Polio Vaccination Causes More Infections than Wild Virus
In rare instances, the live virus in oral polio vaccines can mutate and become infectious, causing new outbreaks.
Nov 25, 2019
Nigeria,
Democratic Republic of Congo, Central African Republic, and Angola have
experienced nine new cases of polio caused by the live virus in oral polio
vaccines that has mutated into an infectious form, according to statistics released last week
(November 20) by the World Health Organization. That brings the global total of
these types of infections to 157 for the year, and it means that more children
are paralyzed as a result of such vaccine-derived infections than illnesses
caused by the wildtype virus, which has affected 107 people this year.
Other countries in
Africa and Asia have also reported such vaccine-derived infections, which have
the potential to spark new outbreaks. In Africa alone, there are currently a
dozen vaccine-derived polio outbreaks, and another was declared in the
Philippines last month—the country’s first cases of the disease in more than 25
years, NPR reports.
See “Driven to Extinction”
To finally
eliminate the world of polio, global leaders convened last week (November 19)
at the Reaching the Last Mile (RLM) Forum in Abu Dhabi, pledging $2.6 billion to the effort.
The main impediment is vaccination coverage in certain regions, particularly
Afghanistan and Pakistan, the last two countries where polio remains to be eradicated.
While Western
countries use an injectable solution of inactivated virus, an oral polio
vaccine containing the live, attenuated virus is used for vaccination campaigns
in Africa and Asia because it is relatively cheap to produce and easy to
administer, requiring just two drops of medicine in the mouth. However, the
risk is that the attenuated live virus—in particular, type 2, which is at the
root of all current vaccine-derived polio cases, the Associated
Press reports—can mutate and become pathogenic. Fortunately,
vaccination can protect against such vaccine-derived strains. “The solution is
the same for all polio outbreaks: immunize every child several times with the
oral vaccine to stop polio transmission, regardless of the origin of the
virus,” the WHO
states.
“It’s actually
crazy because we’re vaccinating now against the vaccine in most parts of the
world,” Vincent Racaniello, a virologist at Columbia University, tells NPR,
“not against wild polio, which is confined to Pakistan and Afghanistan.”
Starting in April
2016, public health care workers around the world have made the transition from a trivalent
vaccine with types 1, 2, and 3 to a bivalent version without type 2 to prevent
such vaccine-derived cases.
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