According to research published in the scientific journal Nature, the vaccine, designed to prevent harmful mutations, is considered key to eradicating the disease
October 29, 2020 Share on FacebookShare Share on TwitterTweet Share on WhatsAppShare
The possible resurgence of almost eradicated diseases in Latin America, such as polio, appears as one of the worst threats in the post-COVID-19 world (Europa Press)
A vaccine against a type of polio that is spreading in the southern hemisphere is expected to receive emergency approval before the end of the year, warns research published in the scientific journal Nature . If it does, it will be the first time the World Health Organization has directed an unlicensed vaccine or drug through its emergency listing process.
Wild polio has almost been eradicated. Only two countries, Afghanistan and Pakistan, still report cases . But a naturally-born version of the virus from the weakened polio virus used in vaccination is on the rise.
What is called circulating vaccine-derived poliovirus (cVDPV) is increasing in both Afghanistan and Pakistan, as well as in the Philippines, Malaysia, Yemen, and 19 African countries, with Chad, the Democratic Republic of the Congo, and the Ivory Coast the most. affected from Africa.
So far in 2020, there have been more than 460 cases of vaccine-derived polio worldwide. This is more than 4 times the number detected right now in 2019, which is a major problem for the 32-year, $ 17 billion global campaign to eradicate the disease. Researchers modeling polio infections say that for every known case, there are about 2,000 infections in the population.
“Millions of people potentially have no immunity to the vaccine-derived virus, and that is why we are very concerned,” says Kathleen O'Reilly, an epidemiologist at the London School of Hygiene and Tropical Medicine who models polio infections.
The WHO is in the last stages of considering whether to approve it more quickly, under what is called an emergency use list, a procedure that was created during the 2014-16 Ebola outbreak in West Africa, and that the agency also is being prepared for use for coronavirus vaccines (REUTERS)
Independent scientific advisers from the World Health Organization (WHO) have been evaluating a vaccine specifically designed to protect against cVDPV. This vaccine, which has been in the works for a decade, has been tested for safety and efficacy, but is not yet licensed and needs to undergo further trials. The WHO is in the last stages of considering whether to approve it more quickly, under what is called an emergency use list , a procedure that was created during the 2014-16 Ebola outbreak in West Africa, and that the agency also is being prepared for use for coronavirus vaccines.
After a press conference on October 9, Alejandro Cravioto, chairman of the WHO Strategic Advisory Group of Experts on Immunization, told Nature that it is the first vaccine to be considered on the emergency use list. “It will be a very good exercise for us to see how this works, because probably some of the COVID-19 vaccines will have to be authorized for use in the same way,” said the specialist.
Most cases of cVDPV are caused by mutations in a strain of poliovirus called type 2. Right now, outbreaks are being addressed with the older type 2 polio vaccine, which is at risk of further outbreaks. If the new vaccine is cleared for emergency use, that could be a “game changer,” says Simona Zipursky, who co-chairs the vaccine working group at the Global Polio Eradication Initiative in Geneva, Switzerland. The initiative is a partnership between WHO and international donors.
If national medical regulators agree, the new polio vaccine could be distributed in selected pilot countries within two months of WHO approval, Zipursky warns .
Polyemyelitis was one of the most feared diseases. It attacked the boys, produced deaths and paralysis, until in 1955, Jonas Salk obtained a vaccine that managed to fight it. Then Albert Sabin created the oral vaccine (Shutterstock)
Medical researcher Albert Sabin developed the conventional polio vaccine in the 1950s and 1960s, growing the virus in nonhuman primates and cell cultures, until it adapted to those environments and was no longer good at infecting humans. . This 'attenuated' virus is used as a vaccine, with the result that today only a few hundred are infected and a much smaller number paralyzed each year by a disease that used to infect hundreds of thousands.
The vaccine must be taken orally and the live virus is excreted in the feces by recipients for a later period. If this virus is ingested by other people, for example in contaminated drinking water, it can infect them. It is usually harmless because the virus is attenuated. And it might even boost immunity against polio, just as it does for those directly vaccinated.
But what Sabin never knew, says Raúl Andino, a virologist at the University of California, San Francisco, was that his attenuation of the virus was hanging by a thread. It only took a “guardian mutation” in the RNA of the virus to allow other changes to allow it to regain virulence. And this happened, possibly as early as 1988, when a vaccine-derived polio outbreak began in Egypt. In later years, more cases emerged, even though wild polio was on its way to being eliminated in most countries.
A turning point came in 2015, when eradication of wild type 2 polio was declared, 16 years after the last case was reported. The WHO decided to withdraw the oral type 2 vaccine worldwide in a large coordinated act in 2016. After this, immunity to type 2 polio began to wane, leaving communities vulnerable when some type 2 viruses lurking from the vaccines became dangerous again.
A decade of research
Like the old polio vaccine, the new vaccine is derived from the live, infectious virus, but this time it has been 'triply blocked' using genetic engineering to prevent it from becoming harmful. Andino began work on this redesign in 2011, with colleagues like Andrew Macadam at the UK's National Institute for Biological Standards and Control and others at the US Centers for Disease Control and Prevention.
Macadam targeted parts of the RNA in Sabin's vaccine where individual bases were mutated to restore virulence of the virus. He exchanged some of these bases for others at strategic points, chosen so it would be difficult for the virus to undo the alteration. “It works amazingly,” says Andino. “We no longer saw a mutation in this, not in cell culture, not in animal models and now, not in humans.”
The team made two more alterations to the virus: one to prevent it from recombining with other intestinal viruses; the other to slow down its evolution. The result is a viral vaccine with a much lower chance of causing polio.
In 2015, the Bill and Melinda Gates Foundation in Seattle, Washington, agreed to fund a $ 150 million program of concurrent clinical trials and manufacturing of the new vaccine ; the nonprofit global health organization PATH , also based in Seattle, is coordinating the project. While the program is underway, WHO is sharing its trial data with the African Vaccine Regulatory Forum, a network of national regulatory authorities.
“The vaccine is never imposed on a country and it has to go through its own process to approve it,” says Zipursky . But he adds that regulators are eager to get hold of the vaccine so they can finally rid their countries of polio and focus on other priorities.
Preparation for unexpected findings
There is still a small risk that this vaccine could also be reversed and start causing disease, says Paul Fine, a communicable disease specialist at the London School of Hygiene and Tropical Medicine (Shutterstock)
There is still a small risk that this vaccine could also be reversed and start causing disease, says Paul Fine, a communicable disease specialist at the London School of Hygiene and Tropical Medicine. “I think at the end of the day it will come down to: how stable is this,” he says.
A rare adverse event would be detected only in larger trials , warns Abdhalah Ziraba, an epidemiologist at the Center for African Health and Population Research in Nairobi. The specialist has his doubts about the emergency deployment; He says “it makes sense where you don't have any tools in your arsenal, like with Ebola or COVID-19. But polio and COVID-19 are light years apart in terms of what constitutes an emergency. “
Zipursky explains that authorization for emergency use requires intense monitoring in the first three months after the vaccine is implemented, so that nations can “respond to any unexpected findings.” It is essential, he says, “so that we are not undermining not only the polio program, but immunization in general.”
However, for Nicholas Grassly, an infectious disease epidemiologist at Imperial College London, implementation cannot wait. Grassly argues that the world is responding to cVDPV outbreaks using hundreds of millions of doses of the ancient type 2 polio vaccine, which in turn are spreading more outbreaks. The new vaccine, he adds, “is the only tool we have to stop this cycle.” The expert argues that the lack of data from more trials is offset by historical data from the previous vaccine, which is similar in many respects and shows minimal adverse effects.
Faisal Shuaib, Executive Director of the National Agency for the Development of Primary Health Care in Abuja, which is responsible for eradicating polio in Nigeria, welcomes the new vaccine “as long as it meets the safety profiles established by regulatory organizations. world and national ”. But “it is not a silver bullet,” he adds. “It's very important, but ultimately the solution is to make sure we put in all the necessary resources to improve routine immunization.”
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