Friday, February 7, 2014

Re-Emerging Monkeypox: Why Smallpox vaccination policy is important to global health security

"Studies on the burden of human monkeypox in the Democratic Republic of the Congo (DRC) were last conducted in 1981 to 1986. Since then, the population that is immunologically naive to orthopoxviruses has increased significantly due to cessation of smallpox vaccination campaigns." See: Proceedings of the National Academy of Sciences of the United States of America http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2941342/  




 "After smallpox eradication, surveillance for human monkeypox from 1981 to 1986 in the DRC indentified 338 cases (67% confirmed by virus culture). The case fatality rate was 9.8% for persons not vaccinated with vaccinia (smallpox) vaccine, which was about 85% efficacious in preventing human monekypox (3,7). The secondary attack rate in unvaccinated household members was 9.3% ,and 28% of ase patients reported an exposure to another case-patient during the incubation period. Transmission chains beyond secondary were rare (8,9). A mathematical model to assess the potential for monkeypox to spread to assess the potential for monkeypox to spread in susceptible populations after cessation of vaccinia vaccination indicated that person to person transmission would not sustain monkeypox in humans without repeated reintroduction of the virus from the wild (7). See:http://wwwnc.cdc.gov/eid/article/7/3/01-7311_article.htm

While the eradication of smallpox, the first human disease to ever have been eradicated is a remarkable achievement by the Wolrd Health Organization (WHO), ushering an end to global smallpox vaccination, should we reconsider vaccination strategies in light of emerging and re-emerging disease, the threat perhaps posed by biological warfare/terrorism, coupled with advances in the life sciences which might create novel or even synthetic variants? Surely some herd immunity is better than none. To this end several Eurpean states have vaccinated health care workers, first responders and sections of their military personal, keeping in line with the United States strategies. In an abstract published in the US National Library of Medicine National Institutes of Health, entitled: Human Monkeypox: an emerging zoonotic disease, the authors, Parker S., Nuara A, Buller RM and Schultz DA, state: As a zoonotic agent, monkeypox virus is far less sensitive to typical eradicaiton measures since it is maintained in  wild-animal populations. Moreover, human vaccination is becoming a less viable option to control poxvirus infections in today's increasingly immunocompromised population, particularly with the emergence of HIV in sbu-Saharan Africa. An increased frequency of human monkeypox virus infections, especially in immunocompromised individuals, may permit monkeypox virus to evolve and maintain itself independently in human populations. See: http://www.ncbi.nlm.nih.gov/pubmed/17661673

The issue of re-introducing global smallpox vaccination is not a minor one, in light of increasing immunocompromised populations which did not exist prior to cessation of mass vaccination campaigns. People with certain immunodeficiency disorders are at a greater risk for serious side-effects from smallpox vaccination called progressive vaccinia (PV). In PV, the site of vaccinaiton does not heal; instead there is a progressive lesion at the injection site and eventual spread of the virus to other parts of the body, which, if not stopped by medical intervention eventually results in death. People with PV have traditionally been treated with vaccinia immune globulin (VIG). VIG is a product made from antibodies obtained from people previously immunized with the smallpox vacine. See: http://www.fda.gov/BiologicsBloodVaccines/ScienceResearch/ucm295240.htm

While global smallpox vaccination due to the potential increase in monkeypox in quite localized geographic populations does not appear at this time to be merited, additional issues encourage us to keep an open mind. It is estimated that at least four nations retained smallpox stocks after eradication, exluding the two official repositories maintained at Vector in Novosibirsk and CDC in Atlanta. Moreove, rapid advances in the life sciences could introduce modifications as was the case with regard to smallpox and the former Soviet Bio-preparat program.  In 1971, a Soviet field test at Aralsk-7, on Vozrohdeniya Island caused an outbreak of smallpox. The Soviet scientists involved had isolated a particularly virulent stain called India 1967 or India -1 as it is referred to today. As the name suggests, it was brougt back from India in 1967 by a special Soviet medical team, sent to India to help eradicate the virus. By the mid-1970's the Soviet's were producing and weaponizing 20 tonnes of India per year. This strain is considered to be the most likely one terrorist or state sponsors would likely maintain.See: http://en.wikipedia.org/wiki/Aral_smallpox_incident If we consider state weapon programs may modify orthopox viruses it is not out of the question that they could manipulate various orthopox virus including monkeypox. While it is difficult to increase virulence, indeed it is not beyond the capabilities of a state weapon lab to do so. Epidemologcial surveillance of monkeypox and other re-emerging orthopox  virus is critical to forecasting risk and adjusting vaccination strategies.


For more indepth analysis on Monkeypox see: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074816;jsessionid=ABD632A53AE2192A4B10BE9883D4443D

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