British health authorities have launched an urgent polio vaccination campaign targeting nearly one million children between the ages of one and nine in the London metropolitan area, after detecting the virus in a significant number of samples from wastewater.
Although there are no recorded cases of the disease, with no known cases in the UK since 1984, Government immunization advisers have recommended extreme caution, due to relatively low levels of vaccination in areas of the capital where this unusual prevalence of the virus has been identified.
In theory, the dose should be a booster for most, since the routine vaccination schedule in the UK contains five rounds against polio, in injections spread from eight weeks to 14 years.
The formula is based on an inactive variant of the virus, unlike the one still used in some countries where a live variety is dispensed, administered orally, through drops.
The advantage of this is that it offers a high degree of immunity, but, despite being safe, it has the drawback that it can be transmitted between people, in areas where the level of protection is low: the fact that it contains a live form of the virus it means that it can replicate in the digestion, although it is harmless, and be expelled in the excrement.
In rare cases, this weakened strain of the virus can be transmitted to unvaccinated people and, in the long term, this virus from a vaccine can lead to a polio-like illness that, for decades, caused severe cases of paralysis and, in most dramatic conjunctures, even death.
Experts believe this is what has led to the detection of the virus in sewage in parts of central, north and east London since February, as the samples are believed to be linked to a vaccine administered abroad.
Although it is common for a small number to be located each year, as part of the periodic reviews of the wastewater, this time there is a difference, since it is the first time that a group of genetically related samples have appeared repeatedly.
The most feasible theory is that the sample came, in the first instance, from a person who had received an oral vaccine, shortly before traveling to the United Kingdom.
As a consequence, traces of it would have reached the fecal water through the feces and, from there, it is considered probable that it has passed to other individuals, although there is no record of anyone who has requested medical assistance.
In fact, similar phenomena have occurred in cities like Jerusalem, or in the state of New York, where a young man has suffered paralysis.
The fundamental problem is that if transmission continues, there is the potential for the virus used in the vaccine to mutate and cause the more severe damage of polio again.
The United Kingdom Health Security Agency (UKHSA) acknowledges that, although many of the samples detected correspond to the safe variant of the vaccine, “some” have mutated enough to constitute a threat.
The main danger lies in the low level of immunization and the fact that the virus affects, above all, children under five years of age.
Hence, the Joint Committee on Vaccination and Immunization (JCVI), the Executive's advisory body, the same one that had supervised immunization against the coronavirus, has decided that it is preferable to include all minors up to nine years, even those with up-to-date vaccinations.
His concern is the lower level of immunization in certain demographic groups in London, well below the national average in terms of the three doses a child must have received in the first year of life (86%, compared to 92 % in the country as a whole), and even lower still in the case of booster injections, set for the start of schooling.
According to data from 2021, some 34,000 five-year-olds did not have the fourth puncture, out of a total of five.
Low immunization rates
The situation is even more complicated because these low vaccination rates coincide precisely with the areas where more samples have been detected, so the authorities trust that, by vaccinating all children, the double objective of reinforcing their protection against the most pernicious effects of the virus and, crucially, to mitigate transmission, thanks to a higher level of immunity.
In this way, in the coming weeks, the families of nearly a million children in the Greater London area will be contacted to ensure that the little ones receive this new dose, which will contain, as is usual in the United Kingdom, an inactive variety of the virus, so there is no risk of expansion.
Additionally, the authorities have decided to expand the wastewater monitoring operation, specifically in 15 points in the London metropolitan area and 10 outside the capital, in order to determine if the virus has spread to other regions.