London, Jan 1 (IANS): Researchers have developed new polio vaccine strains that is particularly suitable for a post-eradication era as these strains appear both effective and unable to cause disease after accidental release.

While the goal of polio virus eradication is in sight, there are concerns about post-eradication manufacturing and stockpiling vaccine stores containing live virus that could escape and repopulate the environment.

"We have developed new strains for IPV (inactivated polio vaccine) production with negligible risk to the human population should they escape", said the researchers.

The attributes of the new strains "allow for safe vaccine production in the post-eradication world," the study noted.

Different types of polio vaccines currently exist, but none are optimal from a safety point of view, the researchers from National Institute for Biological Standards and Control in Hertfordshire, Britain, noted.

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.

The study was published in the journal PLOS Pathogens.