Yellow Fever: Understanding the disease and vaccine hesitancy

26 August 2024, 1:02 pm

By Byamukama Alozious

Yellow fever is a viral haemorrhagic disease that has affected humans for centuries, with its origins traced back to Africa around 3,000 years ago. The disease, transmitted primarily by Aedes aegypti mosquitoes, remains a significant public health concern in many parts of the world, particularly in Africa and South America. Although a highly effective vaccine has been available for over 80 years, recent outbreaks have highlighted persistent challenges, including vaccine hesitancy driven by mistrust and misconceptions.

According to the World Health Organisation, 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 a history of outbreaks reported in 2020 (Buliisa, Maracha, and Moyo districts), 2019 (Masaka and Koboko districts), 2016 (Masaka, Rukungiri, and Kalangala districts), and 2010, when ten districts in Northern Uganda were affected.

The Ugandan government has intensified efforts to address yellow fever through targeted vaccination campaigns and by incorporating the yellow fever vaccine into routine immunisation for children. These campaigns, supported by international partners, have been conducted in high-risk districts such as Yumbe, Moyo, and Buliisa, aiming to bolster immunity and prevent further outbreaks.

Additionally, yellow fever vaccination has become a standard part of routine immunisation for infants, ensuring early protection against the disease. Uganda has also implemented a policy requiring a yellow fever vaccination card for both domestic and international travel, reinforcing the importance of vaccination and helping to control the spread of the disease.

Yellow fever likely originated in Africa, where it was transmitted from non-human primates to humans via mosquitoes. The disease spread to the Americas and other parts of the world through the transatlantic slave trade and increased global trade and travel. By the 17th and 18th centuries, yellow fever had become a formidable epidemic threat in port cities across the Americas, causing significant mortality and economic disruption.

Yellow fever is characterised by its two-phase clinical progression. The acute phase, which appears 3-6 days after infection, includes symptoms such as fever, chills, headache, back pain, loss of appetite, nausea, and vomiting. Most patients recover within a week.

About 15% of those initially infected progress to the toxic phase, which can be life-threatening, with symptoms including high fever, jaundice (hence the name “yellow” fever), bleeding, and organ failure. The toxic phase can result in death for 20-50% of patients without medical intervention.

The disease is endemic to 34 African and 13 South American countries. Although Asia has the potential for outbreaks due to the presence of suitable mosquito vectors, no yellow fever cases have been recorded there. The distribution of the disease and periodic outbreaks underscore the importance of vaccination, especially in endemic regions.

Despite advances in medical science, several misconceptions about yellow fever persist. Many people believe that yellow fever is transmitted only by mosquitoes, though it can also be transmitted through contact with infected blood or bodily fluids, albeit rarely.

Another misconception is that yellow fever is exclusively an African problem, while it is also present in South America. Additionally, some believe that yellow fever is no longer a serious threat, although the disease remains severe, with those who enter the toxic phase facing a high risk of complications and death.

The live attenuated yellow fever vaccine, developed over 80 years ago, has proven highly effective. A single dose can elicit a robust immune response, with 94% of recipients showing neutralising antibodies three months post-vaccination.

For most individuals, this immunity is long-lasting, eliminating the need for booster doses in non-endemic regions. Recent research, including a meta-analysis published in The Lancet Global Health, has found high long-term immunity in non-endemic regions, with 94% of individuals retaining protective antibody levels 10 to 60 years post-vaccination.

However, in endemic areas like Brazil, seroprotection rates dropped to 76%, suggesting potential waning immunity over time. Vulnerable populations, such as children under two and individuals with HIV, exhibited lower immunity, indicating a need for booster doses.

The study highlighted a lack of high-quality research from sub-saharan Africa and other endemic regions, complicating efforts to assess the vaccine’s long-term efficacy in these areas. Additionally, logistical challenges, misinformation, and vaccine hesitancy pose significant barriers to vaccination efforts.

Root causes of hesitancy include mistrust in authorities, cultural beliefs, and perceived low risk. Vaccine hesitancy can have severe consequences, including an increased risk of outbreaks and strain on healthcare systems.

Efforts to combat vaccine hesitancy must include community engagement, educational campaigns, and improved access to vaccines. Misinformation and cultural beliefs need to be addressed to build trust and ensure widespread vaccine coverage. By implementing these strategies, the impact of yellow fever can be significantly reduced, protecting vulnerable populations worldwide.