizer/Biontech vs 100 µg for Moderna.

As a result, Germany e.g. uses half-doses for Moderna and vaccinates under 30s exclusively with Biontech.

Just to clarify: half-doses are only used for booster shots (following EMA recommendation). First and second shots still use full dosage.

That is correct, thanks for clarifying.