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Polio Eradication

Polio Eradication. Dr Marvin Hsiao Division of Medical Virology NHLS/UCT/Groote Schuur Hospital. The virus. Single strand positive sense RNA virus Non-enveloped Family Picornaviridae Genus Enterovirus 3 types, poliovirus 1-3 Grows well in cell culture. The pathogenesis.

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Polio Eradication

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  1. Polio Eradication Dr Marvin Hsiao Division of Medical Virology NHLS/UCT/Groote Schuur Hospital

  2. The virus • Single strand positive sense RNA virus • Non-enveloped • Family Picornaviridae • Genus Enterovirus • 3 types, poliovirus 1-3 • Grows well in cell culture

  3. The pathogenesis • Faecal oral transmission (+respiratory) • Replicate in the lymphoid tissue in throat and gut - Viraemia • Replication in neuronal cell – especially motor neuron in spinal cord (polios: grey muelos: marrow) • Lytic infection of neurons • Anterior horn cell • Axon degeneration • LMN (flaccid) paralysis

  4. The disease Adapted from Collier & Oxford Human Virology 2nd Edition Poliovirus infection asymptomatic Mild Febrile Illness Full recovery Meningitic Stage Post polio syndrome Acute Flaccid Paralysis (+/-1%) Death

  5. The vaccines

  6. The vaccines *VAPP = Vaccine associated paralytic poliomyelitis

  7. Levels of epidemiological modification by vaccination

  8. The campaign • 1988 World Health Assembly passed a resolution to eradicate polio by 2000 • The Global Polio Eradication Initiative was founded – Biggest Public health initiative to date • Task: co-ordinate eradication of poliovirus globally and source funding

  9. Global Status 1988 http://www.polioeradication.org/ 350 000 cases polio-1988 125 polio-endemic countries

  10. Global Status 2004 http://www.polioeradication.org 1,263 cases in 2004 (99% reduction in cases) 1000 childhood paralysis prevented per day 6 polio-endemic countries, 5 countries re-established transmission

  11. Science 26 March 2005 vol 303

  12. The challenges • Funding gap • Containing polio in endemic area • Nigeria • Uttar Pradesh and Bihar states in NE India • Containing polio epidemics due to importation (Namibia) • Vaccine derived polio viruses (VDPV) • Laboratory containment

  13. Polio endemic area • Nigeria • Overcoming political and religious resistence • Vaccination campaign back on track • India • High intensity of polio transmission combined with high incidence of enteric disease • Despite good coverage unable to interrupt transmission of polio • Monovalent vaccine (response to single dose mOPV is >75% compare to tOPV 25%)

  14. The Namibian experience • Prior to the outbreak • Started OPV 1990, coverage of 60-80% • Last case of polio reported 1996 • AFP surveillance: 2.6/100,000 and 86% stool collection rate (adequate) • The outbreak: • Index case May 2006 • 185 suspected cases • 20 laboratory confirmed cases • 21 deaths, ¾ are adult over 15 years • Gaps in immunisation – a number of susceptible adults

  15. The Namibian experience • Virus identified as poliovirus type 1 SOAS genotype • Same strain as Angolan outbreak and NE states of India • Molecular distance compare to parental strain is approximately 2.5 year • Unclear whether imported from Angola or India

  16. The Namibian experience • Massive immunisation campaign targeting the entire population. • Three national immunisation days. • > 2 million doses of monovalent OPV1 administered • Outbreak halted

  17. The Namibian experience • Lessons learned: • Coverage needs to be >80% -Immunisation gap • Importance of disease surveillance • Traditional AFP surveillance on children <15 yo is inadequate marker of polio elimination • Importance of laboratory network and regional reference laboratory • Constant risk of importation • Political will – immunisation campaigns

  18. VDPV (Vaccine derived polio virus) OPV genome • <1% VP1 genetic divergence = vaccine strain (Sabin-like virus) • 1-15% VP1 genetic divergence = • Vaccine derive polio virus (VDPV) • cVDPV (evidence of circulation in the communities) • iVDPV (chronically shed by immunocompromised individuals) • >15% VP1 genetic divergence = wild polio virus 99 85

  19. The laboratory containment • A country cannot be certified as polio free unless all laboratories are free of poliovirus • If 1 country is not certified polio free, polio cannot be eradicated • Potential sources polio outbreak: • Stored stool specimen, past poliovirus isolates, polio vaccine manufacturing facility • Past enteric pathogen research specimen • Past environmental surveillance (water) samples • Past respiratory specimen (routine/research) • The “mystery” vial / Legacy of previous research in the –70 freezer

  20. Is it possible to eradicate polio? • It is possible and it has to be done • Prevent re-emergence of polio we need to: • Keep vaccinating with routine EPI and various campaigns • Good acute flaccid paralysis surveillance • Rid the laboratory of wild and vaccine poliovirus • Stop using OPV in the final phase of polio eradication • Thank you

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