History and Management of Polio Eradication
Maureen Gallagher
Introduction
In 1980,
smallpox was finally declared to be eradicated globally—a great victory for the
world and for epidemiology. Seeing this
could be done, we then decided to take on polio. Polio had been, after all, under control in the U.S. at this time
with only sporadic vaccine-induced or imported cases. Rather, no wild-type disease had been seen for several
years. And, like smallpox, humans were
the polio virus’s only known reservoir, making a stop to transmission
theoretically plausible. Furthermore,
there were two viable and effective vaccines—one need only mobilize the world
together in an effort to reach all developing world children still being
infected, as they were not all being sufficiently immunized, to maintain an
appropriate herd immunity or to stop transmission altogether as in the United
States.
What is polio?
Poliomyelitis,
though not so identified until 1789 by Englishman Michael Underwood, has
probably been around since at least 1580 BC according to historic records
indicating a similar paralytic disease (www.endof polio.org). However, the first recorded outbreaks of
this so-named virus in Europe were in the early 19th century. Outbreaks were then reported in the U.S. a
few years later. Over the next century,
epidemics appeared each summer and fall in both the U.S. and Europe, each year
becoming more severe. Then in 1952,
shortly before the development of the first vaccine, there were a record number
of incident cases (over 21,000). Early
treatments included the “iron lung” for those with paralysis of respiratory
muscles—
from http://www.endofpolio.org/home.html
Poliomyelitis
is classified as an RNA enterovirus, residing in the gastrointestinal
tract. It has three serotypes (1, 2,
and 3) and is transmitted most often via the fecal-oral route, though oral-oral
transmission is also theoretically plausible.
One is most infectious from 7-10 days before and after symptoms appear but
the virus can still be detected in stool samples for 3 to 6 weeks afterwards (www.cdc.gov). The virus is also highly contagious, with
seroconversion rates of 90 to almost 100% among household members of infected
individuals (www.cdc.gov).
Polio
typically has an incubation period of 6 to 20 days but can range from 3 to 35
days. Its only known reservoir is
humans, and is usually passed along by someone who is infected but
asymptomatic. Surprisingly, these
asymptomatic and undetected cases account for approximately 95% of all polio
infections. Furthermore, it is
estimated that only one in 200 of all infected develop a paralytic form of the
disease.
Also,
another 4-8% might contract a minor, nonspecific illness (www.cdc.gov), indistinguishable from an upper
respiratory tract infection, fever, and/or nausea and vomiting. An even smaller subgroup are afflicted by a
non-paralytic aseptic meningitis which typically lasts about a week and then
the individual makes a full recovery.
For those suffering
from paralysis (less than 1% infected), one would experience initial paralysis
1 to 10 days after the non-specific viral symptoms aforementioned. Some patients actually recover use of
affected limbs but many do not. Usually
if paralysis continues for a year or more, full recovery will not be made as in
the former case.
There are three types of paralytic polio—spinal, bulbar, and
bulbospinal. The former is the most
common of the three, usually resulting in a form of leg paralysis. Bulbar polio, the least common, contributes
to loss in muscle function adjacent to cranial nerves. The bulbarspinal form represents approximately
19% of cases and is a combination of the former two types. Case-fatality rates for paralytic polio are
estimated to be 2-5% for children and 15-30%, but tend to increase among bulbar
paralysis cases (www.cdc.gov).
Search for a vaccine
Currently there are two effective
vaccines available—IPV (inactivated polio vaccine), developed by Dr. Jonas Salk
in 1954, and OPV (oral polio vaccine, based on a weakened live virus),
developed in 1957 by Dr. Albert Sabin.
The IPV vaccine was used exclusively in this country until
the early 1960’s when OPV replaced it as the preferred form of polio
immunization. Now, however, it has been
replaced by exclusive use of IPV.
Our own Frederick Robbins, MD, of Case
Western Reserve University helped pave the way for the development of these
monumental vaccines and shared the Nobel Prize in 1954 in physiology or
medicine for his significant contributions to our knowledge of polio
epidemiology. It was he, along with his
colleagues (John F. Enders, PhD, and Thomas H. Weller, MD), who were first able
to cultivate the polio virus in tissue culture. Polio previously was known to be a virus but had never before
been thus isolated; rather, work had only been done using monkey
specimens. Furthermore, it was only
through the achievement of this milestone that it became possible to develop
the subsequent vaccines.
After his work isolating the polio
virus, Dr. Robbins became very involved with the initial vaccine efficacy
trials for the Salk vaccine (IPV).
Needless to say, the vaccine was determined to demonstrate sufficient
efficacy and soon after became available to distribute to the public.
IPV is highly effective for
producing immunity to polio with 90% immunity after two doses and 99% after
3. However, the duration of the
immunity is not certain. OPV is also
highly effective in producing immunity with 50% immunity after the first dose
and 99% after the third. In addition it
is considered to provide lifelong immunity.
Furthermore, it was through its exclusive use until the 1980’s that the
U.S. was able to become polio-free (willd-type virus infection rather).
But now that the U.S. and other
countries have been declared polio free, the goal is now to eliminate any
vaccine-related infection. Thus, the
IPV vaccine has a decided advantage in that it does not contain the live virus
as does OPV and cannot cause vaccine-associated paralytic polio (VAPP). In 1996, a combined IPV/OPV regimen was
recommended. Then in July of 1999, the
exclusive use of IPV was recommended.
According to the CDC, VAPP occurs in
one out of every two to three million OPV doses administered. Since 1980, this then accounted for 95% of
all cases in the U.S. (approximately 8-10 cases per year with the remaining
infections imported from polio-endemic regions). But since the use of exclusive IPV, VAPP has been eliminated,
with the last case reported in 1999.
However, in developing countries,
OPV still remains the vaccine of choice--it is much easier to administer among
populations as it does not require an injection as well as being cheaper to
manufacture. Because of this, the
benefits far outweigh the risks of VAPP.
That is, it would be much greater threat to the community if all the
children were not vaccinated as the virus is still endemic.
A commitment toward eradication
As mentioned, the U.S. has been
officially declared polio free, witnessing its last wild-type infection in
1979. This particular infection was
found to have been imported from the Netherlands. Then in 1994 after mass immunization campaigns, the entire region
of the Americas was declared polio free.
In 2000 the Western Pacific followed suit. Finally, in June of 2002, the 51 countries of the “Euro” region
were declared free of polio as well (www.unicef.org). Overall, as of 2000, new world-wide cases
dropped to 2,979, then decreasing to 500 in 2001.
However, this progress could not
have been made without all of the extraordinary effort and collaboration that
has been a part of the eradication campaign.
So how have we come so far, one might wonder?
In 1988 the global eradication
initiative was officially launched by the world’s health ministers at the 41st
World Health Assembly with a goal of eliminating polio by the end of the
century. Furthermore, this resolution
specified that this was to be achieved through the Expanded Programme on
Immunization (EPI), and through the strengthening of primary health care
facilities and structure. Many partners
became committed to this goal, such as The World Health Organization (WHO),
Rotary International, The Center for Disease Control and Prevention (CDC), as
well as the United Nations Children’s Fund (UNICEF).
WHO and UNICEF together lead in the
coordination of the operation. WHO
works closely with individual country ministries of health, as well as the
training and deployment of health workers internationally. In addition, they have been instrumental in
establishing certification standard acute flaccid paralysis (AFP—important in
coordinating active surveillance activities), as well as the coordination of
resources and advocacy. Furthermore,
WHO will help determine when and if eradication finally has been achieved using
their developed criteria. In fact, Dr.
Robbins currently sits on the committee that oversees this process.
UNICEF, like WHO, works closely with
endemic country ministries of health, helping distribute vaccines while
maintaining the essential cold chain (procedure for maintaining the viability
of the live vaccine, transporting it from refrigerated site to site in a
standard cooler). In the mid 1990’s the
Vaccine Vial Monitor was added to individual vials to determine for sure if the
vaccine was still viable.
Rotary International, the largest
humanitarian organization worldwide, has provided a substantial amount of
funding in addition to a network of volunteers worldwide to assist in the
campaign via immunizations themselves as well as training and advocacy
programs. They were also instrumental
in bringing the polio eradication campaign to the foreground as an
international priority, paving the way for the official goal of worldwide polio
elimination by the year 2000 (which was changed to 2005 in the late 1990’s, though
much progress has been made).
The CDC has been instrumental in
providing state of the art lab support, identifying particular outbreak strains
of the virus and then finding their origin by matching them to sample strains
obtained worldwide. In addition, it has
been a leader in providing American funding for immunization campaigns and
surveillance activities. Furthermore,
many other organizations have been actively involved in the campaign such as the
International Red Cross and Red Crescent, Adventis Pasteur, Save the Children,
CARE, Medecins sans frontiers, plus many additional groups. And as mentioned, governments of polio
endemic countries have also played a key role, committing substantial
resources.
Maintaining the “cold chain” in the former Zaire, by Sabastiao Salgado, Brazilian photographer
http://www.endofpolio.org/home.html
An action plan
After its success in the Americas,
WHO identified several important strategies for worldwide polio
eradication. The first was to achieve
or maintain high vaccine coverage which theoretically would be 90% (but not always
possible due to various reasons to be discussed later). The second was the necessity of National
Vaccination Days (NID’s). This was a
mass campaign countrywide within endemic areas where all children less than 5,
regardless of previous immunization status, would be ideally vaccinated twice,
with the two respective doses one month apart.
They must be implemented effectively over a period of three years to
eliminate transmission.
NID’s in Afghanistan by Sabastiao Salgado, Brazilian photographer
http://www.endofpolio.org/home.html
The third point was the continued
surveillance for acute flaccid paralysis (AFP). Here individual country health officials investigate any child
under the age of 15 with a paralyzed limb, testing his stool sample for polio
infection.
Finally, the last was what was
designated the “mop-up” campaign with house to house immunizations among the
last areas the virus is seen to put a complete stop to transmission. This would be in addition to the NID’s.
Where do we stand today?
Current areas of endemic polio are
India, Pakistan, Afghanistan, and parts of the African region. In 2000, there were 20 countries still affected,
with only 10 in 2001. Below one can see
the spread of new wild type cases in 2002 and 2001, respectively--
http://www.whoafro.org/polio/surveillance_maps/wp2001-2002.html
As mentioned, much progress has been
made as polio eradication has received more and more attention and
priority. NID’s increased significantly
throughout African countries after 1996 when Nelson Mandela launched his own
“Kick polio out of Africa” campaign.
This, in effect, helped rally all of Africa with 28 of its countries
participating in NID’s by the end of 1996.
This had happened previously in China with President Jiang Zemin’s
initiative, as well as in Latin America.
Truly, politics has played a key role in the eradication progress; it
can only be achieved with the necessary political and financial support according
to a perspective on the eradication campaign (Hull, 1).
Furthermore, these individuals
suggest that the most significant factor in achieving success is the political
commitment and accompanying infrastructure within the endemic countries (Hull,
2). Similarly, Dr. Robbins cites lack
of funds and infrastructure, in addition to conflict as being significant
barriers, as opposed to lack of appropriate technologies or treatments.
Indeed, many of the hurdles have
stemmed from unstable regimes and war; at such times of conflict, it is
understandably difficult to conduct such a vast immunization campaign. And lapses in immunization can bring about a
return of the virus in a population that has not seen polio recently. In 2000 for instance, Cape Verde had not had
a case for a decade but when a traveler from Angola immigrated there carrying
the virus, 44 people were paralyzed and another 17 dead due to the vast
underimmunization (www.endofpolio.org). And to a lesser extent, Burkina Faso had not
seen a case since 1997 but then had another confirmed infection December of
2002. Truly, as long as one case of
polio remains, all remain potentially at risk.
Polio eradication remarkably has
been able to bring many people together and to momentarily put aside
hostilities in order to hold mass vaccination campaigns. This first happened in El Salvador in 1985,
met with successful results. Warring
Sierra Leone also had a similar cease-fire to implement mass vaccination in 1999. Many other nations have followed suit--Afghanistan,
the Democratic Republic of Congo, Cambodia, India, and Iraq to name a few.
In each of these instances, the
results were only possible with support from WHO, its collaborating agencies,
as well as local NGO’s. They worked
closely with the warring factions to bring about the necessary cease-fires
required for the NID’s and mop up campaigns in areas of open conflict, as well
as helping establish some sort of infrastructure for immunizations in areas suffering
from the aftermath of conflict (e.g., helping organize refugees and internally
displaced persons as well as aiding the remaining health care workers). Once more, politics is at the forefront of
the campaign.
Looking to the future
Today, India, Pakistan, and Nigeria maintain the highest rates of wild virus. In 2002, there was a total of nine countries with confirmed wild-type cases. Furthermore, while other countries saw a decrease in cases, India and Nigeria actually saw an increase with that in India being more pronounced; in fact, the vast majority of known wild type cases were traced to these two nations.
The Global Technical Consultative Group for Poliomyelitis
Eradication (TCG) reported some concern in these findings. They hypothesized that in the other
countries with incident cases appeared to have sufficient supplementary
immunization activities (SIA’s—“mop up” activities) to stop polio transmission
by 2003 but that India and Nigeria, in addition to Egypt, needed to augment
their current efforts and indicated that closing these immunization gaps would
require urgent and substantial work to put an end to transmission. They need to follow the lead of Pakistan,
one of the remaining “high transmission” countries, which has had consistent quality
SIA’s each progressive year (Polio News,
December 2002).
India did a good job with its
immunization campaigns in 1999-2000 but has recently faltered in its
consistency of SIA’s (having only 2 for the entire year) resulting in five
times as many cases in 2002 compared to 2001.
However, India has just launched the largest ever immunization campaign
last February and officials are hopeful.
Nigeria, too, only had 2 SIA’s. This and its lack of local health
infrastructure commitment and organization, according to TCG, contributed to
their increase in wild-type incidence (Polio
News, December 2002).
India and Nigeria need to focus on
their health infrastructure, planning regular NID’s, as well as accurately
reporting cases of AFP in accordance with the established WHO guidelines for
eradication. To be successful, the
governments must keep eradication as a priority and work closely with their
medical and community leaders, as well as closely collaborating with the
aforementioned partner agencies.
As a health official in a rural
province in India, one would want to keep an active surveillance for any
possible cases (i.e., keeping a careful watch with the help of community
leaders for AFP). If a case is spotted,
it must be immediately reported to the WHO and partner agencies, as well as the
Indian ministry of health to enlist the help of epidemiologists and additional
health workers. They would then, in
turn, look for any other cases of AFP while at the same time immediately
testing the AFP case’s stool for polio virus.
One would also want to schedule additional “mop up” vaccinations among
those in close contact with him or her, as well as those in surrounding
communities. Only with such active and
persistent surveillance, in addition to regularly scheduled NID’s can these
remaining nations eliminate polio.
And in fact, this is what has been
planned for India and other remaining countries at risk. Furthermore, India reported most recently in
the Polio News (March, 2003) that
they are strengthening their outreach efforts as well (e.g., activities for
educating and mobilizing individual communities regarding the importance of
immunization efforts and surveillance).
Wild card
One thing
polio has taught us recently is never to be too confident and to expect the
unexpected. The Americas had not seen a
wild type case in almost a decade. However,
in 2000, almost unbelievably, an outbreak of paralytic polio appeared in the
island of Hispaniola (i.e., throughout the Dominican Republic and Haiti). It was hypothesized to be a mutated form of
the Sabin vaccine virus and was thus able to be so readily transmitted (e.g.,
it had reverted to something resembling the wild type virus). In fact, its isolated strain was found to be
a 97% match with the OPV (Vastag, 2798).
Furthermore, due to the underimmunized status of the population, the
virus was easily able to infect many.
Fortunately in this case, though, epidemiologists and health workers
were able to immunize and treat those in close proximity to the infected,
thereby containing the out break.
However, this is certainly a concern for the future. Can we simply abruptly cease all
immunization as planned once eradication is declared, with the threat of a
lingering OPV? Or do we continue to
immunize the world but via IPV which might not be a practical goal as the
vaccine is much more expensive and more complicated to administer?
There are certainly ethical issues
as well—would it be right to risk continued use of OPV in the developing world
but keeping the IPV for those of us who are able to have access to the
IPV? Fortunately, this instance in
Hispanola is considered extremely rare, with only two other such outbreaks
documented (and with significantly lower incidence).
And, as Paul Fine and Ilona Carneiro
concur, it is very difficult to predict what will happen; hence, there is no
easy answer. Therefore, one must
continue to maintain active surveillance and gather data while at the same time
preparing several contingency plans in the event of further OPV-related
outbreaks (1019).
Possible bioterrorism agent?
Could polio
follow smallpox’s suit, one might wonder, particularly as eradication becomes
more and more of a possibility?
Actually, polio is not a pathogen of choice for bioterrorism. Unlike anthrax, smallpox, plague, and
others, it can only be transmitted via the oral/fecal route and thus cannot be
dispersed aerially (i.e., in this regards it is not nearly as contagious a
pathogen).
Nearing the end—is 2005 realistic?
So, one asks Dr. Robbins, will this
really come to pass? Actually, as he
explained to me, the original 2000 date was just a standard to work toward; rather,
it was not derived from any sort of epidemiological algorithm (2005, as well). And this adjusted deadline is theoretically
possible--but of course, eradication would not be officially declared until
three years after the last documented case according to WHO guidelines, moving
the official eradication time to 2008--as long as there were no significant
disruption of activities. However, disruptions
cannot be overlooked considering the precarious state of affairs in the world
today, particularly in areas where the virus is still endemic. Yet many unlikely partnerships have been
formed and factions unified throughout this campaign, so it is quite possible the
campaign will persevere as it has so far.
Now, though, it is extremely
important that endemic countries continue with their immunization campaigns to
put an end to disease transmission altogether as previously mentioned. In addition, WHO and the other
collaborators must continue to work closely with individual health ministries
to assure that NID’s and supplemental immunization activities are consistently
and appropriately conducted, particularly in regions of conflict. And finally, and perhaps most importantly,
we must continue to keep polio in the forefront of international policy, as
politics is such an integral determinant of the campaign’s success. After all, there is an effective vaccine
available—it’s just the distribution that’s so difficult.
References
Bruno, Richard. The Polio Paradox: What You Need to Know. New York:
Warner
Books, 2002.
Daniel, Thomas M and Robbins, Frederick
C. Polio. Rochester: University
of
Rochester Press, 1997.
Fine, Paul EM and Carneiro, Ilona AM. Transmissibility and persistence of
oral
polio
vaccine viruses: Implications for the
global eradication initiative. American
Journal of Epidemiology 1999; 150 (10): 1001-1021.
Francis, Thomas, Napier, John A., Voight,
Robert B, et al. Evaluation of
the
1954 Field Trial of Poliomyelitis
Vaccine. Ann
Arbor: Edward Brothers, Inc, 1957.
Global Polio Eradication Initiative: Summary Report
of 2001 Progress on the
2001-2005 Global Strategic Plan
for Poliomyelitis Eradication. Geneva: World Health Organization, 2002.
Gould, Tony.
A Summer Plague: Polio and its Survivors. New Haven: Yale
University
Press, 1995.
Hull, HF, DeQuadros, C., et al. Perspectives from the Global Poliomyelitis
Eradication
Initiative. MMWR: December 31, 1999.
Last, John
M. and Wallace, Robert B. Public Health and Preventive Medicine.
Norwalk, CT: Appleton & Lange, 1992, 13th
edition.
Nathanson, Neal and Fine, Paul. Poliomyelitis eradication—a dangerous
Endgame. Science 2002; 296: 269-270.
Robbins, Frederick C. Interview: April 4, 2003.
Smith, Jane.
Patenting the Sun: Polio and the Salk Vaccine. New York: William
Morrow,
1990.
Vastag, Brian. At polio’s end game, strategies differ. JAMA 2001; 286 (22):
2797-2799.
www.cdc.gov/nip/publications/pink/polio.pdf,
background information on polio.
www.endofpolio.org,
general polio eradication data from WHO, UNICEF, Rotary
International,
and the CDC.
www.whoafro.org/polio/surveillance_maps/wp2001-2002.html
, recent wild virus
surveillance
data.
www.who.int/vaccines-polio/all/news/files/pdf/polionews2003march18.pdf,
Polio
News.
www.whoafro.org/polio/certificationcriteria.html
, eradication criteria status per
country update
www.whoafro.org/polio/afp_indicators/dec02_as_19feb_03.htm
, recent AFP surveillance data.
www.whoafro.org/polio/index.html
, general WHO data on polio eradication.
More general
websites:
www.rotary.org/foundation/polioplus/