TThe finding of a polio virus on repeated sampling of London’s sewerage system in 2022 is less of concern for highly vaccinated communities in the UK, where children are immune to the rare chance of paralysis. However, it is a harbinger of possible individual catastrophe for families with unvaccinated and undervaccinated children in our capital unless urgent action is taken.
In these pandemic times, we don’t have much to remember that there are some bad viruses, and there always have been. But urgent intervention to control epidemics and outbreaks with vaccines is relatively new. The devastating polio epidemics of the 1940s and 1950s, which left thousands of children in the UK paralyzed, were very much in the public eye at the time, with the familiar images of hospitals full of children in coffin-like iron lungs or paralyzed children with their legs in calipers.
These epidemics were eventually extinguished in many countries as a result of the massive deployment of two different polio vaccines by Jonas Salk and Albert Sabin. Here, the success of the polio program led to the creation of JCVI, the Joint Vaccination and Immunization Committee in 1963, and the development of a coordinated vaccination program that protects our children to this day.
In the 1980s, despite the invention of the vaccine 30 years earlier, there were still more than 300,000 annual cases of polio worldwide due to deficiencies in global coordination and lack of commitment in many countries. But as a result of enormous efforts, a remarkable impact has since been observed. Two of the three types of wild poliovirus (type 2 and type 3) have been driven to extinction by vaccine immunity; only type 1 is left. Perhaps it is possible to completely eradicate this virus from the world. And we’re almost there to see the back of it – in the last 12 months, there have been only 16 documented cases of paralytic polio caused by the residual type 1 virus worldwide. (versus 176 cases in 2019).
This success is largely due to the use of Sabin’s live oral vaccine, which everyone over the age of 18 has been given as drops by mouth or, like me, will fondly remember as a dose on a sugar cube. This vaccine is especially good at preventing the disease and stopping the transmission of the virus. It has already stopped polio in most of the world. Huge eradication efforts are underway to improve vaccination coverage in the few remaining countries where the virus is still found, with the most focus on improving access in Afghanistan and Pakistan. It’s been 42 years since smallpox was eradicated, could it be polio time? We’re not there yet and there have been some notable setbacks with business in Malawi and Mozambique over the past year, but the end of a new threat from history seems possible.
While we’re tantalizingly close to eradicating wild polio, it’s not easy. The live Sabin vaccine, which has saved the world from polio epidemics for 70 years, can very rarely undergo bizarre mutations, making it paradoxically capable of causing paralysis in undervaccinated populations. Nevertheless, the Sabin vaccine remains a critical part of the global program because of its special properties in enhancing the immune response in the gut and reducing the spread of wild polio. With polio on the decline, more attention is being paid to avoiding rare cases of paralysis caused by mutated Sabin viruses.
Perhaps counterintuitively, the most important part of the approach is to improve vaccine coverage with the Sabin vaccine, as paralysis does not occur in highly immune populations. Many countries that have eliminated the virus, mostly with the live Sabin vaccine, have switched to the Salk vaccine. The Salk vaccine contains a killed virus that cannot mutate or spread and has been part of the UK’s routine vaccination program since 2004. All children in the UK are offered five doses of the injected Salk polio vaccine during childhood.
It’s an imported Sabin virus in the London sewers that threatens children there, and the risk could be eliminated by improving vaccination coverage. Unfortunately, some of the lowest vaccine coverage in the UK is in some parts of London, right where children are at potential risk of this virus. The solution is simple, free and safe: children who have not had a dose or missed a dose should be vaccinated as soon as possible.
Polio is not the only vaccine-preventable disease, and it can strike if we drop our vigilance and lower vaccination rates. Outbreaks of measles, mumps and diphtheria have all occurred in under-vaccinated individuals in the UK over the past decade. Vaccines are extremely powerful at controlling infectious threats, but they only work if we use them.