In 1988, the world committed to eradicating wild polio. Today, 5 out of 6 WHO regions are certified free of wild polio, including the WHO European Region, which was declared polio free in 2002. Only 2 remaining countries in the world have endemic circulation of wild poliovirus. In addition, 2 of the 3 types of wild poliovirus have been eradicated.
But amid this incredible progress, challenges to reach every child have persisted in all regions and been further exacerbated by the COVID-19 pandemic. Many countries in the European Region and around the world have reported dips in routine immunization coverage as health care and immunization systems have been stretched to accommodate surges in COVID-19 infections and vaccination rollout. Any decrease or gap in routine coverage creates opportunities for vaccine-preventable diseases, including polio, to spread among the unvaccinated.
On World Polio Day (24 October), WHO and the Global Polio Eradication Initiative, an alliance of key partners and stakeholders, call on countries and parents to stay vigilant in the fight against this disease. As the COVID-19 pandemic clearly demonstrates, diseases do not stop at borders, and as long as polio exists somewhere in the world, we have to continue vaccinating everywhere.
Holding the line
To sustain the European Region’s polio-free status, it is vital to vaccinate all children according to national routine immunization schedules and to quickly detect any importation or possible emergence of a vaccine-derived strain of the virus. If a case is detected, immediate action must be taken to prevent further transmission.
Acute flaccid paralysis (AFP) is a symptom that indicates the possible presence of poliovirus, yet it can also have other causes. Surveillance systems must be strong enough to pick up on every case of AFP and ensure it is tested for polio in order to be 100% sure that it is caused by something other than polio, and that polio is not present in the country.
Developments in the European Region
Several importations of polioviruses into the European Region have been detected since the Region was declared polio free in 2002. Each event was detected thanks to functional national polio surveillance together with a strong network of polio surveillance laboratories in the Region, and the ensuing outbreaks were stopped. The 2010 importation of wild virus into Tajikistan and eventual spread into 3 other countries was the largest outbreak to date in the Region since 2002.
Currently, 2 countries in the Region are responding to vaccine-derived poliovirus outbreaks. In Tajikistan, an initial case was confirmed in January 2021, and 3 rounds of supplemental immunization campaigns have been conducted to stop its spread. In Ukraine, 1 case of polio was confirmed on 6 October 2021, and the first of several immunization campaigns has been initiated.
These events underline the fragility of the Region’s polio-free status and the ongoing importance of ensuring that every child is protected through immunization – including those who live in countries that have not seen cases of polio for decades.
What is vaccine-derived poliovirus?
Although it is rare, cases of polio can occur in polio-free regions, either through importation of a wild or vaccine-derived strain, or through emergence of a vaccine-derived strain in areas where a high proportion of people are unvaccinated. In the latter situation, a weakened strain of the poliovirus that was used in oral polio vaccine can continue to spread widely among unvaccinated people for a long time, which can eventually lead to genetic mutations that cause the virus to behave more like the “wild” virus that causes paralytic polio.
A fully immunized population is protected against both vaccine-derived and wild polioviruses.