It is difficult to imagine in the Western world how much of a scare poliomyelitis was as recently as a few decades ago. Literary sources, such as the novel "Nemesis" by American author Philip Roth, which has a PolioEpidemic in the 1940s in its plot, give us an impression of what it was like when there was neither therapy nor prevention available for this disease. The term, "infant paralysis", commonly used as a synonym for poliomyelitis, was not quite accurate: The disease triggered the much-feared crippling only in a fraction of the patients, and children, although afflicted most often, were not the only victims.
US President Franklin D Roosevelt was probably one of the most prominent adult victims of Polio – although medical historians are now discussing the possibility that Roosevelt's paralysis may have had different causes. During his time in office, he was very active for charity organisations seeking to fight Polio. As late as in the 1950s, Polio "was an ever-present topic in the USA, almost as much as the atomic bomb," says Prof Ulrike Lindner, who is a historian at the University of Cologne. "Many motion pictures were preceded by trailers advertising the fight of the National Foundation against Polio."
The pathogen, i.e. poliovirus, is a member of the enteroviruses that can proliferate in the human intestines and includes three different types - type 2 is considered to be eradicated, whereas type 1 and 3 still circulate in endemic areas. If hygienic conditions are poor, Viruses are transmitted through contact with body fluids, specifically by contact with faeces. In most cases (approximately 90%), the Infection proceeds unnoticed or with mild symptoms only. Frequently, the disease does not progress beyond fever, often associated by diarrhoea and vomiting. But in a fraction of the infected individuals, the nervous system is afflicted too. This course of disease can lead to meningitis and the much-feared and persistent paralysis and deformation.
In 1955, Jonas Salk successfully completed the development of the first vaccine, a so-called "dead-vaccine" made up of killed pathogens, that was administered by injection. The application of this IPV (inactivated polio vaccine) reduced the number of new cases of the disease in the USA significantly. The live-Vaccine OPV (oral polio vaccine), which was developed soon thereafter and can be administered by oral intake, then was the breakthrough in most European countries. In Germany, OPV was used on a large scale starting in 1960 (German Democratic Republic) and 1962 (Federal Republic of Germany) leading to the disappearance of Polio soon thereafter.
Both vaccines have their advantages and disadvantages
says Prof Carlos Guzmán, who directs the "Vaccine Research" department at the HZI.
"The IPV vaccination, which has become the standard in Europe, reliably protects the vaccinated individuals from disease, i.e. from paralysis," according to the vaccination recommendations issued by the Robert-Koch-Institute. "But persons vaccinated with IPV can still get infected by PolioViruses and might excrete and spread them.“
In contrast, OPV contains live, attenuated Viruses and immunises the intestinal tract more effectively. However, there is always a minor risk that the Viruses might mutate and become more dangerous again. In Germany, where Polio has been eradicated, the Live vaccine OPV is not used any longer for this reason.
The World Health Organization WHO recommends the use of a combination of OPV and IPV only for countries, such as Pakistan and Nigeria, in which the virus is still rampant.
Owing to successful vaccination campaigns, the number of global cases of the disease has dropped by 99%, from 350,000 in 1988 to approximately 400 in 2013.
It used to be common belief that vaccinations against Polio work so well because the pathogens basically remain unchanged - unlike, for example, influenza Viruses, which cause the seasonal Influenza. A pathogen displaying unchanged surface structures makes it easy for the immune system to store this information in a "molecular memory".
But researchers made a disconcerting discovery in 2010: In the Congo, they discovered a mutated form of the pathogen against which the common protective vaccine is ineffective. "This was the first evidence indicating that Polio-Viruses may also be able to "drift", i.e. to generate new genetic variants," explains Prof Christian Drosten, who is a virologist at the University of Bonn, whose team participated in the discovery.
Experts think that the possibility of a return of the "classical" types of Polio might be even more dangerous than the potential spreading of drift variants: "We are seeing a resurgence of Polio in conflict regions, such as Syria," says Christian Drosten. Carlos Guzmán explains, "a boycott of vaccination programmes in Nigeria several years ago has caused the number of cases to be on the rise again."
Because of new outbreaks in three countries early in 2014 – Afghanistan, Iraq and Equatorial Guinea – Margaret Chan, Director-General of the WHO in May proclaimed the spreading of Polio to be a Public Health Emergency of International Concern. The World Health Organization expressly recommended epidemic control measures for ten countries: Equatorial Guinea, Cameroon, Pakistan, Syria, Afghanistan, Ethiopia, Iraq, Israel, Nigeria and Somalia.
But Central Europe should not feel too safe either, explains Christian Drosten: "The level of vaccination against Polio in Germany is fairly poor by now, not least because vaccinations are not being boosted. In addition, there is little basic research ongoing in this field. An introduction of Viruses would be a major problem for us." Drosten warns against taking this risk lightly: "The whole worlds talks about Ebola - for good reason. But an outbreak in Central Europe would be much more realistic in the case of Polio, I think.“