Why is full cell/high antigen dose pertussis vaccine dangerous for adults?
It seems it is not about pertussis.

I have found information in the Infanrix-DTPa characteristic that it is not recommended for adults due to high dose of diphteria toxoid.

Both Infanrix-DTPa and whole-cell DTP vaccines contain over 30 international units (whatever it is) of diphteria toxoid while Boostrix contains "not less than 2 i.u.".