Yellow Fever: Still circulating in a vaccine Era, capturing The Americas and Africa, Cameroon in the Spotlight

Yellow Fever Immunization: Where We Stand in 2025

Despite 85 years of a highly effective and safe yellow fever vaccine, yellow fever continues to circulate in endemic regions. Routine immunization still covers only about half of the world’s population living in risk areas—roughly 50 percent in 2023—far below the 95 percent threshold needed for herd immunity. In the same year, regional performance remains uneven: coverage in the African Region averaged 48 percent, while the Region of the Americas reached 63 percent.

A handful of countries are closing the gap. In Africa, Rwanda stands at 99 percent and Ghana at 88 percent. In the Americas, Ecuador and Guyana have surpassed 95 percent, and Suriname at 91 percent, and Trinidad and Tobago at 90 percent.

At the same time, climate change, rapid urbanization, land-use shifts and increased global travel are expanding Aedes mosquito habitats, allowing the virus to infiltrate previously unaffected areas and challenging decades of control effort.

Yellow Fever in 2025: A Global Snapshot

The sharpest resurgence this year is unfolding in the Americas. As of April 26, 2025, five countries—Bolivia, Brazil, Colombia, Ecuador, and Peru—reported 212 confirmed infections and 85 deaths, marking a steep rise from the 61 cases and 30 deaths recorded in 2024. Last year, transmission was concentrated in Bolivia, Colombia, Guyana, and Peru, but in 2025, yellow fever has expanded into new areas. Cases are spilling beyond the traditional Amazon basin and appearing in areas like São Paulo State in Brazil and Tolima Department in Colombia, raising serious concerns about potential urban transmission cycles.

This geographic expansion beyond historical transmission zones has prompted health authorities to reinforce travel recommendations. Any traveler heading to areas where yellow fever circulates should receive a single lifetime dose of vaccine before departure, as the virus's reach continues to broaden unpredictably.

Africa’s uneasy equilibrium

Yellow fever transmission has never ceased in Africa, but its patterns are evolving in concerning ways. Between January 2023 and February 2024, probable or confirmed yellow fever cases were recorded in 13 countries, including Burkina Faso, Cameroon, Central African Republic, Chad, Republic of the Congo, Côte d'Ivoire, Democratic Republic of the Congo, Guinea, Niger, Nigeria, South Sudan, Togo, and Uganda. While most outbreaks were contained swiftly, persistent structural challenges continue to allow transmission to simmer beneath the surface.

Provisional 2024 data show at least 124 laboratory-confirmed yellow-fever cases in 12 African countries, with eight deaths— a case-fatality rate of roughly 6 percent and more than double the pre-pandemic average case count. By contrast, 2023 recorded about 60 confirmed cases but a far higher fatality ratio of 11 percent, highlighting how quickly infections can turn lethal when detection and care are delayed. Despite ongoing efforts to maintain routine immunization programs, subnational gaps in vaccine coverage, population displacement, and limited surveillance capacity allow small clusters of infection to persist undetected, creating reservoirs for future outbreaks.

Routine programs struggle to reach the last 20% of children, especially where conflict, displacement and weak laboratory networks hamper service delivery. Surveillance remains the continent's weakest link in yellow fever control. Fragmented data systems, delayed laboratory confirmation, and chronic underreporting all contribute to silent transmission, making it extremely difficult to track the virus's true geographic spread. While emergency vaccination campaigns have successfully contained declared outbreaks, conflict-affected areas and regions with high population mobility remain vulnerable to sudden resurgence.

The urgency of addressing these surveillance and immunization gaps cannot be overstated. Strengthening routine vaccination coverage, expanding laboratory diagnostic capacity, and accelerating outbreak response times will be essential to shifting yellow fever's trajectory across the African continent.

Cameroon in the spotlight

Cameroon exemplifies both the challenges and opportunities facing yellow fever control in Africa. From epidemiological week 1 to week 49 of 2024, health teams investigated 2,224 suspected yellow fever infections nationwide. Six cases were ultimately confirmed through laboratory testing, with one proving fatal, yielding a case-fatality ratio of 16.7%. The most recent confirmed case had symptom onset on 11 August 2024, while nine additional plaque-reduction neutralization test positive samples await final classification under WHO case-definition criteria.

Laboratory surveillance in 2024 revealed the complexity of yellow fever diagnosis in a region where multiple flaviviruses circulate. Health teams identified 76 IgM-positive samples indicating recent flavivirus infection, though these results may cross-react with dengue or Zika viruses. More specifically, 28 samples tested positive for yellow fever neutralizing antibodies through specialized testing, with six meeting the strict criteria for confirmed yellow fever cases through both laboratory and clinical validation.

Cameroon recorded 45 laboratory-confirmed yellow fever cases in 2021, 41 in 2022 with 9 deaths, 35 in 2023 with 5 deaths, and 6 confirmed cases in 2024 with 1 death, totaling 127 laboratory-confirmed infections and 15 deaths over the four-year period. While the confirmed case count declined sharply in 2024, with additional cases still under laboratory review, surveillance continues to identify thousands of suspected cases. Currently, 26 of the country's 200 health districts remain classified as epidemic-prone, many located along busy trade corridors where human movement and Aedes mosquito populations converge. Enhanced PCR diagnostic capacity and faster PRNT testing represent encouraging improvements in surveillance capabilities, but expanding routine immunization coverage remains critical to closing protection gaps and preventing transmission resurgence in these high-risk districts.

 Why infections persist

Despite ongoing vaccination efforts, yellow fever continues to emerge in Cameroon due to several interconnected challenges that mirror broader regional patterns. Immunity gaps remain a fundamental concern. In 2024, the yellow fever vaccination coverage was 80%, the highest coverage attained since the yellow fever vaccine introduction in 2004, this still leaves substantial pockets of unprotected children and adults vulnerable to infection when the virus circulates.

Rapid urban expansion in major cities like Douala and Yaoundé has created densely populated neighborhoods with abundant breeding sites for Aedes aegypti mosquitoes, significantly increasing transmission risk when infected individuals arrive from endemic forest areas. Climate pressures are simultaneously shifting traditional transmission patterns, as higher temperatures extend mosquito survival periods and make seasonal outbreak timing less predictable for public health planners.

Population movement further complicates control efforts across the region. Conflict-driven displacement and regular cross-border trade frequently disrupt vaccination campaigns, making it extremely difficult to reach and protect high-risk mobile populations. Additionally, surveillance bottlenecks consistently slow response times, with sample transport to reference laboratories and confirmatory testing often requiring more than a week, delaying critical ring vaccination efforts and allowing localized outbreaks to expand before effective containment measures can be implemented.

Strengthening yellow fever control

Cameroon's Ministry of Public Health has made important strides by integrating yellow fever vaccination with the routine 9-month measles–rubella immunization visit (free of charge), ensuring early protection for infants during a critical vulnerability window. When cases emerge, health authorities deploy ring vaccination strategies in affected areas to create protective barriers around outbreak sites and prevent further geographic spread.

To reinforce Cameroon's response capacity and sustain recent progress, three critical interventions require immediate attention and sustained political commitment. First, detailed micro-planning must be completed before the upcoming rainy season begins. Trained surge teams, drawing expertise from successful malaria and polio eradication programs, should systematically update household registers in high-risk areas, enabling health workers to locate and immunize every previously missed child and adult before peak mosquito breeding season amplifies transmission risk.

Second, laboratory testing capacity must be substantially expanded to support rapid outbreak detection and response. Equipping at least two strategically located regional laboratories with plaque-reduction neutralization test capabilities will dramatically accelerate case confirmation processes, enabling faster deployment of control measures and more precise targeting of vaccination campaigns based on reliable epidemiological intelligence.

Third, community engagement strategies must be strengthened to increase vaccine acceptance and demand across all demographic groups. A comprehensive "One Shot for Life" communication campaign, designed in plain language and led by trusted community voices including faith leaders, local influencers, and respected healthcare advocates, should utilize social media, television, and radio platforms to dispel persistent vaccine misconceptions and actively encourage parents and adults to seek immunization at accessible vaccination sites. As adult immunization is not available for free, ensuring accessible vaccine cost by reducing the current price by at least 60% is critical—currently, one dose of the adult yellow fever vaccine can cost up to 15,000 FCFA (~$26 USD), creating a significant barrier to uptake among vulnerable populations.

Clear, culturally appropriate messaging will prove essential to reducing vaccine hesitancy and expanding population-level coverage to protective thresholds. With these evidence-based measures implemented systematically, Cameroon can significantly improve disease surveillance sensitivity, enhance vaccination outreach effectiveness, and strengthen public health awareness, ensuring that yellow fever outbreaks remain contained and ultimately prevented.

The bottom line

Yellow fever's continued circulation is not a failure of medical science or vaccine technology. The yellow fever vaccine remains highly effective with excellent safety profiles, and global vaccine stocks are currently adequate to meet demand. The real challenge facing endemic countries is fundamentally operational: reaching every vulnerable person with vaccination before mosquitoes can complete transmission cycles, maintaining rapid surveillance systems that detect cases quickly, and sustaining high-level political commitment to prevention programs even after media attention fades and competing health priorities emerge.

The decisions taken now regarding vaccination strategy implementation, integrated vector control programs, and early warning system strengthening will ultimately determine whether 2025 becomes the year that Cameroon and the broader West and Central African region successfully push yellow fever back toward historical irrelevance, or whether current gains are lost to renewed circulation and preventable outbreaks.

Subscribe to my weekly updates on global health challenges, humanitarian crises, and evidence-based strategies for creating lasting public health impact.

Tambe Elvis Akem Medical Field Epidemiologist | Health & Immunization Specialist | Advocate for Equity in Health

@ImmunizationForResilienceNewsletter

"In the midst of every crisis lies great opportunity—not just to rebuild, but to reimagine."