Origin of the virus, vaccination… What you need to know about this disease – Libération

The war between Hamas and IsraeldossierA case of polio was confirmed on Friday, August 16, in a baby in the center of the Palestinian enclave, where the war prevents vaccination and has caused a catastrophic deterioration in hygiene conditions, favoring the circulation of the virus.

Polio, a disease that can leave patients, especially children, permanently disabled, has largely disappeared from the world thanks to vaccination. But it remains and regularly threatens to resurface, as in Gaza where the first case was confirmed on Friday, August 16, for the first time in a quarter of a century.

A dangerous virus…

Poliomyelitis is a disease caused by a virus, the poliovirus. Most of the time, it remains in the digestive system and causes few, if any, symptoms. But sometimes it migrates to the brain and can lead to more or less severe paralysis of certain limbs. This paralysis may never resolve.

The risk is, in itself, low: about 1 in 200. But it is multiplied on a collective scale by the highly contagious nature of the virus, especially since no treatment can interrupt the infection. For decades, this situation has made polio one of the most threatening diseases for children, likely to remain disabled for life, although adults can also be seriously affected.

…but almost eradicated

A widespread threat just forty years ago, polio has now largely disappeared from the world, particularly from Africa. “Cases due to wild poliovirus have declined by more than 99% since 1988, from 350,000 cases in more than 125 countries to six cases reported in 2021,” summarizes the World Health Organization (WHO).

These latest cases are concentrated in two countries, Afghanistan and Pakistan, which have not yet succeeded in blocking the circulation of the virus on their territory.

This does not mean, however, that polio is absent from other countries. About thirty of them have had cases of the disease in recent years. But they were either directly imported from countries where circulation is still active, or linked to vaccination. There is indeed a very slight risk with certain polio vaccines.

The success of vaccination

In any case, it is thanks to vaccines that the virus has largely disappeared. Campaigns have been organized, under the aegis of the WHO, for decades throughout the world. They sometimes come up against local resistance, as in Pakistan where vaccinators are regularly assassinated, particularly against a backdrop of rumors of espionage.

Health authorities are also faced with the difficulty of explaining that a small risk is associated with one of the types of vaccine used, called attenuated. This vaccine, which uses a virus made less aggressive, can, in one case in several million, cause an infection. Given the risks represented by the disease, the benefit of this vaccine is therefore beyond doubt. The other type of vaccine, called inactivated virus, is preferred because it does not represent any risk of infection.

Regular reappearances

Although polio has largely disappeared, it is still far from being a thing of the past and remains a major public health concern. “As long as there is even one child infected with poliovirus, children around the world will be at risk of contracting the disease,” WHO points out. This virus “can easily be imported into a polio-free country and then rapidly spread through populations that have not been immunized“, adds the authority.

This threat is not limited to poor countries. In 2022, the virus was detected in sewage in New York, USA, and London, UK. This detection does not necessarily mean that the disease will reappear there. A case was reported at the time in New York, but there were none in London. However, the British authorities were able to organize a large vaccination campaign among children.

The case of Gaza

The situation appears different in Gaza, where in addition to the problem of vaccination, the catastrophic deterioration of hygiene conditions also favors the circulation of the virus. It was detected in wastewater in July, before the confirmation of a first case on Friday, August 16, the first in 25 years, following analyses of stool samples from three Gazan children. “presenting with suspected acute flaccid paralysis, a common symptom of polio” at the Jordanian national polio laboratory. According to the Palestinian Ministry of Health, this is a “10 month old baby who had not been vaccinated”, found in Deir El-Balah, in the centre of the besieged Palestinian territory.

Hours earlier on Friday, UN chief Antonio Guterres had called “all parties to immediately provide concrete assurances guaranteeing humanitarian pauses for the campaign” of vaccination.

Before him, the World Health Organization (WHO) and UNICEF had called for humanitarian pauses “seven days” to enable two vaccination campaigns for more than 640,000 children under ten years old. These two series “should be launched in late August and September 2024 across the entire Gaza Strip to prevent the spread of the variant currently circulating”known as cVDPV2, the two agencies said. More than 1.6 million doses of the nOPV2 vaccine are expected to be delivered to Gaza by the end of August, the statement said.

The UN stresses that vaccination coverage must be at least 95% in each vaccination campaign to prevent the spread of polio, “given that health, water and sanitation systems are seriously disrupted in Gaza”.