2023-06-14 17:20:36
The eradication of poliomyelitis is one of the goals of the World Health Organization (WHO). Despite the fact that cases caused by wild poliovirus have decreased by more than 99%, from the 350,000 estimated in 1988 to the six reported in 2021, as long as there are cases, it cannot be considered eradicated.
But now two new vaccines that induce immune responses in mice may increase the chance of eradicating this disease. The candidates, based on a weakened version of the poliovirus, are less likely to generate virulent vaccine-derived poliovirus variants than some of the earlier vaccines.
Polio is caused by three different versions (or serotypes) of the poliovirus. Wild poliovirus (WPV) types 2 and 3 have been eradicated in the past decade, thanks to the development of vaccines that use an inactivated version of the virus or attenuated polioviruses (versions weakened enough not to cause disease but elicit a response). immune).
Oral vaccines use live, weakened viruses that occasionally mutate into an active form, causing outbreaks even in countries thought to have eliminated polio. For example, WPV type 1 still causes disease in Afghanistan and Pakistan, and two other types of poliovirus that arise from evolution of the virus in the vaccine to a virulent form continue to circulate.
Scientists from the University of California-San Francisco (USA) and the UK’s National Institute for Biological Standards and Control (NIBSC) have developed two new oral polio vaccines (nOPV). They are the first vaccines against polio in 50 years.
“With such variability in vaccination within and between countries, the polio virus has persisted into the 21st century, with sometimes tragic consequences,” said Raul Andino, co-lead author of the paper with Andrew Macadam. “We have designed these new vaccines using the lessons learned from many years of fighting polio and we believe they will help eliminate the disease once and for all.”
The recently developed oral polio vaccine type 2 (nOPV2), which uses a live attenuated virus, is effective in inducing an immune response, while remaining genetically stable, and has been used against vaccine-derived poliovirus variants. This stability is due to the inclusion of genetic components that prevent the virus from regaining virulence.
Despite its efficacy, nOPV2 only protects against one of the three strains of polio, and cases of polio have emerged recently in Israel, as well as in parts of the US where people refuse to vaccinate their children.
Even where there are no cases of polio in hospitals, polio continues to be detected in the wastewater of major cities. There may be 99% fewer cases of polio today than 30 years ago, but the last 1% have proven difficult to eliminate. «If there is polio somewhere, it will return where there are gaps in vaccination», warns Andino.
The two new vaccines are currently being tested in clinical trials to ensure they are effective and do not revert to dangerous forms in humans. Andino is hopeful that they will be incorporated in bivalent or trivalent combinations with nOPV2.
Children of the future will be similarly protected from polio for life, and perhaps the world will one day experience decades of zero polio detection.
«The perception that polio is gone is dangerous. For example, in India alone, 500,000 children are born every week, a huge number of susceptible people. Now we have what we need to protect them,” recalls Andino.
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