National immunization days: state of the art.

National immunization days (NIDs) are nationwide mass campaigns to deliver supplemental doses of oral poliovirus vaccine to interrupt the circulation of wild polioviruses. They constitute one of the critical strategies for global poliomyelitis eradication and should be implemented in all countries with widespread poliovirus transmission. The certification of wild poliovirus eradication from the Western Hemisphere in September 1994 verified the effectiveness of this aspect of the World Health Organization's (WHO) overall strategy for polio eradication by the year 2000. NIDs require careful advanced planning and orchestration by each country. WHO provides specific guidelines for NIDs regarding the season, target age group, duration, frequency, inclusion of other interventions, vaccine delivery strategies, and evaluation. With strong routine immunization programs and the effective implementation of NIDs, "mop-up" campaigns, and acute flaccid paralysis surveillance, the goal of global polio eradication will be achieved.