Polio vaccine: safety

So I have (slowly) been reading through Neil Miller’s book Vaccines: Are the Really Safe and Effective? As you can probably guess from the title and circumstances, the book is very skeptical about the utility of vaccines. In the last examination of this book, I tackled Miller’s assertion that the polio vaccine was not responsible for the decline of polio in the US. As a contrast, I presented the CDC(Centers for Disease Control) publication called the pink book, which gives the CDC’s version of the story. Both sources used different data for number of polio cases, and it was hard to reconcile them. A trip to the library to look at International Mortality Statistics is warranted, as soon as this full time employee and father of two can escape to the library for a little while. There is another worthwhile discussion, which I’m deferring, in the book which involves the redefinition of polio and the misclassification of other diseases with similar symptoms, such as aseptic meningitis.

Until then, I’ll move onto safety. Miller makes the assertion that Jonas Salk (yes, the leader of the project that lead to the original polio vaccine) testified that the live polio vaccine was essentially the sole cause of polio after 1961. The CDC’s position is that the last indigenous (i.e. wild-type polio virus) case was in 1979 (Miller states this and references The Poisoned Needle, but I got this statement out of the pink book as well). So I don’t think there’s an argument that the live/attenuated virus vaccine was the cause of some cases of polio. What is in question is whether the inactivated version causes polio. The CDC says no. Miller asserts yes, and quotes the CDC as saying that polio vaccine, including IPV(inactivated polio virus), can cause “serious problems or even death.” Here’s the Feb 2007 version (pdf) of the page Miller quotes. These words as quoted by Miller do appear on the page but out of context. Here’s a little more context:

However, a vaccine, like any medicine, could cause serious problems, such as a severe allergic reaction. The risk of a polio shot causing serious harm, or death, is extremely small.

So the CDC’s assertion is that the serious harm or death comes from severe allergic reactions, which can occur with any medication. It’s also worth noting that the CDC lists risk factors for the allergic reaction, and lists people who should avoid the vaccine or wait.

Conclusion for this section: Miller overstates the risk. I also think he took too many statements out of context to make his case.

Miller also talks about the SV-40 virus, which is a virus found in monkeys (SV stands for ‘simian virus’) and is speculated to cause cancer in humans. This agent was discovered in 1960 (or 1959 according to Miller), and was subsequently removed from vaccines. The CDC has a page on SV-40 here. Of course, the tone of the CDC’s FAQ is more muted than Miller’s assertions. Miller pretty much claims that SV-40 causes cancer, while the CDC says that there has been some mixed evidence for an association but that causation has not been conclusively proven. There are a few things I’ve noted here:

  • Miller asserts that “Despite official denials of any correlation between polio vaccines, SV-40 and increased cancer rates … .” He cites a press release by Barbara Fisher of the National Vaccine Information Center from 1998. However, the CDC’s page hardly constitutes an official denial of correlation. Perhaps the CDC changed their tune over the years, or Fisher was overreacting to the CDC’s muted tone.
  • The CDC notes that SV-40 does not have to come from contaminated vaccines, and that SV-40 has been found in humans who were not given contaminated vaccines.
  • I do think Miller brings up a great point: testing can only be done for known viruses, and we don’t know what else is out there. Our virus screening methods may still be imperfect.
  • Miller asserts that “Despite the polio vaccine’s long history of animal-virus contamination, today’s inactivated shot is manufactured in much the same way as earlier versions. …” To me, this statement carries the undertone that we are not learning from our mistakes and are pretty much marching forward with the same stupid strategy. However, I came to a different conclusion. While the basic ideas of modern polio vaccine production (which is the inactivated type, not the problematic live virus type) are the same, the differences seem to be pretty important.

Conclusion: Miller brings up good points, but overstates his case. The CDC’s tone is much more muted, and acknowledges most of Miller’s basic points.

Finally, Miller discusses the theory that HIV was taken from monkeys to humans via the polio vaccine. In short, to me it sounds like he’s blaming the AIDS epidemic on polio vaccines.

The CDC’s position is, well, let’s quote:

The suggestion that human immunodeficiency virus (HIV), the AIDS virus, originated as a result of inadvertent innoculation of an HIV-like virus present in monkey kidney cell cultures used to prepare polio vaccine is one of a number of unsubstantiated hypotheses.

The weight of scientific evidence does not support this idea and there is no more reason to believe this hypothesis than many other which have been considered and rejected on scientific grounds.

Since the 1960’s, billion of doses of oral polio vaccine have been delivered worldwide and no association with HIV infection has ever been recorded.

I guess the CDC does not agree at all with Miller’s assertion. An additional page with an FAQ and references discusses origins of the polio vaccine and AIDS theory and evidence why the link, if it exists at all, is weak. Of note, Miller’s support of the polio vaccine-AIDS theory is pretty weak and mostly circumstantial, and most of the expert statements he references comes in the early 1990s when the issue was not really resolved. It seems that the consensus against such a link came in 2001.

Conclusions: I find Miller’s evidence unconvincing. I have not evaluated the CDC’s evidence in as much detail, but what I have evaluated is more convincing than Miller’s.

Finally, Miller makes the worrying assertion that polio vaccines are contributing to new and more virulent strains of polio. This is a point that every public health official needs to consider with any vaccine, i.e. are we making the problem worse. I must admit that I haven’t evaluated the assertion in detail, but I’ve browsed through the global polio eradication site, and the evidence from other countries is not there to convincingly back this assertion up.

Overall conclusion on polio vaccine safety: Miller wildly overstates his case. The modern polio vaccine is a lot safer than Miller’s missive would otherwise suggest.  Prior version of polio vaccine had some problems, which have been fixed. However, he does bring up some questions that deserve more attention. I also find the CDC’s information fairly credible, even if its tone is usually muted.

Previous articles in this series:


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