VACCINE RESISTANT POLIO STRAIN DISCOVERED
The global initiative to eradicate poliomyelitis through routine vaccination
has helped reduce the number of cases by more than 99% in 30 years, from an
estimated 350,000 cases in 1988 to 650 reported cases in 2011. However, major
epidemics are still occurring today, such as the ones in the Republic of the
Congo in 2010, Tajikistan in 2010, and China in 2011. The epidemic outbreak in
2010 in the Republic of the Congo differed from the others in its exceptionally
high mortality rate of 47%: out of the 445 confirmed cases, nearly 210 died.
The researchers first attributed the seriousness of the epidemic to low vaccine
coverage.
Newly identified
mutations of the virus
In reality, the cause
was something completely different. An international team including IRD
researchers has just identified the virus responsible and sequenced its genetic
material. The genetic sequence shows two mutations, unknown until now, of the
proteins that form the "shell" (capsid) of the virus. On the face of
it, this evolution complicates the task for the antibodies produced by the
immune system of the vaccinated patient as they can no longer recognize the
viral strain.
The researchers then
tested the resistance of this variant of poliovirus on blood samples from more
than 60 vaccinated people, including volunteers living in neighbouring Gabon,
where part of the research team was based, and German medical students. Their
antibodies were shown to be less effective against the Congo strain than against
the other strains of poliovirus. The researchers estimate that 15%-30% of these
people would not have been protected during the 2010 epidemic.
At a time when the
global campaign to eradicate poliomyelitis is entering its final phase,
researchers fear that other variants of the virus may emerge among populations
immunised with the vaccine. Undoubtedly, these strains are circulating in
nature. While quite rare, they could lead to fatal epidemics such as the one in
2010 in the Republic of the Congo if they reach areas where the more common
strains have been eradicated, but where vaccine coverage is insufficient. The
researchers are calling for better clinical and environmental monitoring to
completely wipe out the scourge of polio.
Comments
Post a Comment