Newly developed polio vaccine strains could replace currently used risky inactivated vaccines, thereby allowing for safer vaccine production in a post-polio eradication environment, according to researchers at the National Institute for Biological Standards and Control (NIBSC).

Polio eradication is in sight, and these new strains are safer than the attenuated Sabin strain currently used for developing inactivated vaccine. The Sabin strain is unstable and thus could repopulate the environment, Sarah Knowlson and her colleagues from the NIBSC, Potters Bar, Hertfordshire, England, argue in an article published Dec. 31 in PLOS Pathogens.

“The Global Polio Eradication Initiative is … very close to eliminating naturally occurring wild poliovirus from the planet. It has involved the extensive use of both the live attenuated vaccines that can revert to a wild type phenotype, and inactivated polio vaccines (IPV) whose production in the main currently requires the growth of very large amounts of virulent wild type poliovirus, ” they explain, noting that the vaccines are therefore a possible source for re-emergence of poliomyelitis following eradication. ( PLoS Pathog. 2015 Dec 31;11. doi: 10.1371/journal.ppat.1005316 ).

To develop the new strains, the researchers started with the well-understood Sabin strain and modified a region of its viral RNA to promote greater genetic stability. The new strains were then compared with the original Sabin vaccine strain and the wild-type strain currently used to produce inactivated vaccine.

The new strains were “extremely attenuated and genetically stable in cell culture by rational design based on understanding of the attenuation of the Sabin vaccine strains of poliovirus. The viruses grow to titers acceptable for IPV production under appropriate conditions of temperature and cell substrate and have the same antigenic properties based on reactions with panels of monoclonal antibodies in ELISA as well as in regulatory assays for antigen and immunogen content as the strains from which their capsids were derived,” the investigators wrote.

The strains were tested in mice and primates and behaved as predicted in that they were “effective, suitable to mass production, and safer than the alternatives,” according to a press statement.

This work was supported by NIBSC. The investigators reported having no disclosures.