Vaccine-derived poliovirus in Nigeria
(Nigeria - 5 October 2007) — As recently reported by various news organizations, 69 cases of polio due to a vaccine-derived poliovirus have been confirmed in nine northern states of Nigeria. These cases are vaccine-derived, which means they came from a changed form of a strain found in the oral polio vaccine (OPV).
OPV contains a live but weakened form of poliovirus. On very rare occasions, polio strains derived from OPV mutate and regain the ability to paralyze and may spread in communities where immunization rates are low, especially in densely populated areas where there is poor hygiene and poor sanitation.
In the affected areas of Nigeria, polio immunization rates were not high enough to protect all children. The vaccine-derived poliovirus in Nigeria was first noted in August 2006, and response plans were implemented.
The most effective way to counter such outbreaks is to intensify efforts to raise the immunization rates, which means reaching more children with the oral polio vaccine. Thus, four mass immunization campaigns have been carried out since the outbreak was identified.
Vaccine-derived polioviruses are extremely rare. Of the more than 10 billion doses of OPV received by more than two billion children in the past 10 years, fewer than 200 vaccine-derived cases have been reported, while 6.5 million cases of childhood paralysis were prevented. During this same period, the wild poliovirus, our real enemy, paralyzed more than 33,000 children.
Tremendous progress has been made toward ending polio worldwide through the use of OPV. In the 1980s, 350,000 children were infected by this crippling disease each year. In the two decades since, polio cases have been slashed by 99 percent. Less than two thousand cases were reported in 2006.
OPV has been the experts’ vaccine of choice in over 195 countries that have successfully eradicated polio. It remains the Global Polio Eradication Initiative’s (GPEI) recommended vaccine to finish polio eradication.