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Monday, November 28, 2022

Should we be concerned about recent polio outbreaks?

On September 9, New York State Governor Cathy Hochul declared a “state of emergency due to disaster” due to the polio outbreak. The outbreak included a single case of flaccid paralysis (PFA), but also the widespread spread of vaccine-derived poliovirus (CVDPV) in sewage from several counties in the state. Everything indicates that its circulation must have expanded from at least April 2022.

The return of a wiped out virus?

The United States joins a relatively short list of more than 30 countries thanks to global efforts to eradicate polio. Afghanistan and Pakistan are the only endemic countries with “wild” virus outbreaks, but several African countries, and some eastern Mediterranean and Europe, have outbreaks of vaccine-derived poliovirus.

Without going further, Israel received a case of polio in February. And in London and Northern Ireland, still without clinical cases, sewage suggests CVDPV to be widely circulated.

Genomic analysis indicates that viruses from all three countries are closely related. Both the WHO and the European Center for Disease Prevention and Control (eCDC) have expressed concern about the risk of the virus re-emerging in countries where it has been eradicated and monitor the development of these outbreaks. .

How the attenuated virus in a vaccine can mutate and make us sick

Attenuated oral polio vaccine virus (although very rarely) can mutate into VDPV. To understand what’s going on, it’s important to first know that the vaccine virus is excreted in feces and spreads from person to person. This is an advantage of the oral vaccine, as it helps protect unvaccinated people.

Well, in populations with low vaccination rates, the vaccine virus is transmitted between uninfected people for a long period of time and, although this is not common, it sometimes turns into forms capable of causing disease (flaccid paralysis, wild poliovirus). similar to) and spread to the community.

In most cases, these infected are asymptomatic. But if they reach a place where there is a large number of illiterate population, CVDPV will eventually infect them.

It should not be forgotten that the polio virus, mainly of oral-fecal transmission, is easily transmitted. Irrigation water, especially in countries with poor sanitation or contaminated with wastewater. An immunocompetent infected person can outgrow the virus for 3-6 weeks. An immunosuppressed person does it for a long time.

Fortunately, very few (about 1 in 150-200 infected) will develop some form of flaccid paralysis. But they will infect each other and continue transmission (and risk additional paralysis) for quite some time.

Spain has only 4 cases of polio in 30 years

In Spain, polio cases declined sharply with the introduction of the oral vaccine in the late 1960s, and the last endemic case occurred in 1988. Formally, polio has been eradicated from our country for decades and since 2004 it has been administered using an injectable vaccine, which cannot produce cVDPV.

Only 4 cases of polio have been reported in the last 30 years. All vaccine-derived viruses by and possibly imported. In three of them infants (in 1999, 2001 and 2005). The 2005 case infected 3 close contacts who were not paralyzed.
The fourth case, most recently, from 2019, was of a 26-year-old immunocompromised adult who was not paralyzed. The patient was isolated and confirmed virus excretion for a few months, although there was no new infection, not even from his direct contact (vaccination). This last case was the core of an assessment of the risk of the virus re-emerging in Spain by the Ministry of Health’s Coordination Center for Health Alerts and Emergencies (CCAES).

Epidemiological surveillance of poliovirus in Spain

  1. Maintenance of high immunization coverage, including identification and action of travelers in vulnerable populations and countries at risk.
  2. Strengthening epidemiological surveillance.
  3. Response plan for the detection of poliovirus.

The high vaccination rate (at least 95% of the population) is the main action against poliovirus. In Spain, these figures have been reached since the late 1990s. Higher figures do not suggest that rates are lower in certain places or certain social groups. And they can be reduced to some extent during the pandemic.

Cases of poliovirus in Spain are difficult to go unnoticed because all acute flaccid paralysis (AFP) in children under the age of 15 are monitored and, in addition, there are nine laboratories that periodically collect diagnostic information from patients. The samples are analyzed to verify their absence. poliovirus.

A third tool is poliovirus surveillance in wastewater, which is still in its infancy in Spain. In 2019 it covered 7-8% of Spain’s population and all samples taken were unlikely to contain poliovirus.

The risk in Spain is negligible

As noted in the 2019 CCAES report, “Spain is likely to introduce wild, vaccine or vaccine-derived polioviruses as long as the poliovirus is in circulation in the world.” However, the document states that “high vaccination coverage, quality of surveillance systems and high ability to detect and respond to potential poliovirus-related incidents in our country, coupled with high standards of environmental sanitation, make the risk associated with it.” They are rarely considered in Spain.

And it’s true: the risk of an outbreak in Spain is very low. But the possibilities have (somewhat) increased in recent times. Recent population movements across Europe from countries with less vaccination (Ukraine, Afghanistan, etc.), immigration from countries with outbreaks, travel from Spain to those countries and, above all, the presence of outbreaks in neighboring countries alert us. done.

Pre-alert does not mean a booster dose in the pediatric population, as in the UK, where the virus is widely spread in sewage and has a high proportion of unvaccinated. But it strengthens action to meet coverage and incomplete vaccination guidelines. Also expand and strengthen the quality of syndromic surveillance of flaccid paralysis. And, also, and perhaps above all, the expansion and improvement of wastewater monitoring, especially in neighborhoods or areas where populations at particular risk live because of low vaccination rates.

In a certain way, it is about maintaining (and improving to some extent) what has been done over the years and how well it is producing results so far. For parents concerned about their children, vaccination is the answer.

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