<prompt> About herd immunity, all are true exceptDepends on clinical and subclinical casesInfluenced by immunizationDepends on the presence of alternative hostHerd immunity is constant  <response>: Elements which contribute to herd immunity are occurrence of clinical and subclinical infection in the herd immunization of the herd herd structure Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 110 