Imputation
1 If S3BQ7 is missing and ever been vaccinated (S3BQ2) not equal to 1: Impute S3BQ7 by 0.
2 If S3BQ7 is missing and if for each vaccination since last 12 month is no, don't know and not applicable (S3BQ5 in 3 to 5): Impute S3BQ7 by 0.
3 If S3BQ7 is missing and if for each vaccination since last 12 month is not no, don't know and not applicable (S3BQ5 in 3 to 5): Impute S3BQ7 by median of S3BQ7 by Region.