This PR includes 3 big upgrades to the vaccine model:
Strain aware - the vaccine is now strain aware and different levels of efficacy can be applied to different strains
Immunity model - the immunity is now extended to 3 levels: full protection, protection against symptoms, protection against severe disease
Vaccine conveyed immunity - instead of 2 types of vaccine either conveying full or against symptoms, each vaccine can convey each of the 3 types of immunity with different levels of efficacy
This PR includes 3 big upgrades to the vaccine model: