Derivation
variable: meas2date (table[s]: all_vaccination_records [derived table])
variable: birth_date (table[s]: all_vaccination_records [derived table])
*for MEAS2: problem if vacc date is before first dose (supposed to be after 1st dose)
if "`vacc'"=="meas2" replace `vacc'Sprob=1 if (meas2date<meas1date | meas1date==.) & meas2date~=. & birth_date~=.