What is known about the situation in French Guiana?

As part of a research project coordinated by ANRS-MIE, polioviruses derived from the Sabin type 3 vaccine strain (PVDV 3), with a similar genetic profile, were detected in wastewater samples collected between May and August 2024 at several wastewater treatment plants in French Guiana (Cayenne, Saint-Georges, and Remire-Montjoly).

Genetic analyses of these samples conducted by the National Reference Center for Enteroviruses and Parachoviruses (Institut Pasteur Paris) show that the viruses have sufficient mutations (more than 10) compared to the strain contained in the oral vaccine to be considered a strain derived from the Sabin 3 vaccine strain (PVDV 3), and that they are genetically related to one another. These genetic analyses also indicate that these strains should be considered wild poliovirus strains since they could cause paralysis.

These strains have not yet been identified in other countries. In French Guiana, although no cases of polio have been reported to date, the detection of these strains in samples from different locations at least two months apart confirms human-to-human transmission—without ruling out transmission outside of French Guiana—and their classification as circulating poliovirus cPVDV3 according to the World Health Organization.

Santé publique France is assessing the risks of contracting polio for the population and is strengthening its surveillance system in collaboration with the ARS Guyane and its partners.

Why are polioviruses detected in wastewater?

When a person is infected with poliovirus, the virus multiplies in the intestine and is excreted in the stool. The viral particles present in the stool then end up in the wastewater. Since most poliovirus infections are asymptomatic, wastewater surveillance can help detect the circulation of the virus even before a case of paralysis appears.

In France, this surveillance was operational from 1973 to 2018 at four wastewater treatment plants in the Île-de-France region, but it was discontinued at the end of 2018 due to low poliovirus detection rates and high vaccination coverage.

This is the first detection of circulating VDPV in a region of France since the 2000s. These detections indicate silent circulation of VDPV3 within a population in French Guiana with insufficiently vaccinated subgroups.

What is the source of these viruses?

Since the oral vaccine is not used in French Guiana, these vaccine-derived viruses were imported by one or more individuals who received the oral vaccine abroad, and person-to-person transmission may have been facilitated within under-vaccinated population groups. It should be noted that the oral polio vaccine (OPV) is still used in some South American countries.

Although the Americas region has been considered free of circulating poliovirus since 1994 by the WHO, this detection has international implications. Consequently, the Pan American Health Organization (PAHO) has since reminded all countries in the Americas region of the importance of strengthening surveillance for flaccid paralysis in children as well as in adults, and of achieving high vaccination coverage (95% with 3 doses). Furthermore, the ECDC has endorsed the WHO’s temporary recommendations for EU/EEA citizens residing in or visiting French Guiana for an extended period (>4 weeks): an additional dose of the poliovirus vaccine must be administered between four weeks and 12 months prior to international travel. Travelers to French Guiana must be vaccinated in accordance with their national vaccination schedules.

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What is the risk to the population of French Guiana?

Regardless of the geographic origin of these viruses, the currently clinically silent circulation of PVDV3 in the Cayenne metropolitan area and in Saint Georges is associated with a low risk of paralytic forms (8 out of 10,000 infected people for type 3 viruses, varying by age; a lower risk than for type 1 viruses, for which it is estimated at 1 in 200) of developing poliomyelitis among unvaccinated or inadequately vaccinated individuals, particularly children, infants, and immunocompromised individuals.

The risk of developing severe neurological forms, however, is extremely low for people who are up to date on their vaccinations.

In French Guiana, despite a diverse range of vaccination services provided by various entities (private sector, Maternal and Child Health Centers, Decentralized Prevention and Care Centers, local hospitals, and associations), vaccination coverage is lower than in mainland France, with under-vaccinated population groups, particularly in isolated areas. Insufficient vaccination coverage, combined with precarious living conditions or overcrowding (community living) that facilitate the virus’s primarily fecal-oral transmission through direct contact (dirty hands or contaminated objects) or via a contaminated environment (sewage, food), or through direct respiratory transmission, increases the risk of developing polio as well as human-to-human transmission of poliovirus.

What recommendations and measures have health authorities put in place?

In response to the situation, several measures are being implemented by health authorities in collaboration with healthcare professionals:

• Launch of a catch-up vaccination campaign:

  • In schools, led by the ARS, to vaccinate children and adolescents who are unvaccinated or whose vaccinations are not up to date for all mandatory vaccinations in schools in Cayenne, Rémire-Montjoly, Matoury, and St-Georges de l’Oyapock.

  • Outside of schools to vaccinate, in particular, infants and children not enrolled in childcare facilities who are not up to date on their vaccinations, again within the geographic area covered by this screening.

  • All healthcare professionals in French Guiana authorized to administer vaccines are also urged to verify the vaccination status of their patients throughout the territory, particularly children and immunocompromised individuals, and to administer catch-up vaccinations if necessary.

• Raising awareness among healthcare professionals regarding the risk of polio cases, with a reminder of the protocol to follow in the event of suspected polio, including the collection of appropriate samples for genome detection via PCR and/or culture (2 stool samples collected 24 hours apart) by the National Reference Center (NRC) for enteroviruses and parechoviruses, and for differential diagnosis (nasopharyngeal swab, blood) by the NRC or any other clinical laboratory.

• Establishment of a one-year environmental surveillance program for wastewater: the Pasteur Institute of French Guiana, which is already responsible for the physicochemical monitoring of wastewater, will also screen for the poliovirus during this period in collaboration with the National Reference Center (CNR) for Enteroviruses at the Pasteur Institute in Paris, which is also a WHO Collaborating Center. This one-year study is intended to determine the extent and evolution of poliovirus circulation in wastewater and to draw conclusions regarding public health management. It will verify whether the measures implemented are effective in stopping the circulation of these poliovirus strains in French Guiana and will help decide on any additional actions to be taken.

In addition, it is important to note that the risk of contamination can be reduced by following standard hygiene practices (washing hands with soap before preparing meals, before eating, and after using the restroom, and by washing and peeling fruits and vegetables before eating them).