Contact immunity

The potential for contact immunity exists primarily in "live" or attenuated vaccines.

However, the live virus multiplies briefly, may be shed in body fluids or excrement, and can be contracted by another person.

[1] Although contact immunity is an advantage of OPV, the risk of vaccine-associated paralytic poliomyelitis—affecting 1 child per 2.4 million OPV doses administered—led the Centers for Disease Control and Prevention (CDC) to cease recommending its use in the US as of January 1, 2010, in favor of inactivated poliovirus vaccine (IPV).

The CDC continues to recommend OPV over IPV for global polio eradication activities.

In the case of OPV, an average of eight to nine adults contracted paralytic polio from contact with a recently immunized child each year.