Safer polio vaccine strains for post-eradication era developed

Live attenuated (weakened) vaccine strains carry genetic mutations that prevent them from causing disease, but they can - in rare cases - revert to more dangerous (or virulent) virus.

After eradication, the World Health Organisation plans to stop the use of live-attenuated polio vaccines, the study said.

In addition, to improve safety, WHO has strongly encouraged new manufacturers to switch the source of inactivated virus from virulent wild-type strains to an attenuated strain, named after the polio vaccine pioneer Sabin.

The researchers started with a Sabin vaccine strain and modified a particular region of the viral RNA in ways that they predicted would make the resulting strains genetically stable (i.e. they would not revert to wild-type or other virulent forms).

They then compared these new strains with both the original Sabin vaccine strain and the wild-type strain currently used in the production of inactivated vaccine.

Besides testing the genetic stability of the new strains, the researchers examined their ability to grow in tissue culture (necessary for vaccine production), their risk for causing paralysis in mice engineered to carry a human polio-virus receptor, and whether--after inactivation--they effectively immunized rats.

In all these tests, the new strains behaved as predicted, that is, they are effective, suitable to mass production, and safer than the alternatives.