A new polio vaccine that could tackle mutated strains of the disease has passed phase II clinical trials, according to two studies published in medical journal The Lancet.
The vaccine, called nOPV2 and administered orally, is the first that works against poliovirus type 2, a mutated form of the virus that has been responsible for outbreaks in Africa and Asia.
The development follows a surge in cases of type 2 poliovirus and amid warnings that millions of children are missing out on vital vaccinations as a result of the COVID-19 pandemic.
Poliovirus type 2 — also known as circulating vaccine-derived poliovirus — developed from an existing oral vaccine and is causing around 90 per cent of new polio cases around the world.
For this reason, the type 2 component of the existing polio vaccine was withdrawn from use in May 2016. Despite this, globally recorded type 2 poliovirus transmissions increased from 71 in 2018 to 784 so far in 2020, most of these in Pakistan, Afghanistan and parts of Sub-Saharan Africa.
The nOPV2 vaccine has been tested in 1,200 adults, children and infants and has received an Emergency Use Listing from the World Health Organization (WHO), meaning it can be deployed in global health emergencies. It will now be used in the field to combat polio outbreaks in central Africa until enough studies have been done to approve it for wider use.
According to Ricardo Rüttimann, the vaccines unit director for Fighting Infectious Diseases in Emerging Countries, a group based at the University of Miami in the United States, the next stage of approval could happen as soon as mid-2021.
Rüttimann told SciDev.Net that the vaccine's arrival was timely, as there was great concern in the medical community about existing polio outbreaks, and the effect of the COVID-19 pandemic on vaccination programs. According to the WHO, at least 80 million infants around the world have missed out on important immunization this year, including against polio.
All vaccine programs worldwide were heavily impacted during the pandemic. Safer vaccines generate better compliance and improve coverage, which translates into more effectiveness."
Ricardo Rüttimann, vaccines unit director for Fighting Infectious Diseases in Emerging Countries
The nOPV2 vaccine was tested among children in Panama, where it was proven to have lower stool shedding than existing polio vaccines — a rare problem where a newly immunized person passes some of the virus in their stool. This can put carers of infants at risk of infection if the carers are not immunized against the disease.
Ilse de Coster, vaccine researcher at the University of Antwerp and a researcher for the polio study, said: "To stop type 2 polio outbreaks, high-quality immunization campaigns with oral polio are used to reach every child, but this always carries the small risk to seed new cVDPV (circulating vaccine-derived polio virus) circulation.
"NOPV2 is a modified version of the existing type 2 vaccine that clinical trials have shown provides comparable protection against type 2 poliovirus, while being more genetically stable and less likely to revert to a form that can cause paralysis."
The new vaccine candidate may also help alleviate another problem — that of vaccine hesitancy. The fact that a component of the existing vaccine had to be withdrawn due to the risks of creating mutated polio strains has reportedly made parents around the world more reluctant to get their children immunized.
Claudia Martinez, research program manager for the Access to Medicine Foundation, said: "New strains from vaccines can cause concern for parents. The necessity to ensure vaccines are safe and effective has to be paramount concern."
Martinez said the new vaccine was "very encouraging", but cautioned that global health organizations and governments must remove remaining barriers to ensure it can take full effect. According to the foundation, these include shaping markets so that enough vaccine doses are produced and sold at affordable prices, and improving transport and storage facilities.
"A vaccine is only as good as the number of people it can reach," added Martinez.
De Coster also stressed the importance of high uptake, adding: "The most important tool to eradicate polio globally is immunization at high coverage. Only sufficiently high coverage can stop the circulation by preventing the weakened virus passing between individuals."