The World Health Organisation (WHO) has declared a national emergency as several samples of live vaccine-derived polio have been found circulating in London sewage systems. It is believed that the detected strain originated from an individual who was vaccinated with the live oral polio vaccine abroad. If this strain continues to circulate, it can mutate into vaccine-derived polio, which could cause significant morbidity and mortality in unvaccinated children.
With this in mind, the Joint Committee on Vaccination and Immunisation (JCVI) has advised that a targeted inactivated polio vaccine (IPV) booster dose should be offered to all children aged one to nine years across London. If engagement with the booster campaign is high, herd immunity will be met in areas with low vaccine coverage and there will likely be no cases of polio in the UK. If engagement remains low, however, the poliovirus will continue to circulate and there could be a re-emergence of polio within, and potentially outside, London.
Polio, or poliomyelitis, is a contagious viral illness that is transmitted through contact with infected faecal particles, or via droplets from an infected sneeze or cough. The virus mainly affects children, and although 70% of infected children are asymptomatic, they can still transmit the poliovirus (according to the CDC). Most symptomatic children will present with flu-like symptoms, muscle weakness and paresthaesia (pins-and-needles sensations), but around one in 200 infections leads to irreversible paralysis – of these, 5–10% of cases are fatal following paralysis of the individual’s breathing muscles.
The last case of polio in the UK was detected in 1984, which is attributed to the rollout of the inactivated-polio vaccination program in 1956. But with the vaccine-derived virus circulating in sewage systems, cases of polio could manifest if the population is not protected from the virus.
The WHO states that 80% polio vaccine coverage is required to achieve herd immunity. GlobalData epidemiologists forecast that 83.32% of children aged five in the UK will have received four or more doses of the polio vaccine by the end of this year. However, there is significant geographic variation in vaccination coverage. According to the childhood vaccination coverage statistics, published by National Health Service (NHS) Digital in June this year, areas of London, such as Hackney, have much lower engagement – with approximately 68% of children receiving the necessary number of vaccinations.
It is also expected that vaccination coverage estimates from GlobalData may fall below the actual coverage due to the impact of the coronavirus disease 2019 (Covid-19) pandemic. Routine vaccination appointments were majorly disrupted during this period, and individuals were reluctant to attend healthcare facilities due to fears of coming into contact with Covid-19. But as the healthcare system returns to pre-pandemic service, it is of paramount importance that parents are encouraged to engage in all vaccination programmes so that herd immunity is established in all areas of the UK.
A further 15 sites in London started sewage sampling last month, and ten to 15 sites will be set up across the nation to determine if poliovirus is spreading outside of London. GlobalData epidemiologists expect that if the booster campaign is a success, and take-up is high, there should be no further cases of polio in the UK and circulation of the virus should decline. But if engagement remains low in boroughs like Hackney where the virus is circulating, there is potential for the virus to mutate and cause cases of polio in the unvaccinated population.