If smallpox ever should get back out into the environment, the results could be devastating because smallpox vaccination is no longer given and so the population fully susceptible to the disease grows year by year. A program to try to eliminate polio from the world is now underway. Except for cases caused by OPV, the disease has now been eliminated from the Western hemisphere. Outbreaks of polio still occur in Africa, the Indian subcontinent, and parts of the Near East. One problem is that experimental vaccines often elicit an immune response that does not actually protect against the disease.
Most vaccines preferentially induce the formation of antibodies rather than cell-mediated immunity .
But viruses are intracellular parasites, out of the reach of antibodies while they reside within their target cells. Antibodies may have a role in preventing infection or minimizing its spread, but cell-mediated responses will probably turn out to be far more important. The DNA is incorporated in a plasmid , which is then injected into a muscle just as conventional vaccines are. The plasmid is taken up by cells. The gene encoding the antigen is transcribed and translated.