Polio re-circulating in the West: what does transmission in New York and London imply?

Polio is circulating again in the West.

A virus that was on the way to global eradication has been detected in recent months in the wastewater of New York and London.

This is not unusual, since it can appear in the fecal remains of people vaccinated with the attenuated pathogen.

The novelty now is that there is a recorded infection in an adult in the United States, something that has not happened for a decade, and that samples from the United Kingdom suggest that local transmission has occurred, according to the European Center for Disease Control (ECDC). , for its acronym in English).

How did the virus get there?

To answer this question, it is first necessary to understand the two types of vaccines that are used: in countries where transmission is eradicated, an intramuscular vaccine is inoculated with the inactive virus, which is sufficient to prevent it from spreading when the pathogen no longer circulates in an inactive state. wild and there is a large majority of the population protected.

The second formulation is made up of oral drops with the attenuated virus, which is applied where it continues to circulate and confers protection in the blood, but, unlike the other, also in the oral and intestinal mucosa.

“With this vaccine, the immunized person would not develop the disease nor would they be able to infect others if they become infected with the wild virus,” explain researchers José Jiménez and Ana María Ortega-Prieto, from King's College London, in an article in

.

The only two countries where polio remains endemic are Pakistan and Afghanistan, with 12 cases and one so far this year, respectively.

Normally, when fecal remains are found in the wastewater, they come from the excretion of people from these countries, something that is not a major problem.

What has happened now is that beyond circulating attenuated through the drains, the virus is infecting people.

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What should the agency that manages the next pandemic look like?

It is not completely certain that this has happened in London, although the ECDC considers that “the levels of poliovirus and the genetic diversity among the isolates suggest some level of virus transmission both in the areas where positive samples were found and in the adjacent ones. ”.

Yes, it is confirmed in New York, where the identified case, which left the affected person paralyzed, is nothing more than "the tip of the iceberg," according to the United States Centers for Disease Control and Prevention (CDC). in English).

“There are a number of people in the community who have been infected with poliovirus.

Spread is always a possibility because it will be silent," a spokesman told CNN.

It is something that citizens have been able to verify during the covid pandemic: when a case is detected and its origin is unknown, it is normally synonymous with uncontrolled transmission.

"For every identified case of paralytic polio, hundreds more may go undetected," said Mary Bassett, New York State Health Commissioner, in a statement.

And this with polio is explained, in part, because the vast majority of cases are asymptomatic.

Only in about 1% of cases does the virus cause problems, when it enters the central nervous system and can cause paralysis and muscle atrophy.

What consequences can these outbreaks have?

Vaccination rates in the areas where the remains of the virus have been found are in both cases lower than in the rest of their respective countries, so the risk to their children, the main affected by this disease, increases.

In London, the authorities have already launched a vaccination campaign to inoculate a million children between one and nine years of age with booster doses.

They are all of this age, regardless of whether they already had the complete guideline.

With this they manage not to leave any out, complete the protection in children who did not have it and reinforce it in those who did.

In Spain since 1996, national coverage with at least three doses of polio vaccine has exceeded 95%, according to the Carlos III Health Institute (the guideline is considered completed with four).

The percentage of primary vaccinated children (at least two doses) rises to 98%, according to data from the Ministry of Health.

The last endemic case of polio in Spain was recorded in 1998 and since 2004 three imported cases derived from the vaccine have been detected.

Jiménez explains to EL PAÍS that with these vaccination rates, polio "should not cause problems" in Spain, where no case has been detected so far.

“The main risk group includes unvaccinated people.

There is currently no cure for polio, but fortunately it can be prevented with vaccines that have been with us for more than 60 years.

Therefore, the best way to protect against polio is to make sure that everyone, especially children under five years of age, has received the correct doses, ”he says.

The road to polio eradication

Polio travel is limited, at least in countries with high coverage.

But these cases show, at least, that the risk has not disappeared and that the goal of eradicating the virus from the face of the Earth, something that seemed within reach, is complicated.

The Global Polio Eradication Initiative (GPEI) was launched in 1988 with the aim of achieving what smallpox had been achieved a decade ago: to make it disappear.

In general terms, it can be said that the program has been a success: cases in the world have been reduced by 99% since then.

Only Pakistan and Afghanistan, where Islamic fundamentalism makes vaccination campaigns difficult, present a few cases each year.

Nigeria, the other country where there was wild polio (not transmitted by inactivated vaccines) has been since 2016 without notifying a single case.

The secret to this achievement is mass vaccination: first with the droplet vaccine and then, when the country is already free of the disease, with the injected vaccine.

Keeping levels high is crucial to shutting out the virus.

And it is something in which during the covid pandemic the guard has been lowered, either because the care systems were collapsed, for focusing the efforts of the vaccines on the coronavirus, or because of the difficulties of people to go to the health centers. vaccination due to restrictions.

According to Unicef ​​data, the level of vaccination in the world has dropped between 2019 and 2021 by 5%.

Or, what is the same: 25 million children have stopped receiving their doses.

The vaccination rate is the lowest in the last 30 years: 81% for diphtheria, tetanus and whooping cough, which are considered a good indicator of the rest of the vaccines.

In other words, even if polio is not measured, it is very likely that it has also fallen in a very similar proportion.