The fight against polio has its own vocabulary. Below are some of the most common terms and a brief explanation.
OPV: Oral polio vaccine. Made with live but weakened viruses. Cheap and delivered in drops that can be given by volunteers. But OPV viruses tend to mutate, potentially causing cases of VAPP and creating VDPVs (see below).
IPV: Injectable polio vaccine. Made with killed polioviruses. Doesn’t have the stability problem of OPV but is more expensive. Because it requires an injection, IPV must be given by trained medical personnel.
Wild Poliovirus: Polioviruses found in nature. The term “wild” is used by scientists to distinguish between natural viruses, viruses used in OPV and viruses that result from OPV use.
Sabin Strains: Also called vaccine viruses, these are the weakened viruses used in OPV production.
VDPVs: The acronym stands for vaccine-derived polioviruses. When Sabin strains spread from child to child, they mutate and can regain the power to paralyze. Scientists use the term VDPV to identify these viruses.
VAPP: Vaccine-associated paralytic polio, another unwanted byproduct of OPV use. Very rarely – once in about 750,000 OPV doses given – the live oral vaccine actually causes paralysis in the recipient or a close contact.