Progress In
Achieving Worldwide Polio Eradication Is Reversed
Risk Of
International Spread Is Now At Highest Point Since 2014
“Gravely concerned”.
That’s how the International Health Regulations (IHR) Emergency
Committee meeting at the World Health Organization last month reacted
to the latest update on the progress of the international polio
eradication program.
The group noted the
significant increase in wild polio virus type 1 cases to 113 globally
as of December 11, 2019 compared to 28 for the same period in 2018. In
fact, the total number of wild polio cases in 2019 rose to 163 by
December 31, according to the Global Polio Eradication Initiative (GPEI).
Recommendation
Because it saw no
significant success yet in reversing the trend, IHR recommended that
countries with the potential to cause international spread should
conduct intensified activities. The three countries where polio wild
virus type 1 remains endemic are Pakistan, Afghanistan and Nigeria.
This latter country has not had wild polio cases in three years but is
still technically considered endemic. Pakistan and Afghanistan are
often referred to as an epidemiological block because of the polio
activity in the border area.
More Complications
If the increase in
wild polio cases was not enough, further alarm was caused by multiple
outbreaks of circulating vaccine derived poliovirus strains in
the four WHO regions of Africa, the Eastern Mediterranean, South-east
Asia, and the Western Pacific. The cause of the alarm is the rapid
emergence of vaccine derived polio virus type 2 strains in several
countries and this is “unprecedented and very concerning and not yet
fully understood”, according to IHR. Roland Sutter, former head
of polio research at World Health Organization, told Science News
“We are clearly in the most serious situation we have
been in with the program.”
Background on
Viruses
Three wild polio virus
strains (types 1, 2, and 3) are recognized, and types 2 and 3 were
certified as eradicated in 2015 and 2019 respectively. This was
achieved through the broad use of live attenuated oral polio vaccine (OPV)
containing vaccine virus against all three types (trivalent vaccine
OPV).
However, these vaccine viruses have the
capacity to
circulate and mutate causing paralytic polio in some children. The
GPEI reported 259 such cases of circulating vaccine derived
polio virus in 2019. Thus, while
the number of wild polio cases has declined 99.99% since 1988
according to the Centers for Disease Control and Prevention, the
existence of these vaccine derived polio cases is an unavoidable but
negative consequence of using live vaccine.
Type 2 Challenges
To prevent vaccine
derived polio, the use of the trivalent vaccine was halted in 2016
after the eradication of type 2 and bivalent vaccine with only type 1
and type 3 vaccine viruses was used. A monovalent type 2 vaccine was
created to help control outbreaks of vaccine derived type 2. However,
the number of vaccine derived outbreaks has been larger than expected
and it is unclear how frequently and how widely these type 2 vaccine
derived strains will circulate.
There is added concern
on the part of public health authorities since use of type 2 live
vaccine was halted after the eradication of the live virus and
millions of children are not protected against this vaccine derived
virus.
Some of the actions
recommended by the IHR to combat the current situation are:
1. Officially declare
poliovirus transmission as a national public health emergency and
implement or maintain all required measures to support polio
eradication.
2. Ensure that all
residents or longtime visitors get vaccinated against polio.
3. Intensify
crossborder efforts by significantly improving coordination at all
levels to substantially increase vaccination coverage of travelers
crossing the border and of populations that live near the border.
4. Intensify efforts
to increase routine immunization coverage.
Misinformation
The IHR urged all
countries, particularly those in Africa, to remain on high alert for
the possible importation of vaccine derived polio virus type 2 and to
respond to these importations as a national public health emergency.
IHR noted that resistance to vaccination among certain populations is
a significant factor in the spread of outbreaks, particularly in
Pakistan and Angola. It urged renewed efforts to combat myths and
misinformation about vaccines. This need is recognized in the US as
well as shown by the creation of a new Center for an Informed Public
(see related story in this issue.)
■
|