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?
Abbreviations used in publications

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? (partly 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, at the time the World Health Assembly resolved to eradicate polio by 2000, estimates suggested approximately 250,000 cases of paralytic polio and circulation of WPVs in over 125 countries. Despite missing the target of eradicating all WPVs by 2000, the Global Polio Eradication Initiative (GPEI) continues to make remarkable progress and reduced the number of cases of paralytic polio to fewer than 2,000 cases per year by 2001. Challenges in endemic areas included missed children (particularly in minority populations), operational and political issues, and security issues associated with conflicts. In addition, the challenges to successfully eradicating WPVs and our knowledge of them increased as new risks emerged. Notably, as some polio-free countries reduced or eliminated their use of OPV, local outbreaks occurred due to neurovirulent cVDPVs. These experiences revealed that OPV circulating through populations with enough susceptible individuals can mutate back toward WPV and cause paralysis. Consequently, eradicating virulent polioviruses will eventually require stopping the use of OPV. The GPEI preferred OPV as its primary vaccine for eradication due to its low cost, population immunity benefits, and ease of administration. In the polio endgame, the GPEI and national health leaders must 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 polio 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.

In 2008, the World Health Assembly formally recognized the importance of globally-coordinated OPV cessation. With global certification of WPV2 eradication in 2015, the GPEI currently plans to coordinate cessation of OPV serotype 2 (i.e., OPV2 cessation) in April 2016. The GPEI provides current case counts and maps of reported WPVs and cVDPVs.
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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?

Abbreviations used in publications

Ab = neutralizing antibody (generic term)
AFP = acute flaccid paralysis
aVDPV = ambiguous vaccine-derived poliovirus
bOPV = bivalent oral poliovirus vaccine (serotypes 1 and 3)
CEI = Cumulative effective infection
CLS = Cost-and life-saving
CSLC = Costs aving but life-costing
CDC = U.S. Centers for Disease Control and Prevention
CID50 = cell- or tissue-culture infectious doses
cVDPV = circulating vaccine-derived poliovirus (cVDPV1, cVDPV2, and cVDPV3 indicating circulating vaccine-derived poliovirus serotypes 1, 2, and 3, respectively)
CVID = Common variable immunodeficiency
DALY = Disability-adjusted life-year
DEB = Differential equation-based
DES = Discrete-event simulation
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
E* = Threshold number of CEIs to trigger an exportation
eIPV = enhanced-potency inactivated poliovirus vaccine
EIP = effective immune proportion
EIP* = threshold level of EIP below which a population can sustain transmission
EIPM = mixing-adjusted EIP
EPI = effective proportion infectious
EPI*= transmission threshold (i.e., effective proportion infectious below which we model 0 force-of-infection in the deterministic DEB model)
ESP = effective susceptible proportion
ESP* = threshold level of ESP above which a population can sustain transmission
FRPV = fully-reverted poliovirus
FRRs = financial resource requirements
FS = fully susceptible (immunity state)
GNI = Gross national income
GPEI = Global Polio Eradication Initiative
Hep = hepatitis B component of IPV-containing combination vaccines)
Hib = Haemophilus influenzae type b conjugate vaccine
HIGH = high-income country
ICER = Incremental cost-effectiveness ratio
IgA = immunoglobulin A
IgG = immunoglobulin G
IgM = immunoglobulin M
INBs = Incremental net benefits
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)
IPV(5,10) = Global minimum policy of IPV use for (5 or 10) years
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 (i.e., 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 serotypes 1, 2, and 3, respectively)
MPI = maximum population immunity scenario
NA = not applicable
ND = not done
NID = national immunization day
NR = not reported
oPID = Other PID (i.e., not CVID PIDs)
OPV = oral poliovirus vaccine (generally trivalent unless otherwise specified)
OPV## cessation = Globally-coordinated cessation of OPV containing the serotype(s) indicated by ##
oSIA = Outbreak response SIA
PAVD(40%,90%) = Polio antiviral drug (passive or active use policy, respectively)
PCR = polymerase chain reaction
PEF = Probability of effective introduction function
pfu = plaque-forming unit
PID = Primary immunodeficiency disease
PO = proportion of transmissions via oropharyngeal route
POL3 = Coverage with 3 or more non-birth RI doses
pSIA = Planned, preventive SIA
PV = poliovirus (PV1, PV2, and PV3 indicate poliovirus serotypes 1, 2, and 3, respectively)
R0 = basic reproduction or reproductive number
RC = Reference case
RCFTI = relative contribution to fecal-oral transmission if infected
RCOTI = relative contribution to oropharyngeal transmission if infected
RCT = Relative contribution to combined fecal-oral and oropharyngeal transmission
RI = Routine immunization
Rn = mixing adjusted net reproduction or reproductive number
RT-PCR = reverse transcriptase PCR
sIPV = IPV produced from Sabin seed strains
SIR = susceptible-infected-removed
RPI = realistic population immunity scenario
SES = socio-economic status
SIA = supplemental immunization activity
SNID = subnational immunization day
Sr = relative susceptibility
T0 = Beginning of the analytical time horizon (e.g., January 1, 2013)
Tend = End of the analytical time horizon(e.g., December 31, 2052)
TIA = targeted immunization activity
tOPV = trivalent oral poliovirus vaccine
UK = United Kingdom
UMI = upper-middle-income country
US or USA = United States of America
US$#### = US dollars of the year ####
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 serotypes 1, 2, and 3, respectively)
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