Since the 1930’s, the whole-cell pertussis vaccine began helping to prevent horrific and deadly cases of pertussis (whooping cough) that were violently killing about 8000 Americans every year, mostly babies and young children. The whole-cell Pertussis vaccine was replaced with the “acellular” version completely in the US and many other developed nations by the early 2000’s, but is still used in many developing nations. (Both the whole-cell and acelluar versions are administered in combination with the diphtheria and tetanus vaccines.)
The whole-cell vaccine worked very well, but it sometimes caused short-term yet very frightening side-effects, like sudden limpness or convulsions from fever. This led many to suspect, or insist, that it also was causing complex recurring seizures and acute or chronic encephalopathy (a brain disfunction or disorder). As fear led many parents to stop vaccinating their children, outbreaks began to come back, and some babies began to suffer and die again. This trend is continuing today.
The Institute of Medicine (IOM) was charged in 1991 with figuring out if the scientific evidence supported that suspicion or not. Regarding encephalopathy and related disorders (encephalitis or encephalomyelitis), they concluded that “the evidence is consistent with a causal relation between DPT vaccine and acute (temporary) encephalopathy” .
I am guessing that this sounded terrifying to many parents, as the conclusion of “consistent with a causal relationship” sounds definitive. But if you examine their categorization, it means that the evidence for this being a true vaccine reaction was not persuasive enough to conclude that “the evidence indicates a causal relation.” The evidence was suggestive enough, however, to stop short of saying the “evidence does not indicate a causal relation.” In other words, it might be causal.
How often might the pertussis vaccine cause acute encephalopathy? The IOM reported that the weight of the available evidence at the time was consistent with the findings of a fairly large study (the NCES) that had calculated a possible excess risk of acute encephalopathy due to pertussis vaccination in the range of zero to 10.5 cases per million doses of DTP. This should have been somewhat reassuring: if the DTP did cause acute encephalopathy, it was rare, possibly even zero.
Regarding “chronic” encephalopathy, which can be long-term and sometimes deadly, the IOM committee decided in 1991 that “there is insufficient evidence to indicate a causal relation between DPT vaccine and permanent neurologic damage.” But later, in 1994, after reviewing new NCES data, the IOM acknowledged that acute encephalopathy can sometimes lead to chronic neurologic dysfunction, including death, and so, the same conclusion they reached in 1991 about acute encephalopathy would apply to chronic illness/death provided that it followed an acute reaction occurring within 7 days of vaccination. They caution against people reading too much into their conclusion. They reported:
The committee concludes that the balance of evidence is consistent with a causal relation between DPT and the forms of chronic nervous system dysfunction described in the NCES in those children who experience a serious acute neurologic illness within 7 days after receiving DPT vaccine. This serious acute neurologic response to DPT is a rare event. The estimated excess risk ranged from 0 to 10.5 per million immunizations (IOM, 1991). The committee stresses that this is not the strongest statement regarding causality; the evidence does not “establish” or “prove” a causal relation. (bold mine)
Subsequent studies have been more reassuring about both the whole cell DTwP, as well as the MMR vaccine.
After the IOM’s maybe/maybe not conclusions in 1991 and 1994, some good evidence began to cast doubt on the suspicion that the whole cell pertussis vaccine, as well as the MMR vaccine, was causing brain disorders such as autism or complex seizures and acute or chronic encephalopathy.
Regarding autism, overwhelming scientific evidence has been building over the years that vaccines, in particular the MMR vaccine and those containing Thimerosal — a mercury based preservative used in some other childhood vaccines, but since removed for the most part anyway — are not responsible for autism as some had insisted and many feared. The IOM systematically reviewed the evidence on this question in 2004 and concluded the evidence favors rejection of a causal relationship to autism after reviewing the evidence on both sides of the debate.
I see a study published in 2001 was conducted by the CDC’s Vaccine Safety Datalink (VSD) Working Group to evaluate the risk of a “first seizure, subsequent seizures, and neurodevelopmental disability following the administration of diphtheria and tetanus toxoids and whole-cell pertussis (DTP) vaccine and measles, mumps, and rubella (MMR) vaccine.” The title of the abstract summarizes their conclusions: “Increased Risk of Seizures Following DTP and MMR Vaccine Is Not Associated with Any Long-Term Adverse Consequences.”
And, I see a very large Kaiser Permanente Vaccine Safety study, published in 2006, of 2 million children on the DTwP and the MMR vaccine that found no evidence for a causal relationship to encephalopathy or related disorders: “Encephalopathy after whole-cell pertussis or measles vaccination: lack of evidence for a causal association in a retrospective case-control study,” Ray P, et al.
Further, an intriguing 2006 preliminary study discovered that most presumed vaccine induced encephalopathy cases among a small sample were actually caused by a hereditary epilepsy-inducing genetic mutation, misattributed to a vaccination that happened to occur beforehand (temporally). Read: “De-novo mutations of the sodium channel gene SCN1A in alleged vaccine encephalopathy: a retrospective study,” Berkovic SF, et al.
Putting this important finding in the context of vaccination hesitancy and refusal, read this 2007 commentary, “Vaccines, Encephalopathies, and Mutations” by Anne T Berg, PhD and this 2008 commentary,“Genetics and the myth of vaccine encephalopathy” by Asif Doja, MD.
(There may be many other studies on this too, but I’ll stop here, for now.)
RECOMMENDED reading on this topic: “BRIAN DEER: THE VANISHING VICTIMS – Can whooping cough jabs cause brain damage in children? BRIAN DEER INVESTIGATES” The Sunday Times Magazine, November 1 1998. (Note: Brian Deer is the same investigative reporter who brought us the inside scoop on the Andrew Wakefield’s MMR vaccine-autism scare.)
Also, see my related post, “Serious disease risk vs. serious vaccine risks“