Academic journal article Bulletin of the World Health Organization

Poliovirus Vaccine Strains Will Continue to Circulate Long after Wild Strains Have Been Eradicated

Academic journal article Bulletin of the World Health Organization

Poliovirus Vaccine Strains Will Continue to Circulate Long after Wild Strains Have Been Eradicated

Article excerpt

Before discussing the eradication of the poliovirus, we must first evaluate the differences between the poliovirus and smallpox strains, and between the eradication programmes of each virus. Smallpox virus strains in all but two of the diagnosis laboratories have been destroyed; however, live poliovirus vaccine strains will continue to circulate in many countries as oral vaccine strains or recombinants of them, long after wild strains have been eradicated.

Smallpox is a single virus that has two varieties, variola major (vera) and variola minor (alastrim), which differ in virulence. The genomes of these strains are very stable, and no recombinations with other poxviruses were known to occur during the smallpox eradication programme. Poliomyelitis is caused by an RNA virus with three serotypes and vaccine and wild strains, which have been circulating in many countries for decades. The virus can undergo recombination after replication in the human gut, and this has a tendency to increase the virulence of the vaccine strains.

Because most developing countries will probably continue to use the oral poliovirus vaccine (OPV) as the price of the inactivated product is so high, poliovirus will continue to circulate and infect vaccinees and contacts with vaccine-derived or partially modified polio strains. This situation is very different from what happened after smallpox eradication, when the vaccine was no longer used. …

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