Researchers have genetically altered oral polio vaccines to significantly reduce the likelihood of the weakened virus mutating into a dangerous form that can cause outbreaks and paralysis.
Polio is a highly infectious viral disease that largely affects children aged under five years. The virus is transmitted by person-to-person and multiplies in the intestine, from where it can invade the nervous system and cause paralysis.
Cases have decreased by over 99% since 1988, from an estimated 350,000 cases in more than 125 endemic countries to six reported cases in 2021, and more than 20 million people who would otherwise have been paralysed are able to walk today thanks to vaccines.
Endemic ‘wild’ poliovirus remains in border areas of Pakistan and Afghanistan, according to the World Health Organization, and oral vaccines play a crucial role in the attempt to eradicate polio.
However, if allowed to circulate in places where vaccine coverage is low, or replicate in an immunodeficient individual, the weakened live poliovirus contained in oral polio vaccine can mutate to a form that causes illness and paralysis.
There are now more cases of vaccine-derived polio than of the wild poliovirus, and the polio detected in London’s sewers last year was connected to the oral vaccine.
The development of the two new vaccine candidates has been detailed by the team from the University of California, San Francisco and the UK’s National Institute of Biological Standards and Control (NIBSC) in Nature.
The two vaccines were tested in mice and found to be effective, safe and stable, and are now being tested in clinical trials to ensure that they are both effective and do not revert to dangerous forms in humans.
“Our experiments in mice and deep sequencing analysis confirmed that the candidates remain attenuated and preserve all the documented nOPV2 (new type 2 OPV) characteristics concerning genetic stability following accelerated virus evolution,” the research outlines. “Importantly, these vaccine candidates are highly immunogenic in mice as monovalent and multivalent formulations and may contribute to poliovirus eradication.”
Andino, co-senior author of the paper, said: “With such variation in vaccination within and between countries, poliovirus has persisted into the 21st century, with sometimes tragic consequences.
“We’ve designed these new vaccines using lessons learned from many years of fighting polio and believe they will help eliminate the disease once and for all.”