Polio: A re-emerging global health threat

Bette Browne reports on the re-emergence of polio and the complexities of the struggle against the disease.

The eradication of polio from Ireland and most other parts of the world was a triumph for medicine. However, there is growing concern about the disease re-emerging in New York, London, and Jerusalem, with some health officials warning this could be the “tip of the iceberg”. 

The re-emergence of cases has been a wake-up call to the medical world. In 1988, health and aid organisations poured billions into the Global Polio Eradication Initiative (GPEI) and, since that time, cases of the disease have fallen dramatically from 350,000 to about 240 so far this year. In 2022, the cases have mainly arisen in Pakistan and Afghanistan, while there is still a risk of infection in parts of Africa and some Middle Eastern countries. 

The countries that have had enduring cases of the disease have extremely low vaccination levels because of inadequate healthcare facilities, poverty or conflict. However, now cases are emerging in countries where it was believed the disease was eradicated. 

Re-emergence 

In March, Israel reported its first case since 1988. In June, British authorities discovered the virus in sewage, though no infections in people were identified. The UK government said all children in London aged one-to-nine would be offered a booster shot. 

In July, US health officials detected the virus in an unvaccinated man in his 20s who was diagnosed with paralytic polio in Rockland County, New York. 

The cases in Jerusalem, New York, and London are all derived from the oral polio vaccine and appear to be genetically linked, according to the World Health Organisation (WHO). 

“The virus detected in environmental samples in New York is genetically linked to viruses detected in sewage samples from London and in sewage samples collected between January to June 2022 from Jerusalem,” the WHO stated on 14 September. 

While all are derived from the oral polio vaccine, experts say the problem lies not with the vaccine itself, but with low vaccination coverage. Small groups of families in New York, for example, have not vaccinated their children against the virus and one such group is within the ultraorthodox Jewish community in Rockland County. 

“Vaccine-derived polio virus is a well-documented type of polio virus that has mutated from the strain originally contained in the oral polio vaccine (OPV). The OPV contains a live, weakened form of polio virus,” the WHO said. “On rare occasions, when replicating in the gastrointestinal tract, OPV strains genetically change and may spread in communities that are not fully vaccinated against polio.” The US Centres for Disease Control and Prevention (CDC) noted that “even a single case of paralytic polio represents a public health emergency in the United States”. 

The level of concern increased further after a statement from a top health official in New York. “Based on earlier polio outbreaks, New Yorkers should know that for every one case of paralytic polio observed, there may be hundreds of other people infected,” New York State Health Commissioner Ms Mary Bassett said on 5 August. “Coupled with the latest wastewater findings, the department is treating the single case of polio as just the tip of the iceberg of much greater potential spread.” 

On 13 August, a CDC official sounded a similar warning. The case first identified in New York in June was “just the tip of the iceberg” and an indication there “must be several hundred cases in the community circulating”, Dr José Romero, Director of the CDC’s national centre for immunisation and respiratory diseases, told CNN. 

On 9 September, New York Governor Kathy Hochul declared a state disaster emergency to free-up more resources and expand the number of polio vaccine administrators after the virus was detected in wastewater from four other New York counties. 

If a vaccine-derived polio virus strain is allowed to circulate among unvaccinated populations for long enough, the weakened virus can revert to a form that causes illness and, in some cases, paralysis, the CDC warned. 

UK 

The UK Health Security Agency (UKHSA) stressed that in the UK most people were protected by vaccination. “No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low,” Dr Vanessa Saliba, Consultant Epidemiologist at the UKHSA, tweeted on 5 September. 

Wild polio virus (WPV) is the best-known form of the disease and has been eradicated from most countries, with the exception of Pakistan and Afghanistan. However, vaccine-derived poliovirus (cVDPV) has been increasing in recent years, particularly in Africa and Asia, due to low immunisation rates and the impact of Covid-19. 

The vaccines to combat the disease come in two types: The Jonas Salk injectable polio vaccine (IPV), made in 1954 with a ‘killed’ virus; and the Albert Sabin oral polio vaccine (OPV), made in 1960 with a live, but weakened virus, often called the ‘sugar lump vaccine’. This latter vaccine is the one at issue in the current resurgence. 

By the early 1970s most of the world was using this oral vaccine, but today many countries (including Ireland, the US and the UK) no longer do so. In 2001, the injectable IPV vaccine replaced the routine use of the OPV vaccine here. 

Ireland 

The first polio epidemic in Ireland occurred in 1942. The incidence of the disease fluctuated during the following years with epidemic waves in 1947, 1950, and 1953. The last major polio epidemic was in Cork in 1956. 

Cases of polio in Ireland fell when the vaccine was introduced in 1957 and the last recorded case of polio was in 1984. “But the infection is still found in some parts of the world. Because of this, there is a very small risk that polio could be brought back to Ireland,” according to the HSE website. 

In his 2006 memoir The Broken Boy, journalist Patrick Cockburn recounted his experience of contracting polio at the age of six, while living in Youghal, Co Cork. His brother Andrew, who was three years older, also contracted the disease. 

Cockburn describes how frightening it was for young children to be taken away from their parents and siblings and placed in isolation. Treatment often meant being placed in a respirator known as an ‘iron lung’, which enclosed most of the body. “It was terrifying to be in the iron lung. One girl in St Finbarr’s (Hospital) was put into an iron lung and she compared it to being buried in a coffin,” Cockburn recalled. 

In Ireland today, memories have dimmed about the severity of the disease, which by the 1950s killed or paralysed over half a million people around the word every year. But the consequences of polio still blight the lives of thousands who suffer from the devastating effects of post-polio syndrome. In Ireland alone, as many as 7,000 polio survivors are living with disabilities from the late effects of the disease. 

The charity Polio Survivors Ireland says about 40 per cent of polio survivors are experiencing a range of disabilities. Many have had years of rehabilitation to help regain independence, only to find their mobility affected in later life by post-polio syndrome. This is a neurological condition resulting in new symptoms in people who had polio, but whose condition has been stable for at least 15 years. It can occur from 20-to-40 years after the initial illness. 

Post-polio syndrome may cause sleep impairment, fatigue, new muscle weakness, muscle and joint pain, wasting of muscle, a severe intolerance to cold, speech difficulties, difficulty swallowing, and respiratory problems. Many people end up needing mobility supports. 

“Polio is gone,” Polio Survivors Ireland says, “but the legacy of polio is the ongoing support and help required by polio survivors.” 

The campaigns to combat the re-emergence of the disease in London and New York will use the injectable vaccine. If further wastewater testing suggests that the polio virus has continued to spread, experts say it might be necessary to examine other options, one of which might be an emergency vaccine. 

Vaccination 

In 2020, the WHO listed a new polio vaccine for emergency use. This vaccine, which contains a live, but weakened virus that scientists believe is less likely to mutate into a dangerous form, performed well in clinical trials and was approved for emergency use by the WHO in April 2022. About 265 million doses are now being rolled out in 14 countries, primarily in Africa. 

Infections from the OPV oral vaccine are appearing at a time when cases caused by the wild or naturally circulating virus continue to plummet. Since 2017, there have been 396 cases of polio caused by the wild virus, against more than 2,600 linked to the oral vaccine, according to the WHO. If a population is adequately immunised, however, it will be protected against both wild and vaccine-derived viruses. 

The oral vaccine has been used because it is cheap, easy to administer and better at protecting entire populations where polio is spreading. But it can also cause polio in about two-to-four children per two million doses. In extremely rare cases, the weakened virus can also sometimes mutate into a more dangerous form and spark outbreaks, especially in places with poor sanitation and low vaccination levels. 

These outbreaks typically begin when people who are vaccinated shed live virus from the vaccine in their faeces for many weeks afterwards. The virus can then spread within the community and, over time, turn into a form that can paralyse people and start new epidemics. 

Many countries that eliminated polio switched to injectable vaccines containing a killed virus decades ago to avoid such risks. The Nordic countries and the Netherlands never used the oral vaccine. The goal is to move all countries to the injectable vaccine once wild polio is eradicated, but some scientists argue that the switch should happen sooner. 

Global Polio Eradiation Initiative 

On 26 April 2022, the GPEI launched an ambitious strategy to eradicate all forms of polio in the world by 2026. However, to fully implement its aim of a polio-free world, it will need urgent additional funding of €4.8 billion. The GPEI’s goals include vaccinating 370 million children every year for the next five years and continuing global surveillance activities for polio and other diseases in 50 countries. 

“Polio is a highly infectious disease, and if we did not know it before Covid-19, we certainly know now how quickly infectious diseases can spread globally. If we do not eradicate polio, this virus will resurge globally,” according to polio expert Mr Aidan O’Leary, originally from Ireland, who took over last year as WHO Director for Polio Eradication. 

Mr O’Leary told the Gavi Vaccine Alliance’s Polio News: “My priority, and all of our priorities, must be simply this: Find and vaccinate every last child. If we do that, polio virus will have nowhere to hide. That means finding out where those last remaining unreached children are, and what obstacles stand in the way to vaccinating them. Is it because of lack of infrastructure? Insecurity or inaccessibility? Lack of proper operational planning? Population movements? Resistance? Gender-related barriers? If we can identify the underlying reasons, we can adapt our operations and really zero-in on those last remaining virus strains.” 

However, the battle against polio suffered a serious setback during Covid-19 when health workers and resources were focused primarily on the global struggle against that disease. According to WHO/ UNICEF data, 23 million children missed out on basic vaccines through routine immunisation services in 2020 because of the pandemic. 

Polio immunisation activities were initially put on hold at the beginning of the pandemic in outbreak and endemic countries, although critical activities such as surveillance continued. The immunisation efforts resumed in those countries in July 2020. However, falling vaccination rates are also a major part of the problem in the US and other countries. During the pandemic, many children missed vaccinations when vaccine services were disrupted, noted the CDC in a report on the Rockland County polio case in New York. 

The WHO also points out that “polio workers have been at the frontline of pandemic response and immunisation recovery efforts”. 

“In many countries, particularly fragile and conflict-affected settings, the polio network provides critical support to the health system. Polio workers have decades of experience in identifying missed populations and using innovative strategies to reach them with healthcare. 

“Maintaining these networks is important to strengthen public health (and) advance primary healthcare towards universal health coverage and to strengthen global health security.”