Polio eradication

Question 1

Reasons Polio can be eradicated

Answer 1

• Polio only affects humans, and there is no animal reservoir
• An effective, inexpensive vaccines exists → OPV + IPV
• Immunity is life-long
• There are no long-term carriers (this point isn’t completely true)
• The virus cannot survive for long outside the body.

Question 2

Major aspects of polio eradication strategy

Answer 2

• The polio eradication strategy is based on the premise that poliovirus will die out if deprived of its human host thru immun.
• The strategy developed by WHO to eradicate polio is four-pronged:

1. Routine immunization with OPV → 3 doses, everyone.
2. Additional doses of oral poliovaccine during National Immunization Days
3. Enhanced surveillance for all cases of acute flaccid paralysis (AFP) and wild–type poliovirus
4. Mopping-up immunization activities.

Question 3

Characteristics of routine immunization w/OPV

Answer 3

• WHO Expanded Program on Immunization (EPI),
  
  • global target of at least 90% immunization coverage by the year 2000
  • diphtheria, tetanus, whooping cough, tuberculosis, measles, and polio.
• When polio has been eradicated globally, immunization against polio will no longer be needed.
• In the meantime, regions and areas where polio eradication has been achieved must continue to maintain high levels of polio immunization to prevent the re-establishment

Question 4

Characteristics of additional dosing of polio vaccine

Answer 4

• Additional doses of oral poliovaccine during National Immunization Days
• Complements routine immunization
• The aim = interrupt circulation of poliovirus by immunizing every child under 5 years of age with two doses of OPV, regardless of previous immunization status.
• The idea is to catch children who are either not immunized, or only partially protected, and to boost immunity in those who have been immunized.
• Three to five years of NIDs are usually required to eradicate polio, but some countries require more time, especially those where routine immunization coverage is low.
• conducted during the cool, dry season because logistics are simplified, immunological response to OPV is improved and the potential damage to heat-sensitive OPV is reduced.

Question 5

Characteristics of enhanced surveillance for acute flaccid paralysis

Answer 5

• AFP case identification → Health care workers who notice virus need to report all cases
• Stool specimen collection from AFP cases
• Virus isolation/identification in the laboratory
• Without AFP surveillance, poliovirus is difficult to find because fewer than 1% of polio infections ever result in paralysis. most = mild
• polio may be difficult to differentiate

Question 6

Characteristics of stool specimin collection from AFP cases

Answer 6

• Because shedding of the virus is variable, two specimens taken 24-48 hours apart are required for analysis.
• Samples must be obtained soon after the onset of paralysis.
• Stool specimens must be carefully sealed in containers and stored immediately inside a refrigerator or packed between frozen ice packs at 4-8 oC in a cold box, ready for shipment to a laboratory.

Question 7

Characteristics of viral isolation/identification from AFP cases

Answer 7

• Culture viruses
• Establish which serotype of poliovirus is present
• If poliovirus is isolated, the next step is to distinguish between wild-type (naturally occurring) poliovirus and vaccine-related poliovirus. Use ELISA or PCR.

Question 8

Characteristics of STR

Answer 8

• When very few or no cases of polio occur, the final strategy of the four- pronged approach is implemented.
• This involves door-to-door immunization (“mopping up”) in high-risk districts where the virus is known or suspected still to be circulating.
• Priority districts include those where polio has occurred over the previous three years and where access to health care is difficult.
• Other criteria include overcrowding, high population mobility, poor sanitation, and low routine immunization coverage.

Question 9

How effectively is universal vaccination with OPV being implemented worldwide and in specific subpopulations?

Answer 9

~83% worldwide. 0% to 100% in subpopulations.

Question 10

1. Where is virulent wildtype poliovirus currently circulating?
2. How many cases of poliomyelitis have been reported annually?
3. How many cases of acute flaccid paralysis have been reported annually?
4. How many doses of OPV are being used annually?

Answer 10

1. SE Asia, Africa (Pakistan, Afghanistan, Nigeria, etc)
2. ~1,000 to 2,000 per year over past decade. 650 in 2011.
3. Greater than 100,000 in 2011
4. Greater than 2 billion doses annually in recent years (2000 through 2009). mOPV & bOPV now commonly used in addition to tOPV

Question 11

Cultural, political, economic and scientific obstacles that, to date, have prevented poliovirus eradication

Answer 11

• Cultural & Political
  
  • Improved intergovernmental relationships could diminish animosity that leads to unfounded fear and lack of trust.
• Economic
  
  • Better sewage treatment and water treatment might be more cost effective than additional vaccinations because diminished fecal-oral transmission would be advantageous in areas where such transmission is rampant due to the lack of such infrastructure
• Scientific
  
  • Reversion of OPV strains along with transmission in the environment (cVDPV) is a huge problem.
  • Requirement for needles with IPV is a huge disadvantage in many parts of the world where needles tend to be re-used…spread parenteral infectious diseases (HIV, HCV, etc..).

Question 12

Obstacles and Problems with the eradication strategy

Answer 12

• How long can poliovirus be shed from agammaglobulinemic individuals?
• Greater than 10 years
• What may happen to OPV vaccine strains when poliovirus vaccination ceases?
• Fecal-oral transmission from person-to-person…reversion…epidemics of VAPP.
• What technologies allow for the de novo re-creation of poliovirus?
• DNA oligonucleotide synthesis, recombinant DNA technology.