> flu vaccines are based on weakened viral particles, not mRNA transcriptions of key viral proteins
Thankfully this is changing. Moderna is entering trials for an mRNA vaccine for seasonal flu. The faster development time for mRNA vaccines will mean more time to study the emerging flu strains before committing to which to include in the booster.
The flu booster shot is actually a full vaccination based on the leading 2-3 variants they predict will be dominant in the coming flu season.
Also, flu vaccines are based on weakened viral particles, not mRNA transcriptions of key viral proteins... so the two really aren't comparable.