<prompt> In a epidemic of poliomyelitis, the best way to stop spread is by -Injection of killed vaccineOPV drops to all childrenIsolation of casesChlorination of all wells  <response>: - within an epidemic area, OPV should be provided for all persons over 6 weeks of age who have not been completely immunised or whose immune status is unknown. - OPV offers herd immunity and this propey is used in controlling epidemic. Reference : Parks textbook of preventive and social medicine, 23rd edition, pg no:208 p 