Usually the base is living children with health cards seen by the interviewer (H1 = 1), but in countries where the respondent reported whether the child had received the vaccination for each vaccination the base is all living children.
Whether a date of vaccination was recorded on the health card for Polio 0 (at birth). Code 1 means the child has a date recorded for the vaccination. In some countries code 2 is used to indicate that the respondent reported that the child had received the vaccination although the health card was not seen or did not exist. This is done in countries where the respondent was asked if the child had received each individual vaccination when the health card was not available.