Immunization, Vaccines and Biologicals

WHO-recommended surveillance standard of poliomyelitis

Rationale for surveillance

Poliomyelitis is targeted for eradication. Highly sensitive surveillance for acute flaccid paralysis (AFP), including immediate case investigation, and specimen collection are critical for the detection of wild poliovirus circulation with the ultimate objective of polio eradication. AFP surveillance is also critical for documenting the absence of poliovirus circulation for polio-free certification


Recommended case definition

Clinical case definition

Any child under 15 years of age with AFP* or any person of any age with paralytic illness if polio is suspected

Case classification

Suspected case: A case that meets the clinical case definition
Confirmed case: See diagram in special aspects section

*Including Guillain-Barré syndrome


Recommended types of surveillance
  • Aggregated data on AFP cases should be included in routine monthly surveillance reports
  • Designated reporting sites at all levels should report at a specified frequency (e.g. weekly or monthly) even if there are zero cases (often referred to as "zero reporting")
  • All outbreaks should be investigated immediately
  • All AFP cases under 15 years of age or with paralytic illness at an age where polio is suspected should be reported immediately and investigated within 48 hours, and two stool specimens should be collected 24-48 hours apart and within 14 days of the onset of paralysis
  • Active surveillance: Regular weekly visits should be made to selected reporting sites that are most likely to admit acute flaccid paralysis patients (e.g. major hospitals, physiotherapy centers) to look for unreported AFP cases

Recommended minimum data elements

Aggregated data

  • Number of third doses of oral polio vaccine (OPV3) administered to infants
  • Number of AFP cases

Case-based data

(to be linked to specimen-based data for analysis)

  • Unique identifier
  • Geographical area (e.g. district and province names)
  • Date of birth
  • Sex: 1 = male; 2 = female; 9 = unknown
  • Date of paralysis
  • Date of notification
  • Date of case investigation
  • Total polio vaccine doses received: 99 = unknown
  • Fever at onset of paralysis: 1 = yes; 2 = no; 9 = unknown
  • Progression of paralysis within four days: 1 = yes; 2 = no; 9 = unknown
  • Asymmetric paralysis: 1 = yes; 2 = no; 9 = unknown Date of 60-day follow-up examination
  • Findings at 60-day follow-up: 1 = residual weakness; 2 = no residual weakness; 3 = lost to follow-up; 4 = death before follow-up; 9 = unknown
  • Final classification: 1 = confirmed; 2 = compatible; 3 = discarded

Specimen-based data

(to be linked to case-based data for analysis)

  • Unique identifier
  • Specimen number: 1 = first specimen; 2 = second specimen; 3 = other; 9 = unknown
  • Date of onset of paralysis
  • Date of last OPV dose
  • Date of collection of stool specimen
  • Date stool specimen sent to laboratory
  • Date stool specimen received in laboratory
  • Condition of stool: 1 = good; 2 = poor; 9 = unknown
  • Date final culture results sent from laboratory to EPI
  • Date intratypic differentiation results sent from laboratory to EPI
  • Results
    - Polio type1 isolated? 1 = yes, wild; 2 = yes, Sabin; 3 = yes, pending intratypic differentiation; 4 = yes, mixture of wild and Sabin; 5 = no polio type 1 isolated; 6 = specimen not processed; 9 = unknown
    - Polio type 2 isolated? 1 = yes, wild; 2 = yes, Sabin; 3 = yes, pending intratypic differentiation; 4 = yes, mixture of wild and Sabin; 5 = no polio type 2 isolated; 6 = specimen not processed; 9= unknown
    - Polio type 3 isolated? 1 = yes, wild; 2 = yes, Sabin; 3 = yes, pending intratypic differentiation; 4 = yes, mixture of wild and Sabin; 5 = no polio type 3 isolated; 6 = specimen not processed; 9 = unknown
    - Non-polio enterovirus (NPEV) isolated? 1 = yes; 2 = no NPEV isolated; 3 = specimen not processed; 9 = unknown

Recommended data analyses, presentations, reports

Aggregated data

  • Cases and incidence rate by month, year and geographical area
  • OPV3 coverage by year and geographical area
  • Completeness/timeliness of monthly reporting

Case-based data

same as aggregated data plus the following:

  • Confirmed cases by age group, sex, immunization status, geographical area, month and year
  • Confirmed cases from which wild poliovirus was isolated, by geographical area, sex, month and year
  • Compatible cases by geographical area and month
  • All suspect cases by final classification
  • Non-polio enterovirus isolation rate
  • Indicators of surveillance performance
    - Percentage of all expected monthly reports that were received: target >=90%
    - Annualized non-polio AFP rate per 100 000 children under 15 years of age: target >=1/100 000
    - Percentage of AFP cases investigated within 48 hours: target >=80%
    - Percentage of AFP cases with two adequate stool specimens collected 24-48 hours apart and <=14 days after onset: target >=80%
    - Percentage of specimens arriving at the laboratory in good condition: target >=80%
    - Percentage of specimens arriving at a WHO-accredited laboratory within three days of being sent: target >=80%
    - Percentage of specimens for which laboratory results sent within 28 days of receipt of specimens: target >=80%

Principal uses of data for decision-making
  • Track wild poliovirus circulation
  • Use data for classifying cases as confirmed, polio-compatible or discarded (see special aspects section)
  • Monitor routine coverage, as well as performance of surveillance (by means of the standard indicators listed above) in all geographical areas and focus efforts in low-performing geographical areas
  • Monitor seasonality to determine low season of poliovirus transmission in the interest of planning national immunization days (NIDs)
  • Identify high-risk areas with a view to planning mop-up immunization campaigns
  • Provide evidence to certification commissions of the interruption of wild poliovirus circulation

Special aspects

The scheme in the following illustration should be used to classify AFP cases. Countries should use the clinical classification until their surveillance performance meets the following three criteria:

  • a non-polio AFP rate of at least 1/100 000 children under 15 years of age
  • two adequate specimens* collected from at least 60% of detected AFP cases
  • all specimens processed in a WHO-accredited laboratory

Final classification scheme for AFP cases

*Collected 24-48 hours apart and within 14 days of the onset of paralysis. Specimens arriving in the laboratory must be of adequate volume (approximatively 8-10g), have appropriate documentation (i.e. laboratory request form) and be in good condition, i.e. with no leakage or dessiccation and with evidence that the reverse cold chain has been maintained (presence of ice or temperature indicator).
2: compatible cases indicate surveillance failures and should be monitored for clustering in space and time


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