IV.

Disease Control

Three broad types of the virus have been identified: the Brunhilde (type 1), Lansing (type 2), and Leon (type 3) strains. Immunity to one strain does not furnish protection against the other two.

Poliomyelitis control was made possible when, in 1949, the bacteriologist John Franklin Enders and his co-workers discovered a method of growing the viruses on tissue in the laboratory. Applying this technique, the doctor and epidemiologist Jonas Salk developed a vaccine prepared from inactivated poliomyelitis viruses of the three known types. After field trials in 1954 the vaccine was pronounced safe and effective, and mass inoculation began. The virologist Albert Sabin subsequently developed a vaccine containing attenuated, live polio virus that could be given orally. This vaccine, called trivalent oral polio vaccine (TOPV), was licensed in 1963 and has replaced the Salk injectable vaccine as the standard immunizing agent in the United States and elsewhere. As a result of routine immunization, outbreaks of paralytic poliomyelitis declined dramatically from 57,879 cases in the United States in 1952 to only a few each year.

The vulnerability of a population that was not immunized was demonstrated in 1979, when 16 cases of paralytic poliomyelitis occurred among Amish people in the United States and Canada who had not been vaccinated.

In 1988, when 350,000 cases of poliomyelitis were reported worldwide, the World Health Organization (WHO) launched a global immunization programme. By early 2001 the campaign had succeeded in reducing the incidence of the disease by 99 per cent, with only 3,500 cases being recorded in 2000. As of 2002 poliomyelitis had been officially declared eradicated from Europe, the Americas, and a number of Pacific Rim nations. WHO’s target date for poliomyelitis to be eradicated from the entire world is 2008.