CNS Occasional Papers: #9

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Commentary

by Dr. D. A. Henderson


Dr. Zelicoff's analysis of the Aralsk outbreak and interpretation of the findings are regrettably flawed. Had his report been presented in an appropriate venue with suitable discussion, I believe it could have been seen in appropriate perspective. Unfortunately, it appears to have been presented with media coverage in mind. While he couches his summary conclusions in terms of "unanswered questions," he leaves little doubt as to his beliefs:

The answers to these and many other questions will almost certainly have a profound effect on civilian and military biodefense efforts... (O)ur complete reliance on a single vaccine (unmodified vaccinia) represents a serious potential vulnerability. Only a detailed analysis of the Aralsk strain with the most modern tools of molecular biology can guide public health officials and defense planners in formulating appropriate polices and prophylaxis which may include a concerted effort to produce new vaccines based on entirely novel approaches, along with testing of anti-viral drugs in animal models.

The report reveals that a hitherto publicly unknown outbreak of 10 smallpox cases occurred in Aralsk and that infection of the single index case possibly resulted from exposure to aerosolized smallpox virus from the Vozrozhdeniye Island test site in the Aral Sea. These findings are of interest but hardly dramatic or unexpected. Does the outbreak provide information that should heighten our concern or alarm? If there is something there, I cannot identify it.

Have we been aware that the Soviets worked to prepare smallpox virus as a biological weapon? Yes. Alibek has been quite explicit about this.

Have we been aware that an aerosolized preparation of smallpox virus can infect at a distance and at low dosage? Studies during the 1960s in England and the U.S. document the survival of vaccinia as a fine particle aerosol. The 1970 Meschede, Germany, outbreak provides better and more ample illustrative documentation of the potential of a smallpox aerosol.

Have we been aware that the Soviets performed tests of smallpox aerosols? Again, Alibek has been quite specific in telling us this. Further, former Vice-Minister of Health Burgasov, as quoted in a November 2001 Moscow newspaper article, stated that there had been an outbreak in Aralsk related to testing on the island.

Could this be an especially engineered, more virulent strain of smallpox? The only case apparently resulting from exposure to the aerosol was a 24-year-old woman whose rash was sufficiently atypical as not to be recognized as smallpox. Dr. Zelicoff indicates her onset to have been August 11 but, interestingly, as he points out, she recovered so quickly that she left Aralsk 4 days later to get married. This case would not appear to qualify even as "ordinary" smallpox. Meanwhile, none of her shipmates became ill according to Dr. Zelicoff. This is difficult to explain if the virus was indeed more virulent than normal strains and capable of evading the immune protection provided by ordinary vaccinia.

If this were an especially virulent virus, one might have anticipated that a hemorrhagic case might have given rise to other cases but not one of the three did so. Rao (1972), in has classic book on smallpox, points out that in his series of 385 cases of hemorrhagic smallpox, not once did a second hemorrhagic case occur among contacts of a patient with the hemorrhagic form. In other words, the Aralsk transmission pattern was not unexpected.

That 3 of the 10 cases were hemorrhagic is higher than usual but how much can be said with such small numbers. Two points are to be made: first, that the manifestation of hemorrhage is thought to relate to host factors rather than to the virus per se and, second, variation in the frequency of hemorrhagic cases varied widely from outbreak to outbreak. Rao found that of 85 hemorrhagic cases occurring among unvaccinated persons, 24 (28%) were 0-4 years of age (a more detailed breakdown by age is not provided) and 18 (21%) were in the 20-24 year age group. These were the highest numbers for any of the 5-year age groups and, interestingly, the deaths in the Aralsk outbreak corresponded with this distribution.

Is there evidence of resistance to the immunity provided by the vaccine? The answer is an unequivocal "no". Dr. Zelicoff expresses concern that all 7 patients who recovered had all been previously vaccinated. Five of the seven were 24 years of age and older (24, 33, 36, 38 and 60). Note that all 7 are recorded as having been vaccinated only once and that in childhood. No mention is made as to whether any had a vaccination scar as evidence of having been successfully vaccinated. From Jenner's time, it has been recognized that a single vaccination does not provide lifetime immunity. Dr. Zelicoff's assertion that "the efficacy of the smallpox vaccine is usually described as being in excess of 90 percent" may be correct for the first several years after vaccination but the protection afforded by a single inoculation wanes over time. After 20 to 30 years, protection against infection is minimal. In a country that was quite rigorous in enforcing vaccination, is it surprising that most of the cases had once been vaccinated?

Summary: This interesting smallpox outbreak provides further documentation that the Soviets were actively engaged in developing the smallpox virus as a biological weapon. There is nothing in the report to suggest that the strain used was either more virulent than other south Asia strains and certainly nothing that suggests that it resisted the immunity provided by conventional vaccinia infection.

Reference

Rao, A.R. (1972) Smallpox, The Kothari Book Depot, Bombay.


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