Reports from the leaders in the polio vaccine field that the treatment is safe, efficient and potent marks another great advance in medical science. Dr Thomas Francis Jr, who handled the statistics on the tests of last year, found the vaccine 80 to 90 percent effective on the basis of the tests. Dr JE Salk, for whom it is named, thinks it can be 100 percent effective when properly administered and handled it in shipment.
The report is filled with good news for the nation. One of the most encouraging statements is the fact it is extremely effective with bulbar polio, the most dangerous type. And the reactions among thousands of children have been minor. Only a fraction of one percent had any reaction. Major reactions were rare, and could not be traced directly to the vaccine, in most cases.
While the vaccine is thought to be effective only for about five months, booster shots may be taken to extend the effectiveness. But the five months will bridge the spring and early fall periods when polio seems to strike hardest.
While the remarkable tests have opened a great new field in medicine, there still is much to be learned in the opinion of Dr Salk. He wants to know more about the proper spacing of shots. The fact that many children were given dummy shots in order to get a pattern of infection in some areas, while others had the real vaccine, apparently proved a valuable part of the experiment.
On the question of safety, Dr Francis said 931 children who were vaccinated and 939 given dummy shots had minor reactions, each the same percentage, .04.
Of the so called “major” reactions, none could clearly be attributed to inoculation. There were nine in children receiving the vaccine, and 13 such reactions those getting dummy shots. These finding failed to implicate the vaccine as a significant cause of untoward reactions. There was no evidence to blame the vaccine as a source of infection, the report declared.
Among children who developed paralysis, there was no evidence that the paralysis localized or involved the left arm where all injections were given.
Dr Francis said in the dummy-vaccine shot areas, the Salk vaccine was 68 percent effective against Type 1, 100 percent against Type 2, and 92 percent against Type 3.
“This clearly agrees with previous demonstrations that most lots of vaccine varied considerably as measured by the occurrence of polio,” Dr Francis said. He said it is not possible to give a single figure expressing the numerical or percentage effectiveness of the vaccine in a complete sense.
Dr Francis said there was no significant difference in the rates of non-paralytic polio in test and control groups.
Bulbar polio and spinal paralytic polio
Against bulbar polio, the vaccine was estimated to have been from 81 to 94 percent effective in preventing paralysis in the dummy shot control areas. The effect was less striking in spinal paralytic polio. About 60 percent down to a lower limit of 39 percent. From limited numbers of children tested in Canada and Finland, the vaccine also was credited with showing a significant effect.
Dr Salk declared the first two shots stimulate the production of antibodies in the blood stream and the child develops a state of readiness to make antibodies. His antibody producing system becomes like a cocked revolver. The booster shot given at least seven months later serves as a trigger to produce remarkably high amounts of antibodies.
He said natural exposure to polio, if it occurs after the first two shots, also acts as a trigger to explode the antibody mechanism into action.
Dr Salk said the amount of antibodies induced by the seven to eight months spacing of the shots is higher than that brought about by paralytic infection itself.
Some batches of vaccine used in the tests were overtreated with a preservative chemical, which in effect “fried” the dead virus, so much that it lost ability to stimulate antibodies, Dr Salk said.
Dr Salk declared last year’s study was a test of whether a “primary vaccination (three shots spaced in five weeks)” alone could prevent paralytic polio rather than a test of the effectiveness of what he called a full immunization by spacing the shots over a much longer period.
Thus, approximately two decades of effort by the National Infantile Paralysis Foundation has paid grand dividends. To the millions of people who have participated in the annual March of Dimes campaigns, goes a great deal of credit for financing the extensive research. And to the medical profession goes much more credit for keeping at what at times seemed an almost hopeless assignment.
When sufficient additional tests and refinements have been made, the medical profession will be ready to fully advise us on how the remarkable vaccine should be handled. Meanwhile, there appears to be every assurance that we have developed protection against one of the most dangerous of diseases.