Polio Vaccine - Iatrogenic (vaccine-induced) Polio

Iatrogenic (vaccine-induced) Polio

A major concern about the oral polio vaccine (OPV) is its known ability to revert to a form that can achieve neurological infection and cause paralysis. Clinical disease, including paralysis, caused by vaccine-derived poliovirus (VDPV) is indistinguishable from that caused by wild polioviruses. This is believed to be a rare event, but outbreaks of vaccine-associated paralytic poliomyelitis (VAPP) have been reported, and tend to occur in areas of low coverage by OPV, presumably because the OPV is itself protective against the related outbreak strain.

As the incidence of wild polio diminishes, nations transition from use of the oral vaccine back to the injected vaccine because the direct risk of iatrogenic polio (VAPP) due to OPV outweighs the indirect benefit of immunization via subclinical transmission of OPV. When IPV is used, reversion is not possible but there remains a small risk of clinical infection upon exposure to reverted OPV or wild polio virus. Following the widespread use of polio vaccines in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. The use of OPV was discontinued in the United States in 2000 and in 2004 in the UK, but it continues to be used around the globe.

The rate of vaccine-associated paralytic poliomyelitis (VAPP) varies by region but is generally about 1 case per 750,000 vaccine recipients. VAPP is more likely to occur in adults than in children. In immunodeficient children, the risk of VAPP is almost 7,000 times higher, particularly for persons with B-lymphocyte disorders (e.g., agammaglobulinemia and hypogammaglobulinemia), which reduce the synthesis of protective antibodies. The World Health Organization considers the benefits of vaccination to far outweigh the risk of vaccine derived polio. Outbreaks of vaccine derived polio have been stopped by multiple rounds of high-quality vaccination, in order to immunize the entire population.

Outbreaks of VAPP occurred independently in Belarus (1965–66), Canada (1966–68), Egypt (1983–1993), Hispaniola (2000–2001), Philippines (2001), Madagascar (2001–2002), and in Haiti (2002), where political strife and poverty have interfered with vaccination efforts. In 2006 an outbreak of vaccine-derived poliovirus occurred in China. Cases have been reported from Cambodia (2005–2006), Myanmar (2006–2007), Iran (1995, 2005–2007), Syria, Kuwait and Egypt. Since 2005, The World Health Organization has been tracking vaccine-caused polio in northern Nigeria caused by a mutation in live oral polio vaccines.