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Global Health Observatory
Short name:
Large/disruptive VPD outbreaks
Data type:
Count
Topic:
Immunization and Outbreak Response
Rationale:
Global, regional, and country partners can use evaluation findings for operational planning, and for communication and advocacy to: ensure timely availability and strategic allocation of vaccines and supplies, mobilization of trained human resources for outbreak response; ensure capacity of immunization programmes to anticipate, prepare for, detect and rapidly respond to VPD and emerging disease outbreaks; establish timely and appropriate immunization service delivery during emergencies and in communities affected by conflict, disaster and humanitarian crisis; ensure vaccine introduction and scale up of coverage to prevent newly emerging VPDs; use measles cases and outbreaks as a tracer to identify weaknesses in immunization programmes, and to guide programmatic planning in identifying and addressing these weaknesses.
Definition:
The number of large or disruptive outbreaks of vaccine-preventable diseases (VPDs)*occurring within a calendar year, reported by WHO and verified through surveillance and outbreak reporting systems.

A VPD outbreak meeting size criteria for large or disruptive outbreaks aligned with global VPD strategies and at least one criterion from Annex 2 of the International Health Regulations (https://www.who.int/ihr/annex_2/en/)

*Including measles, wild poliovirus, circulating vaccine derived poliovirus, meningococcus, yellow fever, cholera, and Ebola, the list could be revised, especially as additional diseases become vaccine preventable.

Associated terms:
• Vaccine-Preventable Diseases (VPDs): Diseases for which effective vaccines exist including measles, wild poliovirus, circulating vaccine derived poliovirus, meningococcus, yellow fever, cholera, and Ebola.

• Large Outbreak: A VPD outbreak that exceeds a predefined threshold of scale, geographic spread, or case count (e.g., >1,000 cases).

• Disruptive Outbreak: An outbreak that severely impacts public health systems, services, or communities (e.g., requires international support, leads to school closures, etc.).

• International Health Regulations (IHR): WHO’s legal framework that mandates countries to report and respond to significant public health risks, including outbreaks.

Disaggregation:
WHO Region

VPD Types

Method of measurement
Large or disruptive VPD outbreaks are identified using data from specific VPD control programmes and from WHO World Health Emergencies surveillance systems. Different criteria were applied for each disease. For multi-country outbreaks, each country’s portion of the outbreak was assessed separately. The overall indicator will function as a composite combining data across the different diseases.
Method of estimation:
A collective count of outbreaks of epidemic prone diseases that meet set size criteria, such as the number of cases or disease incidence.

Definition of large or disruptive outbreaks:

+ Measles: Incidence equal to or greater than 20 reported measles cases per million total (all ages) national (not restricted to region or area or ethnic/religious/cultural community in which cases occurred) population over a rolling period of 12 months

+ Wild poliovirus: > 1 WPV from any source (e.g., cases, environmental surveillance, contacts, healthy children's samples) in a country per year AND confirmation of local circulation in accordance with the standard operating procedures for outbreak response.

+ Circulating Vaccine Derived Polio Virus: > 1 cVDPV from any source (e.g., cases, environmental surveillance, contacts, healthy children's samples) in a country per year AND evidence of local circulation in accordance with the standard operating procedures for outbreak response.

+ Cholera (Highly Endemic countries): A threshold increase in the annual number of reported cases compared to the average annual incidence over the past 5 years.

+ Cholera (Endemic-Epidemic countries): Over 12,000 cases reported annually.

+ Meningococcus: A cumulative attack rate >100 suspected meningitis cases per 100,000 population within one year in each population based on a definition used for the African meningitis belt. Each region will set its own definitions for epidemics/outbreaks and targets for reduction according to local epidemiology.

+ Yellow Fever (Endemic area): 5 or more cases in endemic areas.

+ Yellow Fever (Non-Endemic area): >1 cases in an area previously without yellow fever

+ Ebola: >50 cases

Method of estimation of global and regional aggregates:
Sum
Preferred data sources:
VPD eradication, elimination, and control programmes and the WHO World Health Emergencies surveillance systems
Unit of Measure:
Outbreaks
Unit Multiplier:
N/A
Expected frequency of data dissemination:
Annual
Expected frequency of data collection:
Annual
Contact person email:
vpdata@who.int
Name:
-
Data Type Representation:
Integer
IMRID:
7774
Limitations:
+ Variability in what countries consider a “large” or “disruptive” outbreak without standardized thresholds

+ Underreporting or delayed reporting in countries with weak surveillance

+ Attribution to VPDs may be incomplete where lab confirmation is lacking

+ Multiple outbreaks in one country may reflect systemic issues not visible from raw counts

Links:
IA2030 Annex 1: Monitoring and Evaluation Framework || https://immunizationagenda2030.org/images/documents/IA2030_Annex_FrameworkForActionv04.pdf
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