28 October 2009

Polio vaccine (Salk)





The invention: Jonas Salk’s vaccine was the first that prevented polio,resulting in the virtual eradication of crippling polio epidemics.The people behind the invention:
Jonas Edward Salk (1914-1995), an American physician,
immunologist, and virologist
Thomas Francis, Jr. (1900-1969), an
American microbiologist
Cause for Celebration
Poliomyelitis (polio) is an infectious disease that can adversely
affect the central nervous system, causing paralysis and great muscle
wasting due to the destruction of motor neurons (nerve cells) in
the spinal cord. Epidemiologists believe that polio has existed since
ancient times, and evidence of its presence in Egypt, circa 1400 b.c.e.,
has been presented. Fortunately, the Salk vaccine and the later vaccine
developed by the American virologist Albert Bruce Sabin can
prevent the disease. Consequently, except in underdeveloped nations,
polio is rare. Moreover, although once a person develops polio,
there is still no cure for it, a large number of polio cases end without
paralysis or any observable effect.
Polio is often called “infantile paralysis.” This results from the
fact that it is seen most often in children. It is caused by a virus and
begins with body aches, a stiff neck, and other symptoms that are
very similar to those of a severe case of influenza. In some cases,
within two weeks after its onset, the course of polio begins to lead to
muscle wasting and paralysis.
On April 12, 1955, the world was thrilled with the announcement
that Jonas Edward Salk’s poliomyelitis vaccine could prevent the
disease. It was reported that schools were closed in celebration of
this event. Salk, the son of a New York City garment worker, has
since become one of the most well-known and publicly venerated
medical scientists in the world.
Vaccination is a method of disease prevention by immunization,
whereby a small amount of virus is injected into the body to prevent
a viral disease. The process depends on the production of antibodies
(body proteins that are specifically coded to prevent the disease
spread by the virus) in response to the vaccination. Vaccines are
made of weakened or killed virus preparations.
Electrifying Results
The Salk vaccine was produced in two steps. First, polio viruses
were grown in monkey kidney tissue cultures. These polio viruses
were then killed by treatment with the right amount of formaldehyde
to produce an effective vaccine. The killed-virus polio vaccine
was found to be safe and to cause the production of antibodies
against the disease, a sign that it should prevent polio.
In early 1952, Salk tested a prototype vaccine against Type I polio virus
on children who were afflicted with the disease and were thus
deemed safe from reinfection. This test showed that the vaccination greatly elevated the concentration of polio antibodies in these children.
On July 2, 1952, encouraged by these results, Salk vaccinated fortythree
children who had never had polio with vaccines against each of
the three virus types (Type I, Type II, and Type III). All inoculated children
produced high levels of polio antibodies, and none of them developed
the disease. Consequently, the vaccine appeared to be both safe in
humans and likely to become an effective public health tool.
In 1953, Salk reported these findings in the Journal of the American
Medical Association. In April, 1954, nationwide testing of the Salk
vaccine began, via the mass vaccination of American schoolchildren.
The results of the trial were electrifying. The vaccine was safe,
and it greatly reduced the incidence of the disease. In fact, it was estimated
that Salk’s vaccine gave schoolchildren 60 to 90 percent protection
against polio.
Salk was instantly praised. Then, however, several cases of polio
occurred as a consequence of the vaccine. Its use was immediately
suspended by the U.S. surgeon general, pending a complete examination.
Soon, it was evident that all the cases of vaccine-derived polio
were attributable to faulty batches of vaccine made by one
pharmaceutical company. Salk and his associates were in no way responsible
for the problem. Appropriate steps were taken to ensure
that such an error would not be repeated, and the Salk vaccine was
again released for use by the public.
Consequences
The first reports on the polio epidemic in the United States had
occurred on June 27, 1916, when one hundred residents of Brooklyn,
New York, were afflicted. Soon, the disease had spread. By August,
twenty-seven thousand people had developed polio. Nearly seven
thousand afflicted people died, and many survivors of the epidemic
were permanently paralyzed to varying extents. In New York City
alone, nine thousand people developed polio and two thousand
died. Chaos reigned as large numbers of terrified people attempted
to leave and were turned back by police. Smaller polio epidemics
occurred throughout the nation in the years that followed (for example,
the Catawba County, North Carolina, epidemic of 1944). A
particularly horrible aspect of polio was the fact that more than 70 percent of polio victims were small children. Adults caught it too;
the most famous of these adult polio victims was U.S. President
Franklin D. Roosevelt. There was no cure for the disease. The best
available treatment was physical therapy.
As of August, 1955, more than four million polio vaccines had
been given. The Salk vaccine appeared to work very well. There were
only half as many reported cases of polio in 1956 as there had been in
1955. It appeared that polio was being conquered. By 1957, the number
of cases reported nationwide had fallen below six thousand.
Thus, in two years, its incidence had dropped by about 80 percent.
This was very exciting, and soon other countries clamored for the
vaccine. By 1959, ninety other countries had been supplied with the
Salk vaccine.Worldwide, the disease was being eradicated. The introduction
of an oral polio vaccine by Albert Bruce Sabin supported
this progress.
Salk received many honors, including honorary degrees from
American and foreign universities, the LaskerAward, a Congressional
Medal for Distinguished Civilian Service, and membership in
the French Legion of Honor, yet he received neither the Nobel Prize
nor membership in the American National Academy of Sciences. It
is believed by many that this neglect was a result of the personal antagonism
of some of the members of the scientific community who
strongly disagreed with his theories of viral inactivation.

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