An update on the African polio outbreak

Poliovirus invades the nervous system, resulting in paralysis and occasionally death. In 1988, a global initiative was launched by the WHO and partners to eradicate the virus by mass immunization. The effort was largely successful; the number of polio cases fell by 99%, and today the virus remains endemic to just four countries: India, Pakistan, Afghanistan, and Nigeria (1). However, in November and December of last year, hundreds of polio victims were identified in the Congo, and an estimated 40% of those cases were fatal. The JCI recently spoke to Vincent Racaniello, selfdescribed “virus guy” and polio expert at Columbia University, about the outbreak. JCI: Is the poliovirus currently circulating in Africa different from that seen in the rest of the world? Racaniello: There is no evidence that the poliovirus circulating in Africa (specifically in the Congo) has changed in any way. The Congo strain appears to have come from India via Angola, possibly spread by migrant workers. It is a wild-type 1 strain, not a vaccine-derived strain that has caused outbreaks in other countries. JCI: Most of the victims in the Congo are teenagers and young adults, and the fatality rate is high; does that signal that the virus has changed in some way? Racaniello: The high prevalence of infection among teenagers and young adults is likely related to gaps in immunization. The last case of polio in the Congo was in 2000; hence immunization has lagged. When polio is acquired at a later age, the disease tends to be more severe. JCI: How far do you think this latest outbreak is likely to spread? Racaniello: Mass immunizations will probably restrict the outbreak to the Congo. However, consider that only 1% of poliovirus infections are paralytic. That means in the current outbreak, where 476 cases of paralytic disease have been recorded, there have been a total of 47,600 infections, 99% of which have gone unnoticed. Therefore the potential for spreading the infection to neighboring countries is high — unless those countries maintain high levels of immunization. Migrant worker travel can also cause distant spread of infection. In 2004, there was an outbreak of polio in Nigeria; the virus spread to other countries in Africa and then to Indonesia. JCI: How should vaccination policy change to prevent future outbreaks? Racaniello: All countries need to maintain high levels of immunization coverage until the disease has been eradicated. In the US and other developed countries, this is done by routine immunization at birth. In underdeveloped countries, this is difficult due to poor health care systems, unstable political situations, and armed conflict. Hence, mass immunizations are used to improve coverage. As long as countries such as the Congo allow immunizations to lag, there will be outbreaks.