Download Polio in the Holy Land by Dr. David L. (“Woody”) Woodland (as

Polio in the Holy Land
by Dr. David L. (“Woody”) Woodland
(as published in the Summit Daily News of February 6, 2014)
Several months ago, I wrote a (Petri) Dish article about the polio vaccine and efforts to eradicate
the disease from the globe. I focused on the two types of vaccines: a live but weakened form of
the virus developed by Albert Sabin and a killed form of the virus developed by Jonas Salk, both
of which have been used to control polio. The live, orally delivered vaccine is the foundation of
the eradication effort since it is easy to deliver, induces strong immunity in the gut, and prevents
virus transmission. While this live virus vaccine is the primary tool for polio eradication, on rare
occasions it can revert to a virulent form, causing paralysis and other severe side effects. The
killed vaccine is much less potent and less effective, but is far safer since it is not associated
with severe side effects. The strategy for polio eradication has been to use the live vaccine as
the primary approach to controlling polio in an endemic area and then switch to the killed
vaccine to prevent polio reoccurrence.
This strategy has worked well, and polio is close to being the third infectious disease eliminated
from the globe. But the recent reappearance of the polio virus in Israel has caused health
officials to reconsider this strategy. Polio was essentially eradicated in Israel following the last
major outbreak in 1988. To maintain this polio-free status, Israeli health authorities switched
from the live to the inactivated polio vaccine in 1995, and vaccination rates with the killed
vaccine are now as high as 95% of the population. However, routine sewage monitoring late last
year revealed the presence of wild polio virus across the country and in the West Bank and
Gaza, indicating widespread transmission. No actual cases of paralytic disease have been
identified, presumably due to the high vaccination rates. But the presence of the virus in sewage
raises the alarming specter of transmission to other countries, especially given the prolonged
circulation over a large area.
How could this happen in a country with such a comprehensive vaccination campaign? A clue
comes from the fact that there have not been any clinical cases of polio, despite widespread
distribution of the virus. This suggests that there are individuals who are actively shedding the
virus without succumbing to the disease. Indeed, Israeli medical authorities have now identified
many individuals who were shedding poliovirus in their feces, despite having been fully
vaccinated with the killed polio virus vaccine. It is becoming apparent that the re-emergence of
the virus results from the lower efficacy of this killed vaccine. Although both the live and killed
vaccines stop virus from entering the nervous system and thereby prevent the development of
the polio disease, only the oral live vaccine is able to generate strong enough immunity to
eliminate the virus from the gut. In other words, some individuals who received the killed
vaccine and who are subsequently exposed to the polio virus can possess the ability to harbor
the virus in their intestines. These “carriers” are actively excreting live virus, thereby explaining
the appearance of virus in the Israeli sewage system. This highlights a potential weakness in
the polio vaccine strategy; the exclusive use of the inactivated virus vaccine can actually hide
transmission of the virus since it potentially facilitates development of asymptomatic carriers of
the disease.
The experience of Israeli medical authorities demonstrates that polio continues to be a global
threat. While the situation in Israel can be controlled by reimplementation of the live attenuated
vaccine, considerable challenges remain in countries where vaccination rates are low. For
example, polio has re-appeared in Syria where the disease had been considered eradicated for
over a decade. Obviously, the civil war in that country poses considerable difficulties for the
polio vaccination campaign, raising fears that there will be a widespread epidemic in the region.
Sustained and relentless efforts by the global polio eradication initiative will be essential to keep
a lid on this dreadful disease. An important step was Secretary of State John Kerry’s
announcement on January 15 that the US will provide $380 million in additional humanitarian
assistance to those affected by the war in Syria. Some of this funding is for childhood
vaccination campaigns in the region. Let’s all hope that it’s successful.
David L. “Woody” Woodland, Ph.D. is the Chief Scientific Officer of Silverthorne-based Keystone
Symposia on Molecular and Cellular Biology, a nonprofit dedicated to accelerating life science discovery
by convening internationally renowned research conferences in Summit County and worldwide. Woody
can be reached at 970-262-1230 ext. 131 or [email protected].
For more (Petri) Dish columns, visit www.keystonesymposia.org.