Originally Posted by ma2two
Really? Are you sure about that?
What kinds of things do they use for the "placebos?" Do the tests show that the people getting the "placebos" get the disease at a higher rate? Can you provide links? These types of clinical trials don't last very long. So I don't see how, without purposely exposing the people to the disease, which they wouldn't be allowed to do, that they could determine the "unvaccinated" people get the disease more often.
Yes, I am sure about that. Here is a page that describes the vaccine development process and the phases of vaccine trials. As the page mentions, while the placebo can be something innocuous such as saline solution, often it is tested against another vaccine. I understand why people may object to this for safety testing since the other vaccine could be causing the same bad reactions, but when testing for efficacy, it doesn't really matter much whether the placebo is saline or the rabies vaccine unless we're going to consider that the rabies vaccine is magically protecting against HIV or some disease it wasn't designed to - extremely unlikely.
For very rare diseases such as tetanus and rabies, yes it would be hard to test them against natural exposure. I'm not sure how those are handled, but I'm guessing evidence supporting them relies mainly on animal tests, tests of antibodies after vaccination in humans, and long term observation of vaccinated populations. These are the only two vaccines I can think of off the top of my head for which this would be a problem. Oh, and smallpox vaccine, if they ever try to make a safer one.
For most vaccines though, the diseases were common enough pre-vaccine that reasonably large studies could have enough exposure to see a significant difference (or lack there of) of disease between the vaccinated group and the placebo group.
I am talking about vaccines for diseases not previously vaccinated for, by the way. A new measles vaccine would be tested against existing measles vaccine (still in double-blind tests) as it is considered unethical to give a placebo when there exists a vaccine known to be effective. There have been relatively recent tests of different measles vaccines in areas where measles is still endemic... there has also been a fair amount of controversy over at least one of these tests as the parents of children enrolled may not have been fully informed :( I think (but am not sure) that the procedure is also different for combination vaccines that combine vaccines that were already known to be effective rather than entirely new vaccines.
A few examples:
Here is a really long but interesting paper on the creation and testing of the Salk vaccine, including background information on polio and other vaccine attempts. Discussion of designing the trial begins on page 8, and description of the final design on page 13. There were over 450,000 children in the double-blind placebo study. There was also a non-blind study of over 560,000 children where 220,000 or so were given the vaccine and the rest served as controls. The results showed that while cases of polio still occurred in the vaccinated group, the rate of infection was less than half the rate of infection in both the placebo and the control group. Also, the disease was more severe in the control group - none of the vaccinated children died of polio, but there were fifteen fatal cases in the control groups. The numbers are at the bottom of page 19 & top of 20. The placebo used was a saline injection.
Here is a brief description of the random double blind trial for an HIV vaccine that unfortunately revealed that it was not effective.
Section 14 of this document describes pre-license trials of Rotarix.
The clinical evaluation section of this gives a brief description a double-blind placebo trial of a HIB vaccine and its results.
Abstract discussing a double blind trial of inactivated measles vaccine alone and inactivated measles vaccine + live measles vaccine against a placebo in the early '60s.
Zostavax package insert (shingles vaccine). Section 14, which begins near the bottom of page 8, outlines the clinical trials.
Prevnar7 package insert. Clinical evaluation begins on page 3. This one mentions that a MenC vaccine was used as the control in the US study and HepB vaccine in Finland.