Why polio is making a comeback

Why polio is making a comeback

A little over a month ago, a young man in the New York metropolitan area was partially paralyzed after contracting polio. The news caused a stir, both because it is the third highly infectious virus to surprise the United States in three years, after monkeypox and coronavirus, but also because for decades the disease has stopped spreading in the United States. rich countries, where improved sanitation, vaccinations and solid public health funding had succeeded in keeping populations safe. The last natural case was recorded in 1979 in the United States, in 1994 in the American continent and in 2003 in the United Kingdom. Nonetheless, the virus has been found in the sewage of the county where the young man lives and in another neighboring county, as well as in the cities of New York and London. Of course, polio also exists in other parts of the world. Although a global campaign to eradicate the disease has been underway since 1988, last year the poliovirus caused forms of paralysis that cannot be treated or cured in two countries where it had never been contained and in 21 others where has reappeared.

The reappearance of the disease Experts, however, were not surprised at the reappearance of the disease in Western countries. For years, the fight against polio has been undermined by funding cuts, vaccine skepticism, short memories and the treacherous nature of the virus. "It should be a wake-up call - says Heidi Larson, professor and founder of the Vaccine Confidence Project at the London School of Hygiene and Tropical Medicine -. Until we can completely eradicate the virus, we are all at risk".

For public health experts this is a real emergency, since cases of polio paralysis represent the tip of the immunological iceberg: for every paralyzed person, at least hundreds more have probably contracted infections asymptomatic, offering the virus a refuge to replicate and spread. Wastewater test results have shown that polio has probably been circulating since February in London and for at least several months in New York.

The sense of urgency has prompted London health authorities to make booster doses available of the vaccine against the disease to all children aged 9 and under, while their counterparts in New York - where in some areas 40 percent of children are not vaccinated - have urged parents to bring children vaccinated.

The history of vaccines To understand how polio ended up in these cities, it is useful to retrace a bit of history. Two stories, actually: the one about the polio vaccine and the one about how it was used to eradicate the disease from the world.

Let's start from the vaccine formula, or rather from the formulas, since there are two, born of a fierce rivalry in the mid-twentieth century between scientists Jonas Salk and Albert Sabin. Salk's formula, the first to be approved, is injected; it uses an inactive version of the virus and prevents the development of the disease without blocking viral transmission. Sabin's formula, which arrived a few years later, instead uses an artificially weakened live virus. It blocks transmission and, being a liquid that is sprayed orally, it is cheaper to produce and easier to distribute, as it does not require trained healthcare workers or careful disposal of needles. These characteristics made the oral version of Sabin, known as Opv, the bulwark for polio control and the main weapon at the disposal of the global eradication campaign.

The oral vaccine had a unique advantage. Wild-type polio is actually an intestinal virus: it attaches to receptors in the lining of the gut, where it replicates before migrating to the nerve cells that control the muscles. But because it is found in the intestines, the virus is excreted from the body with feces and spreads to other people through contaminated water. Sabin's vaccine exploits this process: the vaccine virus replicates within a person's body, is excreted with feces, and spreads its protection to unvaccinated neighbors.

The vaccine's benefit hid however a serious flaw. Once in a million doses, the weakened virus re-developed wild virus neurovirulence, destroying motor neurons and causing poliomyelitis paralysis. The mutation made even a child harboring the inactive virus a potential source of infection, rather than protection. This risk prompted rich countries to abandon the oral version: in 1996, when wild polio was no longer present in the United States, the oral vaccine caused about 10 cases of polio paralysis in children. In 2000, the United States switched to the injectable formula, known as IPV, with the United Kingdom doing the same in 2004.

The slowdown in the global vaccination campaign Polio vaccination requires different doses to guarantee complete protection, which once obtained shields children from both the wild and vaccine-derived versions. The international vaccination campaign therefore continued to rely on OPV, arguing that the risk would decrease as more children received protection. It was a reasonable bet at a time when the campaign was still in its infancy and health authorities thought it would take 10-12 years to eradicate the disease. But due to funding shortages, political and religious unrest and the Covid-19 pandemic - which has imposed a slowdown not only on eradication activities but on all types of childhood vaccination - 34 years later, work is not still finished. Meanwhile, a total of 688 cases of paralysis due to so-called 'circulating vaccine-derived poliovirus' (cVdpv) occurred in 20 countries last year and only six cases of wild-type polio in three countries.

There is an additional complexity linked to the emergence of the vaccine-derived virus. Poliovirus occurs in three strains: types 1, 2 and 3. Originally, both vaccines contained all three types. As time went by and immunity increased, the strains began to manifest less frequently, albeit at different rates. The first to disappear was type 2, and in 2016 the authorities therefore decided to eliminate the strain from the OPV. In massive coordinated action, the disease eradication campaign replaced the three-strain vaccine with a bivalent one.

But eliminating the strain from the formula meant that if any type 2 virus re-emerged in the world - from the environment or from a person harboring a mutated version linked to the vaccine - defenses would be poor. And the decision to change the formula didn't pay off.

“I think the best way to describe it is as a mistake made in good faith - explains Svea Closser, medical anthropologist and associate professor at the Johns Hopkins Bloomberg School of Public Health studying polio eradication -. They did not expect the extent, spread and global reach of these type 2 outbreaks ".

Most of the vaccine-derived virus now in circulation is mutated type 2. It has mainly appeared in central Africa , where outbreaks have spread beyond national borders. Polioviruses found in New York and London are also of the same type. It is important to note that although these two viruses are related to each other and to vaccine-derived viruses found earlier in Israel, there is as yet no genomic evidence that they are related to African viruses. They have less genetic variation from the vaccine virus than those circulating in Africa, indicating that they have emerged more recently. It is likely that they were imported from a place that it once used Opv (like Israel in the 2000s) or continues to do so.

That's significant, and not just because these type 2 viruses may have emerged due to optimism misplaced linked to the transition to the IPV. The data on the incidence of poliomyelitis - about one case of paralysis for every 200 infections - comes from research on type 1. Some data, however, show different numbers for the type 2 strain: one case of paralysis for every 2,000 infected. For every crippled New Yorker, then, there would be thousands of others who could unknowingly transmit the virus. Add to this the neighborhoods with low vaccination rates, the area could be more vulnerable than you think.

The importance of vaccination "The issue is always linked to vaccination coverage - says John Vertefeuille , epidemiologist and chief of polio eradication industry at the U.S. Centers for Disease Control and Prevention (CDC) - in this area of ​​New York, vaccination coverage is not as high as much of the U.S. population. , and the first detections in London took place in places with lower than average vaccination coverage ".

It is difficult to imagine how society - particularly the US - has been able to stop fearing this disease. Several American politicians and celebrities suffered from polio as children: Senate Republican chief Mitch McConnell, for example, or singer Joni Mitchell, who suffered a severe relapse in 1995. Baby boomers experienced the polio panic it brought the closure of schools and theaters and the emptying of swimming pools in the 1950s. "The fact that everyone had to be vaccinated was once accepted; people lined the streets to get polio and measles, mumps and rubella vaccines," says Howard Forman, physician, health policy expert and professor at Yale. School of Medicine - Over time, I believe people's memories have faded. I think now most people probably don't understand what polio is. "

If there's a silver lining to emergency, could be that of having brought the perception of the threat and unpredictable risks of polio back into the conscience of people in rich countries. From the point of view of international efforts to eliminate the disease, this can only be positive. The campaign is a shared activity by the CDC, the World Health Organization, Unicef, the Bill and Melinda Gates Foundation, and millions of volunteers from Rotary International. A reworked OPV has been launched since last year, only for the type 2 virus, which is less likely to cause mutations. Despite the entities involved, however, the campaign is chronically short of funds. New awareness could change things.

"Cases in London and New York have already brought more attention to polio and cVdpv - vaccine-derived polioviruses, said Carol Pandak, epidemiologist, global health expert and director of Rotary's PolioPlus program - They also stress the urgency to stop both wild and vaccine-derived polio, as many more people now understand that CVDPVs can cause paralysis just like wild poliovirus. polio will continue to exist somewhere, it will be a threat to the whole world. "

This article originally appeared on sportsgaming.win US.

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