Polivirus is a more efficient transmitter, unlike other faeco-orally transmitted viruses. Therefore, naso-pharyngeal mucosal immunity and gut mucosal immunity may be important against poliovirus infection. I suspect that the mucosal immunity due to OPV is short-lived. Two doses do not provide sufficient mucosal immunity for interrupting transmission. I have changed the word strategy and replaced it with tactic.
Tactics can vary.
The vaccine may be OPV or IPV or a combination. We have, rightly or wrongly chosen OPV, for the time being. Pulse immunization with 3 doses rapidly shrinks the susceptible pool of children within the total pool of children. Such rapid shrinking results in break of transmission, rather like an epidemic which ends with no further cases because the susceptibles are exhausted or are too few and far betwen for transmission to reach them. If 3-dose pulse is done well, we should break transmission, no matter what the routine coverage has been.