Vaccines are THOROUGHLY Tested, Both Before and After Licensure

Anti-vaccination advocates often prey on the public’s lack of knowledge of medical science and the medical literature. This is never more apparent than when the anti-vaccination advocates claim that vaccines are not well-tested before they are used. For example, many anti-vaccination advocates present the following quote:1

“There has never been a single vaccine in this country that has ever been submitted to a controlled scientific study. They never took a group of 100 people who were candidates for a vaccine, gave 50 of them a vaccine and left the other 50 alone, and measured the outcome. And since that has never been done, that means if you want to be kind, you will call vaccines an unproven remedy. If you want to be accurate, you’ll call the people who give vaccines quacks.” –Robert S. Mendelsohn, M.D.

Now I honestly do not think that Dr. Mendelsohn actually said this, because I cannot imagine that a medical doctor could be this ignorant of his own field. Also, I have never seen a reference for this quote to something that Dr. Mendelsohn actually wrote. However, the point is clear. According to anti-vaccination advocates, vaccines are not tested before they are given to the general population.

Of course, as is the case with most of the claims made by anti-vaccination advocates, this could not be further from the truth! Before a vaccine can be licensed, it must go through several levels of controlled studies. First, it must be tested on animals. A group of animals is given the vaccine, and another group (the control group) is not. They are all then exposed to the germ that causes the disease. If the rate of the disease is significantly lower in the vaccinated animals than in the unvaccinated animals, and if there are no undesirable health effects in the vaccinated animals as compared to the unvaccinated animals, then the vaccine can be tested on human volunteers.

In the first level of human tests, a small group (usually less than 100) of volunteers are given the vaccine. If, over the next few months, there are no adverse effects noted in the small group compared to the population at large, then the vaccine can move on to the next level of clinical testing. In that level, a larger group (usually several hundred volunteers) is given the vaccine, and they are followed for up to two years. The rate of the disease in the testing group is compared to the rate for the nation as a whole. In addition, the rates of several health maladies in the testing group are compared to the rates of those maladies for the nation as a whole. If the rate of the disease is lower in the testing group as compared to the nation as a whole, and if the rates of the health maladies are no higher than the corresponding rates of the nation as a whole, then the vaccine is allowed to go to the final level of testing.

In the final level of testing, a huge group (typically several thousand) of volunteers is given the vaccine, and their health is tracked for several years. Once again, the incidence of the disease in the test group is compared to that of the nation as a whole, and the incidence of several health maladies in the test group are also compared to those of the nation as a whole. In order for the vaccine to be licensed, the rate of the disease against which the vaccine works must be significantly lower in the testing group than in the nation as a whole. In addition, the incidence of health maladies in the testing group must be no higher than that of the nation as a whole.

An example from history might help. The largest clinical study in the history of the United States was done on a vaccine. In 1954, the trial of the Salk polio vaccine was performed on 1.8 million children2. This trial was a double-blind, placebo-controlled study. In other words, half of the children got the vaccine, and the other half got the placebo. Until the end of the study, no one knew which children were which. In the end, the data indicated that the children who got the vaccine were significantly less likely to contract polio than those who got the placebo. In addition, the number of polio-unrelated illnesses were the same in the group of children who got the vaccine as compared to those who got the placebo. Thus, the vaccine was considered both safe and effective, and it was licensed for use.

In order to be licensed, every vaccine must go through not one, but at least two such trials, and that is after the vaccine has been tested on animals and tested on a small group of individuals mainly to judge its safety. Some vaccines do not make it. For example, doctors have tried to develop a vaccine against Respiratory Syncytial Virus (RSV) for years. It is one of the biggest killers of infants and young children in the U.S. There have been vaccines made, but they have never been approved for use, because the studies done on them demonstrate that they are not safe enough or effective enough to be considered a reliable medicine3,4.

That’s not even the end of the story. Not only must a vaccine pass through one level of animal study and three levels of human studies in order to be licensed, it is then continually monitored through the Vaccine Adverse Effects Reporting System (VAERS). This system is specifically designed to look for problems with vaccines, no matter how rare. For example, in 1999, the VAERS logged 15 serious bowel obstructions that occurred shortly after the rotavirus vaccine was administered. This frequency was quite low, since 1.5 MILLION doses of the vaccine had been given that year. Nevertheless, studies were done to see if those bowel obstructions were, in fact, related to the vaccine.

Several studies were done5, and the most thorough one demonstrated that there was a slightly elevated risk of serious bowel obstructions (one case in every 11,073 children vaccinated) for those who received the vaccine. Even though the risk is rare, the severity of the bowel obstruction combined with the low mortality of rotavirus in the United States led to the decision to pull the rotavirus vaccine from the standard vaccination schedule.

So you can see that vaccines, are rigorously tested before they are licensed for use, and then once they are licensed, they are continually monitored for safety. As the American Academy of Pediatrics says, “…vaccines are one of the safest forms of medicine ever developed.”6 The members of this academy ought to know. They have all spent several years studying medicine at the college and post-college level, and they have devoted their careers specifically to the health of children. To ignore their expertise would be quite foolish, especially in light of the fact that those encouraging you to do so must lie in order to make their case!


1. See, for example, The Pure Water Gazette or Dr. Jameson’s website (He is a popular chiropractor) or The Ptak Chiropractic Newsletter
2. Francis Jr T, et al. “An evaluation of the 1954 poliomyelitis vaccine trials: summary report.” Am J Public Health 1955; 45(suppl): 1-50.
3. Fulginiti VA, et al. “Respiratory virus immunization. A field trial of two inactivated respiratory virus vaccines: An aqueous trivalent parainfluenza virus vaccine and an alum-precipitated respiratory syncytial virus vaccine.” Am J Epidemiol 1969; 89: 435-448.
4. Chin J., Magoffin R.L., Shearer L.A., Schieble J.H., Lennette, E.H. “Field evaluation of a respiratory syncytial virus vaccine and a trivalent parainfluenza virus vaccine in a pediatric population.” Am J Epidemiol 89, 449-63 (1969)
5. Morbidity and Mortality Weekly Report, 48: 577; 1999
6. Samuel L. Katz, representing the American Academy of Pediatrics testimony before the Committee on Government Reform, U.S. House of Representatives, August 3, 1999 ( Available online)

Dr. Wile is not a medical doctor. He is a nuclear chemist. As a result, he does not dispense medical advice. He simply educates the public about scientific issues. Please consult a board-certified medical doctor before making any medical decisions for yourself or your family.