Although the global initiative to eradicate poliomyelitis through routine vaccination has cut the number of cases by more than 99% in 30 years, there are still major epidemics occurring today such as in Congo in 2010, Tajikistan in 2010, and China in 2011. Researchers first blamed the epidemics on low vaccine coverage but recent research has actually shown that the cause of the epidemics is from a vaccine-resistant strain of polio.
The sequencing of the genetic material of the virus responsible for the epidemics shows two mutations of the proteins that form the capsid of the virus. This mutated virus evades the immune system since the immune system is unable to recognize the strain. A study of the resistance of this polio virus variant in vaccinated volunteers of Gabon shows that the antibodies made from the vaccine are less effective against the strain found in the Congo epidemic in comparison to the normal strains of poliovirus. Researchers estimate that 15-30% of the 60 people of this study would not have been protected if the Congo epidemic had reached them.
Although this strain is quite rare, it could re-circulate and cause another epidemic to the scales of the ones that occurred in recent years in Congo, Tajikistan, and China. This causes a problem for the global campaign to eradicate poliomyelitis especially in areas with insufficient vaccination numbers.