double check equations used to calculate different VEs

[yangclaraliu]

• double check equations, but assuming correctly calculated VE_infection, VE_disease (incremental to infection), VE_hosp (incremental to infection) [optionally if empirically supportable: VE_icu (incremental to hosp)], VE_death (incremental to infection)

These calculations are done in: https://github.com/yangclaraliu/covid_vac_africa/blob/main/code/0_4_Vac_Char.R

the ve_i_o, ve_d_o, ve_h and ve_mort are based on observation in the existing literature.