International travel and health

Yellow fever risk mapping and recommended vaccination for travellers

The scientific and technical advisory group on geographical yellow fever risk mapping (GRYF)

Scope of work and functions

WHO recommends Yellow Fever vaccination with three objectives:

  • to review factors important for the transmission of yellow fever virus and country specific yellow fever information;
  • to establish criteria for additions to or removal from the list of countries with risk for yellow fever virus transmission;
  • to prevent international spread by minimizing the risk of introduction or re-introduction of the virus by viraemic travellers1, 2.

The work of the GRYF focuses on the last two objectives related to travel health while the Yellow Fever Initiative works to secure global vaccine supply and boost population immunity by vaccinating people at high risk.

Protection of travellers visiting areas with risk of Yellow Fever

Vaccine should be offered to all unvaccinated travellers aged ≥ 9 months, travelling to and from at-risk areas (Table 1), unless they belong to the group of individuals for whom YF vaccination is contraindicated. In addition for travellers going to areas with low risk of YF transmission, although the vaccination is generally not recommended , it might be considered for the ones travelling for a long period to areas where they may be exposed to heavy load of mosquito bites.

Protection of vulnerable countries

Countries where the vectors and non-human primate hosts exist are vulnerable to the introduction or re-introduction of YF virus, even if the disease is not endemic. Importation of the virus by an infected traveller could initiate an enzootic transmission cycle, leading to a long-term infection risk for the local population. To prevent importation of YF virus, States may decide to require a proof of YF vaccination as a condition of entry to travellers coming from areas with risk of YF transmission.


The GRYF is a formal scientific and technical advisory group3 on geographical yellow fever risk mapping, with the participation of countries with areas with risk of yellow fever, to:

    • maintain up-to-date yellow fever risk mapping; and
    • provide guidance on yellow fever vaccination for travellers in ways that facilitate international travel4 .

In order to achieve the above mentioned objectives, the GRYF will advise the IHR Secretariat on:

  • The definition of criteria for inclusion/exclusion of countries/areas with risk of yellow fever transmission;
  • The review of requests received from Members States including public health justification and scientific data to add or remove countries/areas with risk of yellow fever;
  • Collection, reviewing and analysing new epidemiological data on yellow fever transmission;
  • Proposals for revision of the list of countries /areas with risk of yellow fever transmission;
  • Proposal for revision of the Yellow Fever risk mapping;
  • Promoting the international harmonization of the Yellow Fever risk mapping;
  • Establishment and maintenance of a centralized updated yellow fever country database with the aim of tracking history of risk mapping status changes per country (decision making, rationale, data).

1 WHO position paper, vaccines and vaccination against yellow fever WHO Position Paper – June 2013,
2 Updated list of YF vaccines position paper and all key references with summary,
3 Basic texts, Regulations for Study and Scientific Groups, collaborating institutions and other mechanisms of collaboration ,
4 See resolution WHA68.4 on Yellow fever risk mapping and recommended vaccination for travellers, available at