Polio vaccine example

A well-documented example of a vaccine-associated adverse reaction is vaccine associated paralytic poliomyelitis (VAPP). This is a very rare event that occurs in about two to four in every million doses of oral polio vaccine (OPV) given.²⁹ A live viral vaccine, OPV contains an attenuated (weakened) version of the disease-causing poliomyelitis virus. The vaccine is given orally and causes a mild infection that creates immunity against the wild poliovirus. However, in very rare instances, OPV can cause paralysis (VAPP), either in the vaccinated child, or in a close contact. VAPP can be proven by a laboratory test that detects vaccine virus in a clinical case of polio.

When there are cases of poliomyelitis in the population, the very rare risk of VAPP is very much less than the risk of acquiring polio by natural infection. However, in countries where there are no longer cases of wild polio, VAPP can become a greater risk than wild polio. In many countries where wild polio has been eliminated, programmes have switched to using inactivated (killed) polio vaccine (IPV), a more expensive vaccine that does not carry the risk of VAPP, but must be injected by a trained health worker.