Welcome to the Yellow Fever Outbreak Toolbox

Key reference documents

Yellow fever fact sheet (Geneva: World Health Organization).
Yellow fever information page (Geneva: World Health Organization).
Yellow fever health topic page (Brazzaville: World Health Organization).
Yellow fever (Washington (DC): Pan American Health Organization; 2019).

Case definitions

WHO suggested outbreak case definition¹

Suspected case:

Any person with acute onset of fever, with jaundice appearing within 14 days of onset of the first symptoms.

Confirmed case:

1. A probable case; and
Absence of yellow fever immunization within 30 days before onset of illness; and one of the following:

detection of yellow fever-specific IgM;² or
detection of fourfold increase in yellow fever IgM, or IgG antibody titres between acute and convalescent serum samples, or both; or
detection of yellow fever-specific neutralizing antibodies.

2. Absence of yellow fever immunization within 14 days before onset of illness; and one of the following:

detection of yellow fever virus genome in blood or other organs by polymerase chain reaction (PCR); or
detection of yellow fever antigen in blood, liver or other organs by immunoassay; or
isolation of yellow fever virus.

WHO surveillance case definition³

Yellow Fever: Vaccine Preventable Diseases Surveillance Standards (Geneva: World Health Organization; 2020).

WHO other definitions

Outbreak definitions:

Presence of at least one confirmed case of yellow fever, as interpreted in a context of underlying population immunity and risk of onward amplification.

_{1. Yellow Fever: Vaccine Preventable Diseases Surveillance Standards (Geneva: World Health Organization; 2020)}

_{2. Yellow fever-specific means that the results of antibody tests (such as IgM or neutralizing antibody) for other prevalent flavivirues are negative or not significant. Testing should include at least IgM for dengue fever and West Nile but may include other flaviviruses according to local epidemiology (for example, Zika virus).}

_{3. Yellow fever confirmation is complex:}

_{Any case classification should account for vaccination status.}
_{Serological testing cannot distinguish between vaccine- and naturally-acquired antibodies.}
_{Yellow fever diagnostic is both positive and differential. It is essential to rule out cross-reactivity with other arboviruses such as dengue, zika, chikungunya or West Nile virus This cross-reactivity can be seen on serology testing (IgM) as well as plague reduction neutralization assays (PRNT).}
_{Results should be interpreted considering local epidemiology of other flaviviruses.}

Data collection tools

Case investigation form(s):
- Form 1 : PDF | Word
- Form 2 : PDF | Word
Line list(s): Not available.
Electronic tools:
- Go. Data yellow fever outbreak template: To download the template and use, kindly email the Go.Data team at godata@who.int