That's why they are either limited or outright banned for certain populations.
Moderna remains banned in the Nordics for boys/men under 30. NHS does NOT give AZ boosters, only mRNA. NHS will not give AZ for those under 40, only mRNA.
Follow the science below:
[1] https://thl.fi/en/web/infectious-diseases-and-vaccinations/w...
[2] https://www.nhs.uk/conditions/coronavirus-covid-19/coronavir...