Yellow fever (YF) is a viral haemorrhagic fever and is transmitted by mosquitos infected with the YF virus. The disease is untreatable and case-fatality rates can exceed 50% among severe cases. YF can be prevented through immunization with the 17D YF vaccine, which is safe, inexpensive and reliable. A single dose provides lifelong protection against the disease.

A high risk exists of an explosive outbreak in an unimmunized population even if there is only one laboratory-confirmed case in the population. Children are especially vulnerable. Effective disease surveillance activities remain the best tool for prompt detection of and response to outbreaks, particularly in populations where coverage rates for YF vaccine are not high enough to provide protection.

Each country at risk should include YF surveillance in its national priorities for disease surveillance. Current capacity for YF surveillance should be assessed and a plan of action for establishing or strengthening it should be implemented. The minimum requirements for a YF surveillance system are detection, investigation, specimen collection and a reporting system for suspected cases, linked to confirmatory testing of samples.

All countries at risk should have access to a qualified laboratory capable of testing for YF, minimally by an IgM serological test, and ideally through the combination of both RT-qPCR and IgM testing, while ensuring all IgM positive specimens need further confirmatory testing by a specialized lab in the Region. As such, all countries should be aware of the regional reference laboratories that can aid them in confirmatory testing. Procedures for transporting specimens between laboratories and for testing the specimens should be formally established.

The Global Yellow Fever Laboratory Network (GYFLaN) was developed in 2005 based on the successful model of the Global Polio Laboratory Network and the Global Measles and Rubella Laboratory Network. The GYFLaN is an international coalition of laboratories routinely testing for yellow fever (YF) as part of active national YF surveillance programmes in endemic areas of the African and Eastern Mediterranean regions and the region of the Americas. These laboratories individually serve front-line YF diagnostic testing functions for YF surveillance in their respective countries, critical in identifying YF outbreaks.

Working closely together, the GYFLaN laboratories, the country disease surveillance and immunization programmes and their partners, and the Ministries of Health coordinate testing, including confirmatory YF diagnostic testing at the regional level, communication of results, case classification, and strategic/preventive programmatic responses. The efficiency of this process and accuracy of results are paramount considering that a single confirmed YF case can be enough to initiate an outbreak response. The hierarchy of laboratories is represented below, associated with this list of GYFLaN laboratories.

Figure: Structure and function of the GYFLaN

Abbreviations: GSL : Global Specialized Laboratory; RRL: Regional Reference Laboratory; WHO CC: World Health Organization’s Collaborative Centers; NL: National Laboratory; SN: Sub-National Laboratory

As of 2026, the network is composed of 70 laboratories from 59 countries. Working as a coordinated network enables the standardization of practices, validation of novel methods, and capacity building. This strong and resilient global network is the key to regional and national YF detection capacity, even including for countries with fewer suspected cases which can have access to quality testing.

Activities of the GYFLaN

There are three broad areas of activities that GYFLaN laboratories carry out in support of the YF surveillance programmes. These are listed and discussed in detail in the WHO YF Laboratory Manual. Briefly, these are:

• Timely and accurate laboratory testing for YF surveillance and early detection of YF cases to allow rapid implementation of control measures. Primary detection methods are real-time reverse transcription polymerase chain reaction (RT-qPCR) for detection of viral RNA and detection of IgM antibodies to YF. Confirmatory detection of antibodies uses plaque-reduction neutralization test (PRNT).
• Communication and documentation of laboratory results and data at local and national levels. Weekly or monthly reports are provided to WHO.
• Participation in WHO quality assessment and accreditation programmes. Proficiency testing via external quality assessments and annual WHO accreditation are required for GYFLaN laboratories. Quality control is also maintained by comparison of NL test results with those of their designated RRL for a percentage of the samples. More details can be found on the Lab performance monitoring page. 

Coordination

The GYFLaN is coordinated by the World Health Organization (WHO), where the African Region (AFR), the Eastern Mediterranean Region (EMR), and the Region of the Americas (AMR) Regional Coordinators (RC) work closely with the Network laboratories and with the GYFLaN Coordinator at WHO Headquarters (WHO HQ).

Other WHO guidance documents and technical reports related to yellow fever laboratory testing in the context of surveillance include:

Online Technical Resource Library for Yellow Fever Laboratory Testing:

Yellow Fever Laboratory Information Sharing Platform – EYE LABS