The poliovirus strain that caused an outbreak in the Republic of the Congo in 2010 is able to resist the immune responses generated by a commonly used vaccine. The finding could explain why the outbreak, which killed nearly half of the 445 people infected, was so severe.
Christian Drosten at the University of Bonn Medical Centre in Germany and his colleagues analysed the virus strain responsible for the outbreak. They found a combination of two mutations, both in the proteins of the strain's 'coat', which make it harder for certain antibodies to stick to the virus. People who died in this outbreak had been vaccinated in the past, but people who were freshly re-vaccinated could fight off the virus.