POLIO- MUTATED VIRUS BREACHES VACCINE PROTECTION
Thanks to effective
vaccination, polio is considered nearly eradicated. Each year only a few
hundred people are stricken worldwide. However, scientists of the University of
Bonn, together with colleagues from Gabon, are reporting alarming findings: a
mutated virus that was able to resist the vaccine protection to a considerable
extent was found in victims of an outbreak in the Congo in 2010. The pathogen
could also potentially have infected many people in Germany.
The polio epidemic in
the Congo in 2010 was especially serious. 445 people were verifiably infected,
mostly young adults. The disease was fatal for 209 of them. This high mortality
rate is surprising. Also important was the fact that many of those affected had
apparently been vaccinated: Surveys indicated that half of the patients
remembered having received the prescribed three vaccination dosages. To date
the vaccination has been considered a highly effective weapon for containing
the polioviruses that cause the disease.
"We isolated
polio-viruses from the deceased and examined the viruses more closely,"
explains Dr. Jan Felix Drexler, who is in the meantime working in the
Netherlands. He carried out the study during his employment at the Institute
for Virology of the University Hospital of Bonn under the supervision of Prof.
Christian Drosten, together with his colleagues from Gabon, Dr. Gilda Grard and
Dr. Eric Leroy. "The pathogen carries a mutation that changes its form at
a decisive point." The result: the antibodies induced by the vaccination
can hardly block the mutated virus and render it harmless.
The researchers have
examined the success with which the new pathogen evades the immune system. To
this purpose, they tested, among others, blood samples from 34 medical students
of the University of Bonn. All of them were vaccinated in childhood with the
usual methods against polio. And very successfully, as an initial test showed:
The antibodies in the blood of the test subjects had no problem combating
"normal" polio viruses. The situation was different with the mutated
virus; the immune reaction was much weaker here. "We estimate that one in
five of our Bonn test subjects could have been infected by the new polio virus,
perhaps even one in three," says Prof. Drosten.
Eradication possible
The World Health
Organization (WHO) has undertaken the goal of eradicating the polio virus in
coming years. The role model here is smallpox -- thanks to a consistent
vaccination strategy, the earth has been classified as free of smallpox since
1980. The chances are principally good that something similar could succeed
again: The polio virus can also only be transmitted from person to person.
There are thus no pathogen reservoirs in animals from which the disease could
spread repeatedly. Similar to with smallpox, the polio vaccines also offer
extraordinary protection. This, however, does not apply when the virus mutates.
"When such an altered pathogen encounters a population that has not been
consistently vaccinated enough, then things get dangerous," the scientists
warn.
The polio epidemic in
the Congo was stopped with a massive vaccination program and hygiene measures.
Even the current vaccines thus appear to be good enough to be effective when
they are promptly and consistently administered. The new pathogen is
nonetheless a warning: "We can't afford to sit back and do nothing,"
the scientists warn. "We need to further increase the vaccination rate and
develop new, more potent vaccines. Only in this way do we have a chance of
permanently vanquishing polio."
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