The new cases of polio resulting from the use of the oral vaccine that have occurred in London and New York force surveillance systems to take extreme precautions. In our country this possibility is excluded because “no one with live components is used”
Just a few days ago Coordination center for health alerts and emergenciess (CCAES) directed by Fernando Simón has published an update on the risk of circulation in Spain of the polio virus following polio cases that are occurring in other countries and the detection this summer of the virus in the sewage of cities that have he had been free of polio for more than two decades, like New York or London.
The international alert for new cases in the countries around us It represents a significant change in trend in the long-awaited path towards the eradication of the disease, which it had begun to glimpse in 2020 and which is now putting the entire international community under control.
The CCAES recognizes in its new risk assessment that “the probability of introducing the poliovirus in our country is considerable” but at the same time he believes that “the current high level of immunity” of the Spanish population “would minimize the possibility of transmission and circulation of the poliovirus in the population”. Furthermore, according to the agency, even if the virus were to return to circulate, given “the high quality of the epidemiological surveillance system for polio and the high standards of environmental sanitation and water treatment, this possible introduction would have a minimal impact. therefore the The risk associated with poliovirus in Spain is currently considered very low “.
However, the Coordination Center for Health Alerts and Emergencies has urged to strengthen surveillance systems, monitor polio vaccination coverage ratesidentify pockets of susceptible population and urge people who will travel to areas at risk of polio virus transmission to go to international vaccination centers before traveling, among other measures.
What is the risk of polio virus infection?
Polio is caused by poliovirus infection. Although there are three types of this pathogen (PV1, PV2 and PV3), two of them are considered to be already eradicated and only the so-called PV1 is in circulation. Humans are the only known reservoir of poliovirus and transmission occurs directly from person to person via the fecal-oral route or by the respiratory route through pharyngeal secretions, although it can also be transmitted indirectly through fecal contamination of drinking water and food.
More than 90% of infections are asymptomatic. in 4-8% they cause malaise, vomiting or headache and in less than 1% aseptic meningitis can occur and, in 1 case out of 200, acute flaccid paralysis (APA) It primarily affects the extremities, but can also affect the respiratory muscles and cause death.
Since when have there been no cases of polio in Spain?
The last case in Spain of p. virus poliomyelitiswild oil was produced in 1988. There have been four cases of paralytic poliomyelitis in Spain since that date, but all associated with the vaccine or vaccine-derived poliovirus.
In which countries are there still cases of polio?
Both Spain and the World Health Organization’s European region have been certified as a polio-free region since 2002. In 2020, only two countries in the world had active transmission of the wild poliovirus: Pakistan and Afghanistan.
However, several cases of paralytic poliomyelitis have been detected since 2021 in countries that have not reported cases since at least 2016, such as Malawi, Mozambique, Israel, Ukraine and the United States. In the UK, US and Israel they have detected the circulation of vaccine-derived poliovirus in their wastewater.
Can vaccine-associated polio cases occur?
“There is no live vaccine used in Spain that could cause a vaccine polio case. All vaccines used in Spain are inactivated and cannot cause contagion,” he explains. Amés García, president of the Spanish Society of Vaccinology.
The international cases of polio that are occurring associated with vaccines are due, as explained by Jess Castilla, member of the vaccination working group of the Spanish Society of Epidemiologybecause “vaccines can be inactivated or with live viruses. Up until 2004, the oral vaccine containing live viruses was used in Spain. This live virus vaccine has some advantages: it generates a more complete response and also immunizes the environment.” of the vaccinated person, but there is a risk that in an environment where someone can be immunosuppressed, the person could get sick “.
Castilla explains that “to avoid this risk in Spain and other countries have eliminated the use of the oral vaccine and they opted for the injected vaccine, the inactivated one, which is safer. However, in endemic countries or where the injected vaccine is very expensive, the oral vaccine is still used and this means that the vaccine virus of the oral vaccine can be detected in the wastewater of some countries or, in its case, reach Spain “
All in all, in his view, these oral live virus vaccines “in principle shouldn’t be a big deal because these vaccines had been widely used until 2004 and there weren’t even a large number of cases, but it’s true that , although rare, this possibility exists “.
Will it be necessary to revaccinate the population against the polio virus?
The CCAES does not consider in its risk assessment actions such as that taken in the UK to urgently vaccinate all children aged 1 to 9 in the London metropolitan area.
“Among us This reconquest process does not seem necessary Why do we have Very high vaccination coverage, close to 95% and much higher than those of other countries in our own socio-economic context and this has been the case for many years “, explains Amés García, president of the Spanish Society of Vaccinology.
Jess Castilla, a member of the vaccination working group of the Spanish Society of Epidemiology, does not believe that a re-vaccination or extra campaign is necessary to win back the population: “Vaccination rates are very high. The challenge is not to reduce vaccination coverage and, in the case of people who come from countries in conflict where there have been gaps in vaccinations, try to catch them up and include them in our vaccination programs, “he says in relation to countries like Pakistan, Afghanistan or Ukraine, among others.
Can the polio virus change and are current vaccines no longer effective?
“The performance of the polio virus has nothing to do with that of SARS-CoV-2. There are several types of poliovirus circulating right now, but there is one that is clearly predominant and vaccines have a very clear impact on the type of poliovirus circulating, “explains Amés García, president of the Spanish Vaccination Society.
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