Unheard of for almost forty years. For the first time since 1984, when the last recorded case in the UK, the polio virus has been discovered in sewage in north London. Between February and May, several samples came back positive, a sign that this pathogen is currently circulating in an area where four million people live. An alert made public this Wednesday, June 22 by the British health authorities, who take it very seriously even if no patient has yet been spotted.
This virus, which is transmitted through contaminated stool and poor hand hygiene, generally remains asymptomatic, or gives flu-like symptoms. But in rare cases, of the order of 1 in 100 to 1 in 1000, it causes paralysis which can lead to death or leave a severe handicap. No treatment exists. Seen from Europe, where it was officially declared eradicated on June 21, 2002, polio no longer seemed a threat. But its discovery in the London sewers once again reminds us of the hard-learned lesson with the Covid: “Until we are all protected, no one will be protected”.
Because this disease, which many imagined close to eradication at the global level, continues to claim victims in Third World countries. In Pakistan and Afghanistan, six children were again paralyzed last year by the so-called “wild” virus, in other words “natural” in the jargon of infectious disease specialists. If specialists insist on this term, it is because another form of this microbe, derived from strains used in oral vaccines, now causes many more cases and even epidemics, including in countries where the disease had yet been declared eradicated. Over the past three years, nearly 2,000 children have been paralyzed by viruses resulting from vaccination, according to UNICEF.
It is also viruses of this type that have been discovered in recent months in London. British health authorities believe that an individual vaccinated in his home country arrived in London carrying the microbe in his digestive tract. He was then able to infect people around him. “We are currently carrying out investigations to better understand the extent of transmission,” said Dr Vanessa Saliba, epidemiologist for UKHSA, the British health security agency, in a press release. For the moment, the treatment plant concerned covers a very large sector, and it is impossible to know more precisely which districts are concerned, or how many people are infected.
In the meantime, the authorities are calling on the British, and in particular Londoners, to check their vaccination status, and especially that of their children. Great Britain, like all European countries, indeed offers a vaccination scheme to its population which consists of three doses a few weeks apart after birth, then booster shots at 3 and 14 years of age. However, if the coverage rates reach 95% overall in the country, they are significantly lower in London, where the reminders do not exceed 71% of the children concerned. In particular, the Covid epidemic, which could disrupt the vaccination programs usually carried out in schools. Health system (NHS) officials are therefore called upon to follow up with families whose children under 5 are not up to date with their doses.
But how can a vaccine be the source of contamination? “The only product allowing the eradication of the disease is the oral vaccine, made up of a live attenuated virus. It protects against paralysis like the injectable vaccine used in Europe, but it also induces digestive immunity which prevents infection and the transmission of the pathogen by the stool. However, in very rare cases, of the order of 1 in 3 to 5 million doses administered, this attenuated virus will succeed in becoming virulent again”, explains Kamel Senouci, Deputy Director of the polio program of the Bill and Melinda Gates Foundation. The child carrier runs no risk of falling ill, but he will have the microbe in his digestive tract, which will then pass into the environment through his stools, and potentially contaminate other individuals who would not have been immunized yet.
Due to the high level of vaccination coverage, the British authorities currently consider as “very low” the risk that cases of paralysis appear in the country. Elsewhere in the world, where childhood vaccination rates are lower, and where wastewater treatment systems are less efficient or non-existent, this risk is much higher. The hope, however, remains to succeed in eradicating this disease. First, because the “natural” virus has almost disappeared, including in Pakistan and Afghanistan. “We have made unprecedented progress: for almost two years, there have been no more cases in the major cities of this region, whereas the disease was endemic there until then”, welcomes Dr Hamid Syed Jafari. , director of the polio eradication program at the World Health Organization (WHO).
The effort continues nevertheless to go to vaccinate the children in the most remote tribal zones, in spite of the security problems which undermine these regions. An essential campaign, including for the rest of the world. Just this year, a child was indeed infected in Mozambique with a virus imported from Pakistan by a traveler: “We must now make great efforts in southern Africa to prevent its wider spread”, notes Dr Hamid Syed Jafari.
In addition, a new oral vaccine has been developed to replace the one used since the 1950s. “It has been genetically modified so that it cannot become virulent again”, assures Kamel Senouci. Authorized under the WHO emergency procedure, these doses are currently deployed only in the event of an outbreak of cases linked to vaccine-derived viruses. With success: “In the fifteen countries where it has been used, all epidemics have been stopped”, continues the specialist. Elsewhere, it is imperative to continue vaccination campaigns, including for the moment with the traditional oral vaccine, in order to obtain the highest possible coverage. Because if the entire population is immunized, the virus, whether “wild” or derived from the vaccine, can no longer find anyone to infect.
But this is expensive: 4.8 billion euros are needed for the next five years. At this price only, children can be immunized everywhere in the world, and the surveillance of cases maintained. The members of the Global Polio Eradication Initiative (WHO, Unicef, Rotary International, Bill and Melinda Gates Foundation, etc.) will organize a donor meeting in Berlin this fall: “We hope that France, among others , will mobilize”, argues Dr. Hamid Syed Jafari. If the means are there, polio will become the second human disease eradicated after smallpox. There is no doubt that the British alert will help remind Western countries how important it is to fight this fight to the end.