A new polio vaccine can fight its resurgence

BILLIONThe recent recurrence of polio has come like something of an epidemiological thunderbolt. That was in 1979 Polio has been officially declared eradicated in the US — a first step in a multi-generational effort to eradicate the disease around the world. However, on July 21, the New York State Department of Health reported a case of polio in an unvaccinated man in Rockland County, and since then, circulating poliovirus has been found in wastewater there and in neighboring Orange County, as well as in New York City. In London, the virus was also found in sewage in February, and in Jerusalem, a case appeared that same month.

The three cases, although seemingly separate, point to a worrying trend – one that goes against more than three decades of progress in eliminating the disease. In 1988, polio was endemic in 125 countries and resulted in the death or paralysis of 350,000 people – mostly children – each year, according to the World Health Organization (WHO). But thanks to a massive vaccination push by WHO, Rotary International, UNICEF, the US Centers for Disease Control and Prevention (CDC), and more, polio has now become endemic in just two countries – Afghanistan and Pakistan – witnessed there are only 18 cases between them up to the present this year.

However, polio is on the rise again, and health officials are now wary of what Paul Andino-Pavlovsky, professor of microbiology and immunology at the University of California, San Francisco, calls “” “silent disease” worldwide. “This is just the tip of the iceberg,” he warned.

Yvonne Moldanado, a professor of global health and infectious disease at Stanford University School of Medicine, added: “The case we have seen [in New York] is unusual but is a red flag that we need to watch out for potential outbreaks. We run the risk of developing more cases of polio.”

The bad news is that polio is stalking us again. The good news is that just in the past year, a new vaccine has been added to the existing polio vaccine stockpile — one that, properly deployed, can stop an outbreak of polio. new global paralysis before it can begin. No problem, the resurgence of the disease has posed a series of challenges — all of which need to be met if polio is to be contained.

What’s behind the current outbreak?

Many factors have played a role in the return of polio – not least of which is complacency, especially in the United States and other developed countries. When the majority of people alive have never experienced a case of a certain disease, it is easy to dismiss it. “People don’t remember polio, they don’t see it,” said Ian Lipkin, professor of epidemiology at Columbia University’s Mailman School of Public Health. “There’s something about our species that makes us forget the importance of these things.”

That can lead to delays in vaccine compliance — something that shows in the U.S. Nationally, 92.6% of children are fully immunized against polio before the age of 2. , According to CDC. Broadly speaking, that’s an encouraging number, but vaccination rates vary from state to state and even from county to county. In Oklahoma, for example, the polio vaccination rate is just 79.5%, and in South Carolina it’s 80.3%. In the zip code of Rockland County, where the polio case occurred in June, vaccination rate at an alarmingly low 37.3%.

The COVID-19 pandemic also has play a role in the return of the disease. Dr William Schaffner, professor of infectious diseases at Vanderbilt College of Medicine in Nashville, Tenn, said: “In the age of COVID, families are not seeing their doctor or pediatrician as often as they normally would. lag behind their usual vaccination schedule”.

According to Moldanado, the rate of polio vaccination among children has decreased by only 1% since the beginning of the pandemic. But when it comes to infectious diseases, even a single percent can matter a lot. “It means tens of thousands of children are not fully immunized, and those children are at risk of diseases that really shouldn’t exist in well-resourced countries,” Moldanado said.

Read more: Polio is back. Here’s how to keep yourself safe

Vaccine paradox

The irony in the return of polio is the vaccination campaign itself CDC estimates which has averted 16 million cases of paralysis and 1.5 million deaths since 1988 is also partly responsible for the new resurgence. There are two types of polio vaccine. The first, called inactivated polio vaccine (IPV) – given by injection – uses a killed virus to familiarize the body with the disease and help it recognize and attack a live virus if it encounters it. The other, called the oral polio vaccine (OPV)—which is given by mouth—uses an attenuated or weakened virus that can do the same job as primer for immune system, without actually causing the disease. The advantage of OPV is that it is easier to manage and cheaper, which is why it is used in global eradication campaigns. The major disadvantage is that in rare cases, a weakened vaccine can revert to its virulent strain. That can lead to disease in vaccinated people, and even if they don’t, the resurgent virus will be shed in the feces, enter wastewater, and potentially infect others. For that reason, the US switched to IPV exclusively in 2000 – although cases of the virus reversing are extremely rare.

“The rough estimate is that one in 3 million doses of oral vaccine will result in a case of polio in the U.S. before 2000,” says Schaffner. “It’s rare, but it’s not small.”

Indeed it is not. Gene sequencing revealed that the virus that caused the recent cases in New York and Jerusalem and was found in London wastewater is known as circulating vaccine-derived poliovirus (cVDPV). So far this year, cVDPV has resulted in another 535 cases of polio in 18 other countries, based on Global Polio Eradication Initiative (GPEI).

But IPV also has problems – beyond the difficulty of comparison management. OPV, as it is taken orally, establishes what is known as intestinal immunity. Assuming the vaccinated person is not one of the unlucky few to have the virus revert to a virulent form, the virus will not replicate in the intestinal system and therefore no virus will be released. excreted in feces. IPV protects recipients from contracting polio, but does not prevent intestinal replication and spread if the person has been infected with cVDPV.

Andino-Pavlovsky believes that sampling wastewater anywhere in the world where IPV is used could give rise to certain circulating vaccine-derived polioviruses that IPV recipients have contracted. disease, reproduce and eliminate, endangering unvaccinated people. “In Europe, in the US, in Australia — everywhere people are getting inactivated vaccines — there is a possibility,” he said.

A new vaccine

Even with the limitations of both vaccines, vaccination is clearly better than no vaccination, as all vaccine recipients are protected against contracting polio. symptomatic paralysis. But OPV and IPV do exist in a state of stress, with one vaccine virus and another contributing to its spread. For that reason, WHO and other global health organizations call for a eventual move to IPV – a move that will mean no vaccine-derived viruses will be detected and eliminated.

“We need to stop supplying the live virus so it stops circulating,” says Moldanado.

However, that’s not realistic at the moment — not while there are still millions of babies and children in need of vaccines in developing countries, where IPV is still too expensive and people getting vaccinated If a skilled operator can perform the injection, the supply is much lower than that of field staff. who require little special training to administer drops by mouth. As a backstop, WHO, the Bill and Melinda Gates Foundation and the UK’s National Institute for Biological Control and Standards have come together to develop a new oral vaccine that is much more stable than previous versions. , reducing the likelihood of infection with attenuated virus is used. in the drops each returned to its unique state.

Andino-Pavlovsky, who was on the team that designed the vaccine, explains that it works by targeting the site on the virus’s genome that is responsible for the virulence reversal. In existing OPVs, that part of the gene only needs to undergo a single mutation to switch from a harmless to a dangerous state.

“Essentially, what we did was modify this sequence,” he said, “so that a single point mutation cannot cause a reversal; a virus must now undergo four or five different changes before acquiring a more virulent phenotype. It’s basically a numbers game”. As Andino-Pavlovsky earlier described it with magazine Nature“It’s like putting a virus in an evolutionary cage.”

Andino-Pavlovsky said that the vaccine containing the nested virus was put into use by the end of 2021 and to date, more than 180 million doses have been given in 13 countries. “The new vaccine is just as effective as the previous one in generating immunity,” he said.[and is] can prevent silent epidemics. “

Ultimately, the goal is to push polio over the cliff to extinction — like smallpox did in 1980 — with a phased phase of slow elimination of all OPVs, widespread use of IPV, and eradication of all forms of the polio virus. polio circulates anywhere in the world. The current return of the illness is a reminder that that work is not nearly done. Until it happens, an old calamity will haunt us again.

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