The only effective protection against poliomyelitis, or polio for short, is vaccination. It is also the only way to eradicate the virus. But it's not that simple. "The original goal was to eradicate poliomyelitis by the year 2000," says Sabine Diedrich of the Robert Koch Institute (RKI) in Berlin. "Then it shifted further and further away." 

Next, there was a five-year plan. The plan ran from 2013 to 2018, and according to the virologist, "During this period we were supposed to manage finally to eradicate polio." But, Diedrich says, even that is still a very last, small step in the future.

Read more: Polio - a disease that haunts victims even later in life 

A Sisyphean task 

The World Health Organization (WHO) started its program exactly 30 years ago and has achieved a great deal. There are currently just three countries where poliomyelitis could not be eradicated: Afghanistan, Pakistan and Nigeria. 

The last of these, Nigeria, had not had any polio cases for a long time and the country had already been declared polio-free by 2015. But a year later, four cases broke out.

Four cases of polio — that doesn't sound like much in a country with 175 million inhabitants and an area the size of Germany and France combined. But every single polio sufferer represents a danger. So Nigeria is back on the list of endemic countries. It is still there.

The invisible danger

The fatal thing about poliovirus is that the disease can be invisible at first and therefore spreads rapidly. "The danger that polio will return to Germany is still there," warns Diedrich. "Because viruses unfortunately know no borders. Globalization, people's desire to travel, but also migratory movements increase the risk that the virus and thus the disease could be brought back to Germany.

An endless cycle

Compared to polio, even the eradication of smallpox was relatively easy because every infected person also fell ill. These people could be isolated and so it was much easier to manage than polio. Those infected with polio, in contrast, are often difficult to spot.

Only one person in every 200 infected with polio falls ill. "So, if I see a single person who has polio, I can assume that there are at least another 200 people who have no symptoms, but are carrying the virus and could pass it on," Diedrich says.

The oral polio vaccine is used in many countries. It contains attenuated live vaccine viruses that activate an immune response in the body. This live virus multiplies in the intestine. This has the advantage for the vaccinated person that, in contrast to a dead vaccine, a so-called intestinal immunity is formed.

But this also involves an element of risk: During this time, the patient excretes the vaccine virus. The excreted vaccine virus can spread in areas with insufficient immunity in the population.

Hygiene is a critical factor in controlling polio, as the most common way of transmitting the virus is via contaminated hands. The virus can be passed from person to person, as humans are the only carriers of polio. For the RKI scientist, consistent vaccination is the only promising measure.

Read more: Vaccination remains a challenge in Africa 

Symptoms

The first symptoms of the disease usually appear after a few days but are initially atypical. A mild flu-like infection occurs, almost like summer flu, also with a fever. Then comes a phase in which people feel relatively well.

But then comes a second phase. "That's why polio is called biphasic," explains Diedrich. The first paralysis can occur after 10 to 20 days. So-called acute, flaccid paralysis of the extremities occurs, for example, in the legs and arms. In rare cases, the respiratory muscles can also be affected. Then the patient requires artificial respiration. For a long time now, the iron lung has no longer been in use, as it was in the 1950s. This was the first clinical device of its kind at that time.

Many patients had to spend their entire lives in this prison made of steel.

Good, but not yet good enough

The vaccination campaigns have been very successful. Since 2000, more than 10 billion doses of vaccine have been administered to nearly 3 billion children around the world. Vaccination rates have increased worldwide. At the same time, the number of polio cases has decreased. Thirty years ago, there were about 350,000 cases per year worldwide. One thousand children contracted polio every day.

In recent years, the figure has been well below 100 per year. Last year, 22 cases of polio were registered; this year there are still 20 worldwide. 

"We, here at the Robert Koch Institute, are still very optimistic that polio can be eradicated in the next few years. But as long as there is only one case left somewhere, it can quickly become more," Diedrich explains. The top priority is to vaccinate, vaccinate, vaccinate!
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