Poliovirus detected in wastewater in the Tampere region – no cases have been diagnosed, polio vaccination coverage is very good in Finland
Mutated vaccine-derived type 2 poliovirus has been found in wastewater monitoring conducted by THL. The virus was found in a wastewater sample collected in the Tampere region in November. Similar findings have been made in other European countries during the autumn. So far, no cases have been identified. In Finland, vaccination coverage against polio is very good.
Poliovirus has been found in wastewater monitoring conducted by the Finnish Institute for Health and Welfare (THL) in the Tampere region. The finding was determined to be mutated vaccine-derived poliovirus type 2 (VDPV2). VDPV2 is genetically derived from the original attenuated live virus strain contained in the oral polio vaccine.
The detection of the mutated type 2 poliovirus means that when the samples were collected, there were one or more persons who excreted poliovirus in the area. If a person who is completely or partially unvaccinated comes across said polio virus, they may be infected and, in rare cases, develop symptomatic polio.
“The finding is a rare one, but not entirely unexpected. A similar finding of mutated poliovirus was made in a wastewater sample in Finland about 10 years ago. The risk of a polio epidemic in Finland is low. We have one of the best polio monitoring systems in Europe, and vaccination coverage against polio is also high,” says Leif Lakoma, Chief Physician at THL.
Polio is monitored by means of wastewater testing in several European countries. This autumn, mutated type 2 polioviruses have also been found in wastewater monitoring in Spain, Poland and Germany. Testing conducted by the World Health Organisation (WHO) showed that the viruses are genetically linked to the virus strain originally detected in Nigeria, which is still circulating in several African countries. However, no cases of polio have been identified in Europe.
Vaccines containing live poliovirus are not used in Finland
Polio vaccinations began in Finland in 1957, and Finns are well protected against polio. The last polio case was diagnosed in Finland in 1985. In the same year, live oral polio booster vaccines were offered to the entire population.
Today, Finland uses injectable polio vaccines that do not contain live viruses, which means that the vaccine cannot cause polio. The vaccine is given free of charge as part of the national vaccine programme.
In children, vaccination coverage against polio is over 98%. The vaccine is administered at ages 3, 5, and 12 months old, and the protection is enhanced by a booster vaccination at 4 years of age. Adults must make sure that they have received a total of three doses of polio vaccine in their lifetime.
“We encourage everyone to make sure that their friends and relatives are duly vaccinated and to get any missing vaccinations, if necessary. This is particularly important for adults who have come to work or study in Finland from abroad and who may not be fully protected by the vaccines they should have received when they were children,” says Hanna Nohynek, Chief Physician at THL.
In addition, a booster vaccine is recommended for those travelling abroad if they intend to stay in a country with an increased risk of polio for more than four weeks and it has been more than 12 months since their last polio booster.
It takes effort to eradicate polio globally
The WHO has classified polio as an international public health threat since 2014. In Finland, polio is classified as a generally hazardous communicable disease.
It is easily transmitted through the gastrointestinal tract, either through contact, contaminated surfaces or food, and, less frequently, through respiratory droplets. In a small number of infected people, the virus can spread from the intestines to the central nervous system, causing paralysis and subsequent atrophy of voluntarily controlled muscles.
Endemic polio was eradicated in Europe more than 20 years ago. However, individual strains originating from the live polio vaccine are found in wastewater monitoring in Finland every year. These unmutated strains derived directly from vaccines do not pose a significant risk of further infection. Individual polio cases caused by the mutated vaccine-derived virus have been detected for instance in Ukraine in 2021 and in Israel in 2023.
The injectable polio vaccine provides effective protection against central nervous system damage caused by polio and its sequelae. However, an oral polio vaccine containing live viruses is still used around the world. For many years now, more polio cases have been caused globally by the mutated type 2 polioviruses derived from the live polio vaccine than what is known as the wild poliovirus.
According to WHO/Europe, poliovirus detections in Europe once again underscore the importance and urgency of eradicating all forms of the poliovirus.
The WHO is currently working on a new plan for the eradication of polio. The objective is to discontinue the use of the live polio vaccine, even though it provides better mucous membrane protection against polio than the injectable vaccine that does not contain live viruses.
Additional information
Leif Lakoma (polio)
Chief Physician
THL
Tel. +358 29 524 7898
[email protected]
Hanna Nohynek (polio vaccines)
Chief Physician
THL
Tel. +358 29 524 8246
[email protected]
Soile Blomqvist (polio monitoring)
Senior Researcher
THL
Tel. +358 29 524 8490
[email protected]
