Polio: only a plane flight away

The World Health Organization last week declared the spread of polio to be an international public health emergency, describing it as an 'extraordinary event' which called for ‘a co-ordinated international response’. This is only the second time in the WHO’s 65-year history that it has made such a declaration, which reflects the seriousness of the situation.

On paper, the numbers look relatively small – 68 cases of polio confirmed worldwide in the first four months of 2014, which is about three times the number for the same period in 2013. However, although the polio virus is endemic in just three countries – Pakistan, Afghanistan, and Nigeria – the number of countries affected by polio is growing. Attacks on vaccination campaigns and civil unrest have allowed the virus to spread across borders.

Syria, which was polio-free for 14 years, was re-infected with the virus from Pakistan. Polio cases there have increased as a result of the civil war, which has had a major impact on sanitation and on routine vaccination. An estimated 9 million refugees have fled from Syria into neighbouring countries. So far polio outbreaks have been checked by mass vaccination campaigns undertaken by countries like Jordan and Turkey, but there is a high risk of the virus spreading still further.

In Africa, the WHO is also extremely concerned about the situation in Cameroon, which borders on the areas of Nigeria that have shown most opposition to polio vaccination. As well as Syria and Cameroon, WHO lists Pakistan, Afghanistan, Equatorial Guinea, Ethiopia, Iraq, Israel, Somalia and Nigeria as ‘posing an ongoing risk for new wild poliovirus exportations in 2014’.

The WHO is recommending that citizens of affected countries travelling abroad carry a vaccination certificate. However, unless this is enforced, it is possible for infected people to slip through the net and introduce the virus into countries which are currently polio-free. Around 90% of polio infections cause no symptoms at all, so people may travel not knowing that they are carrying the disease.

The situation in Israel underlines the potential risks faced by developed countries. Wild poliovirus has been found in sewage in several towns in the south of Israel since February 2013. No actual clinical cases of polio have been confirmed, but as a precaution Israel began to administer the oral polio vaccine (more effective at stopping this kind of ‘silent transmission’ than the inactivated polio vaccine now routinely used in Europe and the USA) to nearly 900,000 children.

Israel routinely monitors sewage for poliovirus, but few other countries do, even in Europe. This has sparked concerns that the polio virus could be introduced by an infected traveller and spread undetected through a population. Ultimately, there is a risk of transmitting polio to people who are not protected by vaccination.

The last case of natural polio infection caught in the UK was thirty years ago. Although levels of polio vaccination are high in the UK, meaning that a full-scale outbreak is unlikely, the recent spread of polio does make it more likely that cases may occur again in the UK. This underlines the continued importance of vaccination against diseases like polio, even when the risk within the UK itself seems very low.

Read the full WHO statement .