Researchers are preparing for a post-polio world. Once polio
is eradicated, the World Health Organization plans to replace live-attenuated vaccines with ones made from inactivated attenuated virus. This led researchers at the National Institute for Biological Standards and Control in the UK to design new safe and effective vaccine strains.
Currently, two types of polio vaccines are in use - a live-attenuated
vaccine and an inactivated
one. The live-attenuated vaccine is made from a virus with mutations that make it less virulent. However, this attenuated virus can survive in the guts of immunocompromised individuals, where it can accumulate mutations that make it more virulent.
The inactivated vaccine is made from virulent virus killed with formalin. While these vaccines can’t spread live virus, the virus must still be grown in large quantities to produce the vaccine. This means there is a risk that live, virulent polio virus could “escape” from a lab and spread through the population. To curb this risk, Philip Minor and colleagues set out to design attenuated polio strains to be used for inactivated vaccines.
These attenuated strains are based on the well-studied Sabin vaccine strain
, but the capsid
genes are modified, making them less likely to mutate into a virulent virus. They grow well in tissue culture, do not cause significant disease in mice, and unlike the Sabin strain, they do not infect non-human primates. According to minor, “we have developed new strains for (vaccine) production with negligible risk to the human population should they escape”, which will “allow for safe vaccine production in the post-eradication world”.
, PLOS Pathogens