Yellow fever

Overview

Yellow fever (YF) is a mosquito-borne acute viral haemorrhagic disease which is caused by the yellow fever virus.

Pathogen(s)

Yellow fever virus (Flavivirus genus, Flaviviridae family)

Transmission

YF is transmitted through the bite of an infected Aedes mosquito. Although there are no reported cases of yellow fever in Singapore, importation of the disease could result in the disease spreading here due to the presence of the Aedes mosquito vector.

Incubation period: 3 to 6 days

Infectious period: Shortly before onset of fever and up to 5 days after onset (when the patient is viraemic).

Clinical features

The majority of the infected persons are asymptomatic or have only mild illness.

Clinical signs and symptoms of yellow fever include fever, headache, myalgia, nausea and vomiting.

A more severe form is characterised by high fever, jaundice, bleeding, and eventually shock and failure of multiple organs.

Risk factors

Travel to a YF endemic area without YF vaccination at least 10 days prior to start of travel.

Diagnosis

YF infection is diagnosed by:

• Viral isolation from blood or tissue specimens

• Identification of viral antigen or nucleic acid in tissues (including liver) using immunohistochemistry (IHC), enzyme-linked immunosorbent. assay (ELISA) antigen capture, or polymerase chain reaction tests

• Serological diagnosis by IgM antibody capture (ELISA), histo- immunochemistry or complement fixation tests (CFT)

Treatment and management

There is no specific treatment for YF. Treatment is mainly supportive.

Precaution, prevention, and control

YF Vaccination

Vaccination is a key preventive measure against YF. To protect persons against YF during travel to countries at risk of YF transmission, it is advised to receive YF vaccination 10 days before travel. A single dose provides life-long protection against YF.

Precautions Against Mosquito Bites

Persons who are ineligible to receive the vaccination (e.g. children aged 1 year and below and persons with contraindications) are advised to take precautions. These include:

• Staying in rooms which are well-screened or air-conditioned

• Wearing long, covered clothing that cover most of the body

• Applying an effective insect repellent, such as those containing DEET, Picaridin or IR3535 as the active ingredient regularly

YF Vaccination Requirements to Enter Singapore

Singapore is free from YF. To reduce the risk of importation and transmission of YF in Singapore, all travellers, including Singapore residents, with travel history to countries with risk of YF transmission (regardless of area, city or region) in the 6 days prior to arrival in Singapore are required to have a valid YF vaccination certificate and present it to the Immigration and Checkpoints Authority (ICA) officer at the immigration counter upon arrival to Singapore. The certificate is also required for travellers with more than 12 hours airport transit in these countries.

The International Certificate of Vaccination for YF becomes valid 10 days after vaccination* and the validity lasts for the life of the person vaccinated.
*e.g., if the YF vaccine was administered on 1 January 2021, the vaccination certificate is considered valid from 11 January 2021 onwards.

Travellers without a valid YF vaccination certificate (e.g., unvaccinated persons, including those who are ineligible to receive the vaccination, and travellers whose certificate has yet to become valid), are liable to be quarantined under the Infectious Disease Act, for 6 days from date of departure from countries with risk of YF transmission. The period of quarantine is to cover the incubation period for YF (i.e., 6 days). For travellers whose vaccination certificate has yet to become valid upon arrival in Singapore, they will still be required to complete the quarantine even if the vaccination certificate subsequently becomes valid during quarantine. This is because they would not have been fully protected against YF during their time in affected countries and may already be infected and incubating the infection. Quarantine must be served at a designated vector-free government quarantine facility. Non-residents who refuse quarantine will be denied entry into Singapore. 

Notification

Who should notify:

• Medical practitioners

• Laboratories

When to notify:

• On clinical suspicion or laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information.

Notification timeline:

• Immediately. No later than 24 hours from the time of diagnosis.