Polio: why polio cases are increasing

Fear of polio has long been low. Viruses have now been detected in the US and UK. Is polio coming back? How dangerous is an infection? What role do vaccinations play?

Just a few decades ago, polio was one of the most feared diseases. However, a worldwide vaccination campaign was able to largely contain the viral disease with the medical name poliomyelitis, or polio for short. Vaccination against the polio virus has been widespread in Germany since the 1960s. Since then, the number of cases has fallen sharply. The last known case dates back to 2000.

But now reports are increasing worldwide that polioviruses have been detected in wastewater, including in the US state of New York and in Great Britain. Experts are alarmed, apparently the virus is circulating in the population. The state of New York declared a disaster. What are the reasons for the increase in polio cases? Answers to important questions at a glance:

Poliomyelitis? Wasn’t that eradicated?

The final eradication of the polio virus is the declared goal of the World Health Organization (WHO), but it has not yet been achieved. Instead, the situation is serious: In 2014, the WHO identified a “health emergency of international concern” for polio, which still applies today. The original wild type of the virus is not the biggest problem: Almost all countries in the world are currently considered wild polio-free, only in Pakistan and Afghanistan is the virus still considered native.

So-called vaccine viruses cause significantly more cases. These are derived from the weakened viruses used in the major vaccination campaigns to immunize people. The viruses used are modified in such a way that in most cases they do not trigger any symptoms, but do trigger an immune response against the virus.

However, these weakened viruses are excreted by the vaccinated in the stool and can be transmitted to other people through smear infections, i.e. touching, especially in environments with low hygienic standards. As long as these are attenuated vaccine viruses, this is usually harmless. But the virus can change again: the longer the virus circulates in population groups without immune protection, the greater the danger.

“Some of these vaccine viruses have made changes so that they can cause illness in the same way as was originally the case,” explains Reinhold Förster, Professor of Immunology at the Hannover Medical School. “This puts you at risk, but it’s only relevant for people who aren’t vaccinated.”

In order to prevent infection with former vaccine viruses, a vaccine containing inactivated polio viruses, a so-called dead vaccine, has been used in Germany since 1998.

Why and where are cases now increasing again?

According to the WHO, there have been cases of paralysis caused by polioviruses worldwide in recent years, which originate from a live vaccine. In 2020 there were 1113, last year 688. The majority of these were registered in Afghanistan and Pakistan, but also in African countries such as Nigeria and Chad. So far this year, 120 cases of paralysis in Yemen alone have been recorded.

But experts are also alarmed in western countries: in the USA, polio viruses were detected in a patient. Sewage studies showed that the virus has been circulating in the region for some time. The viruses were also detected in sewage samples in London and there was a polio outbreak in Israel in March 2022, in which an unvaccinated child developed paralysis. Six others were infected but showed no symptoms.

Experts see the reason for these outbreaks as the vaccination rates being too low: “We can eliminate the virus if 95 percent of the population is immunized,” says immunologist Förster. “If we go well below that, we have a problem.”

The American and British authorities therefore called on their population to have themselves and their children vaccinated in response to the polio virus finds in the sewage.

How does poliovirus infection show up?

“Currently it is very, very unlikely to come across polio in Germany,” explains Jakob Maske, spokesman for the professional association of paediatricians. “And maybe we wouldn’t recognize them at all.” Because in most cases an infection with polioviruses is quite harmless: cold symptoms such as headaches or gastrointestinal problems are a normal course.

However, according to the Robert Koch Institute, around four to five percent of those affected develop meningitis. Paralysis, the most severe form of polio, occurs in 0.1 to 1 percent. “This can be severe paralysis of the extremities or respiratory paralysis. This can lead to death,” explains pediatrician Maske. The signs of paralysis, for example on the feet or hands, do recede, but usually only partially. The consequences of the disease last a lifetime.

There is no therapy that works specifically against polio. “When you develop severe polio that becomes debilitating, you can’t mitigate it. And even if you’re not severely affected at first, polio can still cause severe symptoms years later.” However, the name polio is misleading: “Ultimately, the disease is equally dangerous for all age groups,” says Maske. “Therefore, vaccination is extremely important for everyone.”

Are additional vaccinations necessary?

In Germany, infants are already vaccinated against polio as standard. The Standing Vaccination Commission (STIKO) recommends a total of three vaccination doses in the first year of life, premature babies receive another vaccination. A refresher course should be given as a school child, usually between the ages of ten and twelve.

After that, long-term protection should have been built up; according to STIKO, no further refresher is normally necessary. However, before traveling to affected areas, it may be advisable to have another vaccination. “If you comply with the regular vaccinations, the children have very, very good protection and it is not to be expected that they will contract polio,” says Maske from the professional association of paediatricians. Further vaccinations are not necessary in the current situation.

However, according to the Robert Koch Institute, the vaccination rate for children born between 2008 and 2018 is quite constant at only 90 percent, and in some older population groups it is significantly lower.

Paediatricians regularly discuss the question of whether vaccination against polio is necessary with parents, according to pediatrician Maske. “Some parents think they don’t need the polio vaccine because we don’t have the disease anymore. But that’s a fallacy.” If you reduce the vaccination quota, it could happen very quickly that such a virus would spread again – at least among the unvaccinated.

Immunologist Förster also warns against underestimating the danger of polio infection: Many children were seriously ill in the 1950s and 1960s, they had to be ventilated and some died. “It’s really frightening to see how carelessly this danger is accepted again.”