How many male patients have been described as immune to quadrivalent HPV?
male refers to gender = 'M'; immune to quadrivalent HPV refers to immunizations.DESCRIPTION = 'HPV quadrivalent';
SELECT COUNT(DISTINCT T1.patient) FROM patients AS T1 INNER JOIN immunizations AS T2 ON T1.patient = T2.PATIENT WHERE T2.DESCRIPTION = 'HPV  quadrivalent' AND T1.gender = 'M'