Question: How many patients with 'allergy to eggs' have been immunized with 'Td (adult) preservative free'?
SQL: SELECT COUNT(DISTINCT T2.patient) FROM allergies AS T1 INNER JOIN patients AS T2 ON T1.PATIENT = T2.patient INNER JOIN immunizations AS T3 ON T2.patient = T3.PATIENT WHERE T1.DESCRIPTION = 'Allergy to eggs' AND T3.DESCRIPTION = 'Td (adult) preservative free'