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

 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

The disease

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

The vaccines

Oral Polio vaccine (OPV) Developer Albert Sabin Production Method Serial passage to attenuate strain (live) Cost cheap Route Type of immunity Oral Produce good gut immunity Inactivated Polio vaccine (IPV) Jonas Salk Formalin inactivated Tissue culture supernatant expensive IM injection Less robust gut immunity

The vaccines

Predictable immunity Revert to neuro virulence VAPP* Oral Polio vaccine (OPV) Erratic, affected by enteric disease Inactivated Polio vaccine (IPV) Predictable, not affected by enteric disease Reported. Recombination with other enteroviruses Not reported. Virus is inactivated 1 in 2.4-3.3 million Not reported Protection Contact immunity Only vaccinated individual *VAPP = Vaccine associated paralytic poliomyelitis

Levels of epidemiological modification by vaccination

Organism present ?

Surveillance Vaccination ?

?

Control Yes Low level Elimination Import only Eradication No Yes Required Yes Required No Yes Required Yes Required No

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

Global Status 1988

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

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

Science 26 March 2005 vol 303

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

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%)

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

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

The Namibian experience

 Massive immunisation campaign targeting the entire population.

 Three national immunisation days.  > 2 million doses of monovalent OPV1 administered  Outbreak halted

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

VDPV (Vaccine derived polio virus)

OPV genome 99  <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) 85  >15% VP1 genetic divergence = wild polio virus

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

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