A national emergency has been declared in the UK after health authorities detected evidence of a suspected polio outbreak in London.
The UK Healthy Security Agency (UKHSA) raised the alarm yesterday (22 June) after traces of the virus – extinct in the UK until now – were detected in routine sewage inspections in London between February and June.
While between one and three cases of polio are detected each year in UK sewage, UKHSA says these have all been isolated cases, unrelated to each other.
The most recent samples are genetically related, sparking fears the virus is being transmitted in the North East London communities served by the London Beckton Sewage Treatment Works, where the samples were found.
Despite efforts to eradicate the virus through vaccination, polio remains endemic in two nations worldwide, putting other countries at risk of importing cases.
UK parents have now been urged to ensure their children are fully vaccinated against the potentially deadly and paralysing disease.
NationalWorld has crunched the figures to find out which countries are home to polio, where has experienced recent outbreaks, and how many children remain unvaccinated in the UK and around the world.
How common is polio - and are cases increasing?
Polio (otherwise known as poliomyelitis, or paralytic polio) is caused by the poliovirus. Most people infected with poliovirus will have no symptoms, but some will develop poliomyelitis which can cause muscle weakening, paralysis, and sometimes death.
WHO launched a concerted plan in 1988 to eradicate polio by the year 2000.
It is thought the number of reported cases of paralytic polio is an underestimate, as people with acute flaccid paralysis – inflammation of the spinal cord leading to arm and leg weakness, which can be caused by polio – may not be detected or tested for the virus.
For this reason Our World in Data publishes both the number of reported cases and estimates of the true number, including those undetected.
Between 1980 and 2021, the number of reported paralytic polio cases fell from 52,630 to just 649 globally, while the number of estimated cases fell from 368,410 to 1,872 in 2020.
The below chart shows the decline worldwide since 1980. Can’t see the chart? Click here to open it in a new window.
There has been an upsurge in more recent years, however.
In 2016 there were just 42 reported cases – 49 once estimates of undetected cases are included.
But the following year both figures almost tripled, to 118 and 131 respectively.
Cases reached a peak of 1,253 reported and 1,872 estimated in 2020. The number of reported cases did fall back to 649 in 2021, although there is not yet an estimate of the true number that year.
Which countries have the most cases?
Nigeria was the polio hotspot in 2021, with 415 reported cases – 64% of the global total, and an increase from just eight the previous year.
That was followed by Afghanistan with 47 cases and Tajikistan with 32.
Afghanistan had the most confirmed cases in 2020, with 364, followed by Pakistan on 219 and Chad on 101.
These three nations also had the highest number of cases once estimates of undetected infections are included, with 404 in Afghanistan, 243 in Pakistan and 202 in Chad.
Historically, India has been the worst affected nation since 1980 with 293,708 confirmed and 1.96 million estimated cases – more than half the global total.
While polio remains rare in Europe, there was a significant uptick last year with 34 confirmed cases. The previous year there had been just one case, with zero cases for four consecutive years before that.
Ukraine had the highest number of cases in the continent, but still only confirmed two infections.
Polio is only endemic – consistently present and transmitted – in Afghanistan and Pakistan, according to the Global Polio Eradication Initiative, which warns that all countries remain at risk of importing cases until transmission is stopped in these nations.
In recent months, Malawi and Mozambique have both declared outbreaks of wild poliovirus, the most common type of polio.
How common was polio in the UK – and when was it eradicated?
According to Our World in Data the last confirmed case of polio in the UK was in 1993 – one case was reported that year, while the estimated true number stood at seven.
But the last case of UK polio actually transmitted within the UK came in 1984, according to Health Protection Scotland, with all cases between then and 1993 acquired outside of the UK and imported back.
The UK was declared to be officially polio free in 2003.
Are children in the UK vaccinated?
Analysis of the latest childhood vaccination coverage statistics published by the NHS shows wide geographical variation in the proportion of children vaccinated against polio.
The vaccine comes in a ‘six in one’ dose which offers protection against polio as well as other diseases such as hepatitis B and tetanus.
A primary course is given over the first few months of a child’s life with boosters required three years after completion of the primary course.
The UK vaccination rate during the 2020/21 period was at 92.6% – 2.4 percentage points lower than the World Health Organisation target of 95% to ensure herd immunity.
That is the proportion of infants vaccinated by their first birthday.
London has the lowest vaccination rate of any UK nation or region having vaccinated 86.7% of children before their first birthday during the 2020-21 period. The North West was the second worst performing region with 91.7% vaccinated. The North East is the only English region to be above the WHO target, having vaccinated 95.5% of children.
The vaccination rate across England is at 92.0%.
Northern Ireland was also below target with 94.5% of children vaccinated before their first birthday.
Scotland and Wales were the only two nations to achieve the goal with vaccination rates hitting 96.5% and 95.6% respectively.
How many children have been vaccinated across the world?
Polio mainly affects children under five, so early vaccination is vital to prevent transmission.
In 2020, 83% of infants around the world received three doses of polio vaccine, according to the World Health Organisation.
The map below shows vaccine coverage among one year olds around the world. Can’t see the map? Click here to open it in a new window.
But vaccine coverage can vary greatly by country. Only around two in five countries (41%) had vaccine uptake rates of 95% or higher in 2019, figures compiled by Our World in Data show. More than a quarter (31%) had uptake rates below 85%.
Papua New Guinea had the lowest coverage, with just 42% of one-year-olds immunised against polio. Twenty-seven countries had immunised 99% of one-year-olds, including China, Iran and Turkey.