The recent switch from the live, attenuated oral polio vaccine (OPV) to inactivated polio vaccine (IPV) has resulted in a collective sigh of parental relief.  After all, for many years, most of the cases of polio in the United States have been caused by the OPV.

But this relief ignores some of the history of the the polio vaccine, which includes occasional shifts between these two types of vaccines, due, at least in part, to concerns about both. 

And because of questionable statistical analysis, we may have been led to believe both IPV and OPV are safer than they really are.

There has long been a tug of war between these two kinds of polio vaccine. While there was always concern about using a live, albeit attenuated or weakened, virus, for many years it was widely thought that it inevitably conferred better protection, while at the same time being cheaper and easier to administer than an inactivated, or "killed", virus did.  Inactivated polio vaccine, however, was known not to cause polio and to be more stable.  (Vaccines, 1988, 1999) With the development of an "enhanced-potency inactivated poliovirus vaccine" in November 1987,  the apparent immunogenic advantage conferred by oral polio vaccine was lessened. (Pediatrics)

In 1936, the first polio vaccine, a live, attenuated one,  was tested, even though "The scientific base was woefully inadequate to justify human trials....Thousands of subjects received these vaccines, some of whom developed paralysis soon after inoculation, often in the inoculated limb. These findings raised the specter of persistence of live virulent virus in the vaccine, and the trials were terminated."  (Vaccines, 1988, 1999)

The Salk IPV came next, but the difficulty of controlling vaccine virulence became apparent once again, when in 1955, in what came to be known as "the Cutter incident", an improperly inactivated vaccine from one laboratory caused 260 cases of poliomyelitis, including 192 which were paralytic, before it was withdrawn.  That particular problem ended up being solved, but a few years later, right around the time the Sabin oral polio vaccine was introduced, it was found that both inactivated and live polio vaccine lots were contaminated with the SV40 virus.  In this case, however, vaccine stocks were not recalled.

(Current concern about thimerosal/mercury in vaccines demonstrates clearly that the question of the safety of biologicals used in vaccine production, including recognition and removal of contaminants, is not going to easily go away.)

And now, due to the apparent success of the polio vaccine and/or other factors, virtually all cases of polio in recent years in the United States, have been attributed to the live vaccine.  Consequently, in the United States the IPV is once again the vaccine of choice. 

In a study reported last year in Pediatrics, the journal of the American Academy of Pediatrics, a reassuring report was issued on the safety of IPV as compared to OPV. Among the conclusions drawn, was the following:  "In general, the annual reporting rates of events were similar for IPV and OPV, except for a somewhat higher rate of death after IPV than after OPV (0.83 versus 0.17 per 100,000) doses, and of nonfatal serious events (1.6 vs. 0.9 per 100,000 doses)  in 1998."

Unfortunately, there is reason to question this analysis, as well as some of the conclusions of the report.

First, the children included in this study received as many as the first two doses, so the number of children represented by these adverse reactions is somewhere between 50,000 and 100,000.  If more than one dose is given to children for whom adverse reactions are being reported, and the basis for determining the rate of reactions is doses, then the rate among children will be diluted, as appears to have occurred  in this case. 

Second, and as stated in the Pediatrics article, "Reporting rates must not be interpreted as incidence rates because of substantial underreporting." Credible estimates of the percent of adverse reactions that are reported range from 1-10%.  (While it is unknown exactly what percentage of serious vaccine reactions are reported, serious adverse drug reactions may well be as low as 1%.)

Here we are talking about actual numbers of children having a reaction, not the rate of reactions.  It means that all we actually know from the numbers reported in Pediatrics is that between 8.3/50,000-100,000  and 83/50,000-100,000  (or from 1 out of 602 to 1 out of 12,048) CHILDREN MAY HAVE DIED after IPV and that between 16 out of 50,000-100,000  and 160 out of 50,000-100,000  (or from 1 out of 313 to 1 out of 6,250) CHILDREN MAY HAVE HAD A SERIOUS REACTION after IPV.  Those are pretty big spreads.

Thus, there are only two things we know for sure: 1) that there is a clear-cut, unequivocal need to know how many children actually got those 100,000 doses and 2) that there is a clear-cut, unequivocal need to know how many adverse IPV-associated reactions really occurred.  Dose-dilution effects and under-reporting result in potentially significant underestimation of actual adverse reactions and adverse reaction rates.  Any statistics derived from such a base are meaningless at best, and misleading at worst..

The risks from OPV were probably similarly underestimated as well, given underreporting and the fact that those in the study who had received OPV had also received between one and two OPV doses. And while the implication of the reassurances about similarities between OPV and IPV in the Pediatrics article are that they are equally safe, the truth is, there are valid reasons to conclude they may be equally unsafe. 

In other words, both vaccines may well be causing far more damage than we have been told.  For instance, in 1998, combined OPV/IPV deaths reported in 1998 totaled 70.  (Pediatrics) If the more "conservative" estimate of 10% reporting is true, that would mean 700 polio vaccine-associated deaths occurred in the year 1998 alone.  At any rate, it would seem that considerably more deaths could be occurring than we are being made aware of.

What does seem clear from all this is that the discussion is no longer necessarily concerned with a small, almost insignificant number of possible deaths and other serious reactions.  

What are the real risks from OPV and IPV?

How do the real risks of getting paralytic polio or experiencing any other serious reactions as a result of OPV compare to the risks of death and other serious reactions from IPV? 

What would the benefit/risk ratio of administering polio vaccine be were the real risks to be determined, particularly given the fact that wild polio isn't thought to be circulating in the U.S.?

Why is there not a 100% effort to assure that 100% of vaccine-associated reactions get reported?  Isn't there a moral obligation to do so, given that these vaccines are not only recommended, but "mandated" for healthy infants and children?
 

Sandy Mintz