Polio Disease and Poliovirus
There are three wild types of poliovirus (WPV) – type 1, type 2, and type 3. People need to be protected against all three types of the virus in order to prevent polio disease and the polio vaccination is the best protection. There are two vaccines used to protect against polio disease, oral polio vaccine and inactivated poliovirus vaccine.
The oral polio vaccine (OPV) is used in many countries to protect against polio disease and has been essential to the eradication effort. People who receive OPV may shed the virus and can infect others, especially those who are not vaccinated. In areas with low vaccination rates, the OPV virus can continue to infect new individuals. In rare cases, the OPV virus can accumulate changes over time and become like wild poliovirus (WPV). These new viruses are called vaccine-derived polioviruses (VDPV) and can cause polio disease.
After wild poliovirus type 2 was declared eradicated in 2015, the world switched from trivalent to bivalent OPV. Trivalent OPV contains all three types of poliovirus, while bivalent OPV only contains poliovirus type 1 and 3. This switch means that OPV no longer protects against WPV2.
Inactivated poliovirus vaccine (IPV) protects people against all three types of poliovirus. IPV does not contain live virus, so people who receive this vaccine do not shed the virus and cannot infect others and the vaccine cannot cause disease. Countries that use bOPV have added a single dose of IPV to protect against WPV2.
Poliovirus containment is currently focused on WPV2 because it was officially declared eradicated in 2015. Containment measurespdf iconexternal icon are being put in place for laboratories or other facilities that handle or store the virus.