Yellow fever is an arbovirus closely-related to West Nile, Japanese Encephalitis and St. Louis viruses [1].  Roughly half of those infected are asymptomatic with the remainder [2] ranging from mild disease to fever with jaundice and/or haemorrhage with a 30-60% mortality rate [3].  There is a live-virus vaccine available to humans that are more than nine months old.  It is a highly efficacious, immunogenic vaccine – conferring life-long protective immunity for around 80% and effective immunity for 99% of vaccinated individuals [4, 5].  The virus has three distinct transmission cycles: sylvatic (transmitted to forest workers), intermediate (in savannah regions where humans inhabit jungle borders) and urban (usually introduced by a viremic individual infected in sylvatic or intermediate cycles).  There are different vectors for each of the transmission cycles - Aedes aegypti (urban cycle), Haemagogus sp. (sylvatic), other Aedes spp. (intermediate) [1, 6, 7].  The sylvatic cycle acts as a reservoir of disease.  Mosquitoes primarily acquire the virus on infected primates but, within the urban cycle, the virus is transmitted between susceptible humans.  Patients are viremic (and infectious to mosquitoes) before the onset of fever and 5 days after onset [7].


  1. Hamlet A, Jean K, Perea W, Yactayo S, Biey J, Van Kerkhove M, Ferguson N, Garske T. The seasonal influence of climate and environment on yellow fever transmission across Africa. PLoS neglected tropical diseases. 2018 Mar 15;12(3):e0006284.

  2. Garske T, Van Kerkhove MD, Yactayo S, Ronveaux O, Lewis RF, Staples JE, Perea W, Ferguson NM, Yellow Fever Expert Committee. Yellow fever in Africa: estimating the burden of disease and impact of mass vaccination from outbreak and serological data. PLoS medicine. 2014 May 6;11(5):e1001638.

  3. Johansson MA, Vasconcelos PF, Staples JE. The whole iceberg: estimating the incidence of yellow fever virus infection from the number of severe cases. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2014 Jun 30;108(8):482-7.

  4. Centers for Disease Control and Prevention. Yellow Fever Vaccine. 2019. Available at

  5. Gotuzzo E, Yactayo S, Córdova E. Efficacy and duration of immunity after yellow fever vaccination: systematic review on the need for a booster every 10 years. The American journal of tropical medicine and hygiene. 2013 Sep 4;89(3):434-44.

  6. Barrett AD, Higgs S. Yellow fever: a disease that has yet to be conquered. Annu. Rev. Entomol.. 2007 Jan 7;52:209-29.

  7. Monath TP, Vasconcelos PF. Yellow fever. Journal of clinical virology. 2015 Mar 1;64:160-73.