On 6 March 2022, the World Health Organization received notification from the Uganda Ministry of Health of four suspected yellow fever cases, according to a press release. As of 25 April 2022, a total of seven suspected cases tested positive for yellow fever antibodies by plaque reduction neutralization test. However, further investigations identified only one laboratory confirmed case of yellow fever reported from Wakiso district, Central Region. The Ministry of Health declared an outbreak, and a rapid response team was deployed to the affected districts. Due to the potential of epidemic spread in Uganda and the risk of spread to neighboring countries, the World Health Organization assesses the risk to be high at the national and regional levels.
Cases presented with symptoms including fever, vomiting, nausea, diarrhoea, intense fatigue, anorexia, abdominal pain, chest pain, muscle pain, headache, and sore throat. None of the cases presented with severe yellow fever symptoms of acute jaundice. Six of the seven cases were female.
Yellow Fever is a Flavivirus (the group of RNA Viruses that also includes the West Nile, Zika and Hepatitis C Viruses) transmitted to humans by the bites of infected Aedes and Haemagogus Mosquitoes.. The Virus causes a mild fever, accompanied loss of apatite, nausea and muscle pains, which passes within about 15 days. However, in about 15 % of cases a more severe infection attacks the liver and kidneys, which can lead to their failure, and therefore the death of the patient. It originated in tropical Africa and but was carried to South America and the Caribbean during the trans-Atlantic slave trade. Outbreaks of the disease have also been recorded in parts of tropical Asia and the Pacific in recent years, and many countries in tropical regions require visitors to carry a certificate proving they have been vaccinated against the Virus.
Forty countries globally, 27 in Africa and 13 in Central and South America are classified as high-risk for yellow fever. Since September 2021, 13 countries in the World Health Organization African Region have reported probable and confirmed yellow fever cases and outbreaks, including an ongoing outbreak under close investigation in neighbouring Kenya. These outbreaks are occurring in large geographic areas of the Western, Central and Eastern regions of Africa. They have affected areas that have previously conducted large-scale mass vaccination campaigns but with persistent and growing gaps in immunity due to lack of sustained population immunity through routine immunization and/or secondary to population movements (newcomers without history of vaccination). These reports indicate a resurgence and intensified transmission of the yellow fever virus.
After the Uganda Ministry of Health declared a yellow fever outbreak in the country they activated the Public Health Emergency Operation center. They are also deploying a rapid response team to affected districts where all cases were reported to determine the extent of the outbreak, identify the at-risk population, conduct a risk assessment, initiate risk communication and community engagement activities and implement integrated vector control measures.
Yellow fever vaccine has not been introduced into the Uganda routine immunization schedule; however, the country has an imminent plan to introduce it in mid-2022, followed by phased mass vaccination campaigns. Pending the evolution of the situation and response planning, a request maybe submitted to the International Coordinating Group on Vaccine Provision for preventive yellow fever vaccination in areas as indicated by ongoing investigations.
Uganda is endemic for yellow fever and is classified as a high-risk country in the Eliminate Yellow Fever Epidemics (EYE) Strategy. The country has history of outbreaks reported in 2020 (Buliisa, Maracha and Moyo districts), 2019 (Masaka and Koboko districts), 2016 (Masaka, Rukungiri, and Kalangala districts) and in 2010 when ten districts were affected in Northern Uganda.
The confirmed case is reported from Wakiso District, close to the greater Kampala metropolitan area. The district also includes Entebbe, where the international airport is located.
Uganda has not introduced the yellow fever vaccine into routine immunization and the estimated overall population immunity is low (4.2%), and attributable to past reactive vaccination activities supported by International Coordinating Group in focal districts including Yumbe, Moyo, Buliisa, Maracha, Koboko, Masaka, and Koboko, in limited scope in the Greater Kampala area, Masaka, Rukungiri, and Kalangala districts.
Epidemic spread of yellow fever is a risk in Uganda as there could be onward amplification if the virus is introduced in crowded urban areas that are known hubs for travel. There is the risk for further amplification and international spread because of frequent population movements (e.g., between Uganda, Democratic Republic of Congo and South Sudan), coupled with the low population immunity in some neighbouring countries.
The recurrent outbreaks indicate the ongoing risk of zoonotic spill over of yellow fever and risk for disease amplification in both rural and densely settled urban areas in the largely unimmunized population. Despite the yellow fever vaccine being highly effective (99% effective within 30 days of vaccination), the risk of breakthrough cases exists. These cases should be investigated to identify and address possible causes of vaccine failure.
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