by Matthew Bowdish, MD
The World Health Organization (WHO) reports that approximately 180 Nigerian children have become paralyzed by polio as a result of widespread vaccination efforts in Africa’s most populous country. The outbreak is from the use of an oral polio vaccine (OPV) that contains a live-attenuated form of the poliovirus.
OPV was initially developed by Albert Sabin in the 1950s. A live-attenuated poliovirus vaccine is ingested and stimulates the lymphatic tissue in the gut to resist future infections since the gastrointestinal tract is the major transmission route for natural poliovirus.
The oral vaccine is also preferred in developing nations due to its cheap production costs, easier administration (i.e. no needles/syringes required) and better efficacy than the injected killed virus vaccine used in the developed world.
However, the use of live-attenuated poliovirus vaccine has its downsides. Live virus is processed in the gut and then passed out via defecation into the environment. If the virus mutates and if public sanitation is unavailable, then infective virus can be spread to other non-vaccinated children. This seems to be the case in Nigeria.
Vaccine-derived poliovirus (VDPV) infection can occur in countries using OPVs and public health officials need to weigh the risks of this iatrogenic infection with the overall disease burden. So while 42 million people have been vaccinated against polio in Nigeria, around 180 children have been paralyzed over the last two years.
This episode may also have implications for Nigeria’s large Muslim minority, which has been reluctant to take part in vaccination efforts due to concerns about adverse effects, the unfounded fear of vaccines contaminated with HIV and due to Muslim distrust of the international organizations involved in promoting the vaccine program.
I also wonder whether anti-vaccination advocates in the developed world will use the Nigerian program as fodder for their own opposition to other vaccines such as MMR, which they claim to be the cause autism and other disorders.
Matthew Bowdish is an allergy and clinical immunology specialist.
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