question: Name the least age for the 1st dose for 3 doses of 2-3 drops
answer: SELECT minimum_age_at_1st_dose FROM table_name_28 WHERE number_of_doses = "3 doses" AND dose = "2-3 drops"
context: CREATE TABLE table_name_28 (minimum_age_at_1st_dose VARCHAR, number_of_doses VARCHAR, dose VARCHAR)