Oral polio vaccine is highly effective and inexpensive (about US$0.10 per dose, or US$0.30 per child and its availability has bolstered efforts to eradicate polio. A study carried out in an isolated Eskimo village showed that antibodies produced from subclinical wild virus infection persisted for at least 40 years. Because the immune response to oral polio vaccine is very similar to natural polio infection, it is expected that oral polio vaccination provides similar lifelong immunity to the virus.
Contact immunity to polio can occur when attenuated poliovirus derived from the oral polio vaccine is excreted, and infects and indirectly vaccinates unvaccinated individuals.
Errors can occur when the chromosomes segregate into the gametes during meiosis resulting in egg or sperm with too many or too few chromosomes. As a result, fertilised eggs and the ensuing embryos may have trisomy (an extra chromosome of a particular pair) in each cell or monosomy (one chromosome fewer in each cell).
