Polio basics

Even though you might think that polioviruses are gone because you might not hear much about them, they still pose a very real threat in a few parts of the world and they could return to wider circulation if we do not eradicate them.

Frequently asked questions

What are polioviruses?
What do polioviruses do to people?
What tools do we use to protect ourselves from polioviruses?
What is happening with respect to global polio eradication?
What are the similarities and differences between polio eradication and smallpox eradication?
What can you do to help eradicate polio?
Common abbreviations

What are polioviruses? (get more information about this from the World Health Organization and the U.S. Centers for Disease Control and Prevention)

Three-dimensional structure of poliovirus at 2.9 Å resolution. Hogle, JM, M Chow, and DJ Filman. Science 1985; 229:1358-1365. Shown with permission from Professor J. Hogle.

Three-dimensional structure of poliovirus receptor bound to poliovirus. Belnap, DM, BMJ McDermott, DJ Filman, N Cheng, BL Trus, HJ Zuccola, VR Racaniello, JM Hogle, and AC Steven. Proc. Natl. Acad. Sci. 2000;97:73-78. Shown with permission from Professor DM Belnap.

What do polioviruses do to people?

What tools do we use to protect ourselves from polioviruses?

What is happening with respect to global polio eradication? (quoted and paraphrased from Thompson KM. Poliomyelitis and the role of risk analysis in global infectious disease policy and management. Risk Analysis 2006;26(6):1419-1421).

In 1988 estimates of the annual number of cases of paralytic polio were approximately 250,000 and wild polioviruses were circulating in over 125 countries. Given this large burden and demonstrated successful elimination of wild polioviruses in the Americas, the World Health Assembly committed to global eradication of wild polioviruses by the year 2000. Although the goal of eradication has yet to be achieved, the Global Polio Eradication Initiative (GPEI) has made remarkable progress and reduced the number of cases of paralytic polio to fewer than 2,000 cases per year (with endemic circulation remaining in only Afghanistan, Nigeria, Pakistan, and northern India). Challenges in these remaining endemic areas differ: vaccine campaigns in India continue to miss children (particularly in minority populations), campaigns in Nigeria suffer from operational and political issues, and campaigns in Afghanistan and Pakistan are limited by security issues associated with current conflicts. In addition, during the past several years, the challenges to successfully eradicating wild polioviruses and our knowledge of them increased as new risks emerged. Notably, as some polio-free countries reduced or eliminated their use of live oral poliovirus vaccine (OPV), local outbreaks occurred due to neurovirulent circulating vaccine-derived polioviruses (cVDPVs). These experiences reveal that OPV circulating through populations with enough susceptible individuals can mutate back toward wild poliovirus and cause paralysis. Consequently, eradicating virulent polioviruses will eventually require stopping the use of OPV, which is currently the vaccine of choice for the GPEI due to its low cost, population immunity benefits, and ease of administration. Thus, the GPEI and national health leaders now confront the challenge of encouraging high coverage with OPV to finish the job of eradication and increase population immunity prior to OPV cessation, while at the same time they must begin plans for coordinated OPV cessation and pursue eradication in the context of numerous competing opportunities for scarce health resources. Adding more complexity, modern technology now supports the ability to synthesize poliovirus in a laboratory, a demonstrated reality recognized not long after the events of 9/11 altered perceptions about the potential risks of intentional events (at least for some individuals and countries). Finally, the existence of a small number of immunodeficient individuals who continue to excrete polioviruses they did not clear after receiving OPV raises the possibility of these viruses (called iVDPVs) potentially infecting susceptible individuals. Incidental discovery of just such a virus from an unidentified source in an asymptomatic child in Minnesota recently raised awareness of this risk. Given these challenges, the GPEI is working to interrupt all remaining chains of transmission as quickly as possible and is starting to plan to manage the risks of polioviruses following the complete and sustained interruption of circulating wild polioviruses. The GPEI provides current case counts and maps.
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What are the similarities and differences between polio eradication and other eradication campaigns?

What can you do to help eradicate polio?

Common abbreviations

Abbreviations we use:

Ab = neutralizing antibody (generic term)
AFP = acute flaccid paralysis
aVDPV = ambiguous vaccine-derived poliovirus
bOPV = bivalent oral poliovirus vaccine (types 1 and 3)
cVDPV = circulating vaccine-derived poliovirus (cVDPV1, cVDPV2, and cVDPV3 indicating circulating vaccine-derived poliovirus types 1, 2, and 3, respectively)
CDC = U.S. Centers for Disease Control and Prevention
CID50 = cell- or tissue-culture infectious doses
CVID = Common variable immunodeficiency
DTP = Diphtheria and Tetanus toxoids and Pertussis vaccine
DTaP = Diphtheria and Tetanus toxoids and acellular Pertussis vaccine
DTwP = Diphtheria and Tetanus toxoids and whole-cell Pertussis vaccine
eIPV = enhanced-potency inactivated poliovirus vaccine
EIP = effective immune proportion
EIP* = threshold level of EIP below which a population can sustain transmission
ESP = effective susceptible proportion
ESP* = threshold level of ESP above which a population can sustain transmission
FRPV = fully-reverted poliovirus
FS = fully susceptible (immunity state)
GPEI = Global Polio Eradication Initiative
Hep = hepatitis B
Hib = Haemophilus influenzae type b conjugate vaccine
GPEI = Global Polio Eradication Initiative
HIGH = high-income country
IgA = immunoglobulin A
IgG = immunoglobulin G
IgM = immunoglobulin M
IPV = inactivated poliovirus vaccine
IPV1 = 1 successful IPV dose (immunity state)
IPV2 = 2 successful IPV doses (immunity state)
IPV3 = 3 or more successful IPV doses (immunity state)
IPVLPV = IPV and LPV (i.e., one or more successful IPV doses and 1 or more LPV infections) (immunity state)
IU = international units
iVDPV = vaccine-derived poliovirus from an immunodeficient individual
LMI = lower-middle-income country
LOW = low-income country
LPV = live poliovirus (WPV, VDPV, and/or OPV)
LPV1 = 1 LPV infection (immunity state)
LPV2 = 2 or more LPV infections (immunity state)
MK = monkey kidney tissue culture
mOPV = monovalent OPV (mOPV1, mOPV2, and mOPV3 indicating monovalent types 1, 2, and 3, respectively)
MPI = maximum population immunity scenario
mOPV = monovalent oral poliovirus vaccine
NA = not applicable
ND = not done
NID = national immunization day
NR = not reported
OPV = oral poliovirus vaccine (generally trivalent unless otherwise specified)
PCR = polymerase chain reaction
pfu = plaque-forming unit
PO = proportion of transmissions via oropharyngeal route
PV = poliovirus (PV1, PV2, and PV3 indicate poliovirus types 1, 2, and 3, respectively)
R0 = basic reproductive number
RCFTI = relative contribution to fecal-oral transmission if infected
RCOTI = relative contribution to oropharyngeal transmission if infected
RT-PCR = reverse transcriptase PCR
SIR = susceptible-infected-removed
RPI = realistic population immunity scenario
SES = socio-economic status
SIA = supplemental immunization activity
SNIDs = subnational immunization days
Sr = relative susceptibility
TIAs = targeted immunization activities
tOPV = trivalent oral poliovirus vaccine
UK = United Kingdom
UMI = upper-middle-income country
USA = United States of America
VAPP = vaccine-associated paralytic polio
VDPV = vaccine-derived poliovirus
VP1 = viral protein 1
WHA = World Health Assembly
WHO = World Health Organization
WPV - wild poliovirus (WPV1, WPV2, and WPV3 indicate wild poliovirus types 1, 2, and 3, respectively)
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