OPV is highly effective against all three types of wild poliovirus. When this vaccine is used however, there is competition among the three viruses to cause immunity, which results in protection but not with equal efficiency for each type: it is most effective against type 2.
One dose of OPV produces immunity to all three poliovirus serotypes in approximately 50% of recipients. Three doses produce immunity in more than 95% of recipients. Immunity is long-lasting and probably life-long.
In most countries, OPV remains the vaccine of choice in routine immunization schedules and supplementary immunization activities.
Where more than one type of wild poliovirus is circulating, OPV is epidemiologically and operationally the best vaccine to use because protection develops to each of the three types of polio virus.