Poliomyelitis: Current Epidemiological Situation in the World and in the Gaza Strip

by Prof. Hervé Fleury, MD-PhD | Ventum Biotech Scientific Board Member

Introduction

Poliomyelitis is a very old disease whose clinical presentation was made for the first time in 1789 in England ("Debility of the lower extremities"); J. Von Heine in 1840 put forward the hypothesis that the disease could be infectious; in 1894 the USA experienced its first major epidemic; Landsteiner and Popper in Vienna put forward the hypothesis of a virus, which was confirmed by the isolation of 3 antigenically different viruses in 1931 (Burnet and McNamara). In 1948, Weller and Robbins succeeded in growing these viruses in human cells and thus paved the way for a vaccine; it was in 1958 that Jonas Salk developed a vaccine called "Killed or Inactivated" because the three viruses had been cultured and then chemically inactivated and therefore no longer had any infectious power. I had the honor of meeting J. Salk at an AIDS conference in Stockholm in 2008; he had started a vaccination trial against HIV and with Dominique Dormont (a great figure in French Virology) we had considered joining in. A second vaccine (Sabin's) appeared in 1961 and was composed of 3 live attenuated strains of virus. 

Although the disease was now well known in European countries and the USA, it became apparent in the 1970s that it was of considerable importance in developing countries and led the WHO to launch a global vaccination program in 1974.  In 1988, an initiative of Rotary International strengthened the fight against the disease. This gradually disappeared after very large-scale vaccination campaigns (example: 575 million children vaccinated in 2001 in 94 countries including Pakistan and Afghanistan).

In 2003, vaccination campaigns were interrupted in the northern part of Nigeria following unfounded rumors and the circulation of the virus was re-initiated. Quickly, apart from Nigeria, Afghanistan, Pakistan and India were involved. Between 2009 and 2010 there were epidemics that were quickly brought under control in Guinea, CAR, Côte d'Ivoire, Kenya, Tajikistan and Congo. There have been some very great successes such as the proclamation of the last case in India in 2011.

The last case of poliomyelitis occurred in the European zone in 1998.

Poliomyelitis and its pathophysiology

The three poliomyelitis viruses belong to the Enteroviruses; the viral reservoir is strictly human; the infected man emits the virus in the stool and transmission is either directly human (airborne, dirty hands) or indirect (dirty water, fruit or vegetables sprayed with dirty water, shellfish that have concentrated the viruses present in the water). This cycle of transmission is favored by the survival of the virus in the external environment.

The virus, introduced orally, will multiply in the tonsils as well as in the lymphoid formations of the digestive tract that it will be able to pass through because it is resistant to the fat solvents present in the digestive ferments. During a passage through the bloodstream, the virus can reach the neurons of the spinal cord and induce inflammation or even neuronal destruction that causes paralysis.

Incubation is 10 to 14 days; Then appear fever and muscle pain and, more rarely, sudden paralysis most often affecting the lower limbs, but this paralysis can be ascending and affect the respiratory centers, hence these particularly poignant images of children on artificial lungs, particularly in the USA in the 50s.

Why new epidemics?

First of all, let's come back to vaccines; the killed vaccine is and has been the preferred vaccine in industrialized countries such as Europe and the USA; It is administered by injections and induces neutralizing antibodies that protect against nerve damage. But they do not give digestive immunity and do not prevent viral circulation in a community.

The attenuated vaccine is administered orally and has been favored in areas such as Africa because mass campaigns were needed; In addition, digestive immunity is obtained and viral circulation decreased between individuals in a given area.

So, what are the reasons for a resurgence of poliomyelitis; first, the circulation of "Wild" viruses has resumed in some areas; for example, the circulation of Wild Poliovirus 1 (WPV1) has resumed in countries such as Pakistan and Afghanistan. On the other hand, one of the attenuated vaccine strains circulating in the general population "Circulating vaccine-derived poliovirus type 2 (cVDPV2)" is likely to return to the wild virus by simple mutation and induce cases of disease. This is what is currently happening in Niger, Benin, Guinea, Indonesia, Nigeria, Somalia, Sudan, Yemen (non-exhaustive list). In 2022, the United States experienced a case of cVDPV2 poliomyelitis in a New York subject who had not been vaccinated with the inactivated vaccine. More rarely, it is the type 1 vaccine strain that is concerned (cVDPV1) as in the DRC. In the European zone, cases of poliomyelitis linked to cVDPV2 have been observed in Ukraine. Similarly, cases of cVDPV3 infections have been reported from Israel.

The situation in Gaza

Among the technical advances in environmental virology, it is worth highlighting the detection of viral genomes by PCR in wastewater. Many countries use this detection, which was developed during the SARS-CoV-2 pandemic. For example, the USA has shown that it has cVDPV2 in the wastewater of New York.

This is how the cVDPV2 virus was detected in Gaza's wastewater where vaccination coverage has decreased since 2022 from 99% to 89% and taking into account the very degraded public hygiene situation in the area, the WHO fears the appearance of poliomyelitis cases among Palestinian children. The envisaged response is the use of 1.6 million doses of a next-generation attenuated strain nOPV2 (with a very low possibility of resurgence to the wild strain) in the Gaza Strip before the end of the year and if possible, in September-October 2024.

References: CIDRAP (University of Minnesota), Human Virology (H. Fleury, Masson publisher, 2009), Polio Global Eradication Initiative, CDC (USA), eCDC