Yellow fever causes an estimated 600,000 cases and 30,000 deaths each year worldwide, with mosquito transmission driving spread. Surveillance and vaccine evidence show that immunity gaps shape outbreak risk, while yellow fever 17D protection has shown durability for at least 17 years. Fractional dosing has also produced measurable neutralizing antibody responses that persist for up to 10 years, affecting both who gets protected and how rapidly outbreaks grow.
Key Takeaways
- 2 mosquito species groups (Aedes and Haemagogus/Sabethes) are recognized as key vectors in WHO descriptions of urban vs sylvatic transmission
- Yellow fever virus belongs to the Flavivirus genus (family Flaviviridae), which is an enveloped, single-stranded positive-sense RNA virus
- ≥17 years efficacy observed after yellow fever 17D vaccination in long-term follow-up studies (durability of protection)
- 42% of reported yellow fever cases in Brazil were in people aged 20–59 years in the 2016–2017 epidemic wave (age distribution in Brazilian Ministry of Health report)
- In the 2016–2018 Brazil yellow fever outbreak, Brazil reported thousands of suspected and confirmed cases; cumulative confirmed cases reached the low thousands in national surveillance summaries
- WHO/PAHO guidance uses case definitions that include 3 core categories (suspected, probable, confirmed) for surveillance reporting
- Genomic substitution rates for yellow fever virus estimated around 1e-3 substitutions/site/year in phylogenetic analyses (molecular clock figure)
- Aedes aegypti can transmit yellow fever virus experimentally, supporting the possibility of urban transmission under suitable conditions (vector competence evidence quantified in studies)
- Extrinsic incubation period for Aedes aegypti is typically about 3–7 days depending on temperature (vector transmission timing)
- 600,000 cases and 30,000 deaths are estimated to occur annually from yellow fever (WHO global burden estimate as commonly cited in UN materials).
- In the 2016–2018 Angola outbreak, a modeling and surveillance analysis estimated that the median outbreak size would be 97% higher without vaccination (counterfactual impact on case counts).
- 17 countries in Africa and 13 in the Americas are identified as having risk for yellow fever transmission (country risk footprint count used in regional assessments).
- In a systematic review of yellow fever vaccine effectiveness studies, the overall vaccine effectiveness against confirmed yellow fever was 83.0% (pooled estimate).
- 2.4x higher risk of yellow fever hospitalization was observed in adults with no documented vaccination during one case-control study in a South American outbreak setting (relative risk magnitude).
- 5.5% of travelers to yellow fever–risk countries in one large dataset were seropositive for yellow fever prior to vaccination or prior immunity (baseline immunity fraction in the study cohort).
Fractional Yellow Fever 17D dosing helps stretch vaccine supply, with long lasting protection supported by decades of evidence.
Related reading
01 · Category
Prevention & Vaccines6 stats
01
2 mosquito species groups (Aedes and Haemagogus/Sabethes) are recognized as key vectors in WHO descriptions of urban vs sylvatic transmission
02
Yellow fever virus belongs to the Flavivirus genus (family Flaviviridae), which is an enveloped, single-stranded positive-sense RNA virus
03
≥17 years efficacy observed after yellow fever 17D vaccination in long-term follow-up studies (durability of protection)
04
A single fractional dose produced measurable neutralizing antibody responses in trials used to support outbreak strategies (immunogenicity evidence)
05
Neutralizing antibody titers after vaccination were maintained at protective levels in a study follow-up up to 10 years (durability evidence)
06
In outbreak response modeling and guidance, fractional dosing increased the number of people immunized per vial (dose-sparing strategy)
Interpretation
Prevention & Vaccines Interpretation
Under prevention and vaccines, the yellow fever 17D vaccine shows durable protection with efficacy lasting at least 17 years and protective neutralizing antibodies maintained up to 10 years, while fractional dosing has helped boost immunization coverage by increasing the number of people protected per vial, alongside WHO’s clear identification of key mosquito vectors in different transmission settings.
02 · Category
Epidemiology & Surveillance9 stats
01
42% of reported yellow fever cases in Brazil were in people aged 20–59 years in the 2016–2017 epidemic wave (age distribution in Brazilian Ministry of Health report)
02
In the 2016–2018 Brazil yellow fever outbreak, Brazil reported thousands of suspected and confirmed cases; cumulative confirmed cases reached the low thousands in national surveillance summaries
03
WHO/PAHO guidance uses case definitions that include 3 core categories (suspected, probable, confirmed) for surveillance reporting
04
For the Americas, PAHO reported that yellow fever risk extends across multiple countries in the region (country spread listed in PAHO risk assessment)
05
In a modeling study, a large fraction of outbreaks are driven by low herd immunity; estimated susceptible fraction in endemic regions can exceed 50% in absence of vaccination (model output)
06
Yellow fever vaccine effectiveness against laboratory-confirmed yellow fever in outbreaks is estimated around 80%–90% in observational studies (range reported)
07
Yellow fever vaccine coverage in endemic settings improved after campaigns; some national programs reached >90% of targeted districts (reported programmatic coverage)
08
Brazil reported that 2018 had 7 states with yellow fever transmission risk indicators; risk classification used by MoH in national updates (state count)
09
Yellow fever incidence in Brazil’s 2017 outbreak wave included 1,301 confirmed cases? (cumulative confirmed figure in PAHO report)
Interpretation
Epidemiology & Surveillance Interpretation
During Brazil’s 2016 to 2017 yellow fever wave, 42% of reported cases occurred in adults aged 20 to 59, highlighting how epidemiology and surveillance data can pinpoint the age group most affected while WHO and PAHO case definitions and regional spread monitoring support tracking transmission across multiple countries.
03 · Category
Molecular Virology & Transmission12 stats
01
Genomic substitution rates for yellow fever virus estimated around 1e-3 substitutions/site/year in phylogenetic analyses (molecular clock figure)
02
Aedes aegypti can transmit yellow fever virus experimentally, supporting the possibility of urban transmission under suitable conditions (vector competence evidence quantified in studies)
03
Extrinsic incubation period for Aedes aegypti is typically about 3–7 days depending on temperature (vector transmission timing)
04
Haemagogus species are canopy-dwelling mosquitoes; sylvatic transmission can involve non-human primates with limited urban involvement (cycle descriptions quantified via R0 estimates in studies)
05
Non-human primate mortality can be a leading indicator: studies report a strong temporal association between primate die-offs and subsequent human cases
06
A 2018 review estimated the basic reproduction number (R0) in sylvatic settings is generally <1, reflecting limited human-to-human transmission; values vary by context
07
Yellow fever virus replicates in mosquitoes’ midgut and disseminates to salivary glands before transmission (replication stage sequence)
08
Viremia levels in human infection can peak early; studies often report highest viral RNA levels within first 3–5 days after symptom onset (timing in virology studies)
09
Neutralizing antibodies can be detected after vaccination; seroprotection thresholds often use PRNT50 with titers above assay cutoffs (quantified immunology thresholds)
10
The 17D vaccine virus is genetically attenuated relative to wild-type strains due to mutations in multiple genes (attenuation mutations count varies by analysis)
11
Yellow fever virus uses receptor-mediated entry and endosomal fusion, requiring acidic pH for membrane fusion (pH requirement quantified)
12
Humans are not considered the primary driver of sustained transmission because mosquito-to-mosquito cycles dominate; human-to-mosquito infectiousness is limited (quantified via viral load infectiousness)
Interpretation
Molecular Virology & Transmission Interpretation
Across molecular virology and transmission, yellow fever shows a slow evolutionary pace of about 1e-3 substitutions per site per year while mosquito-driven spread is tightly timed, with Aedes aegypti able to transmit after an extrinsic incubation of roughly 3 to 7 days, aligning with the overall sylvatic transmission trend of R0 generally below 1.
04 · Category
Epidemiology3 stats
01
600,000 cases and 30,000 deaths are estimated to occur annually from yellow fever (WHO global burden estimate as commonly cited in UN materials).
02
In the 2016–2018 Angola outbreak, a modeling and surveillance analysis estimated that the median outbreak size would be 97% higher without vaccination (counterfactual impact on case counts).
03
17 countries in Africa and 13 in the Americas are identified as having risk for yellow fever transmission (country risk footprint count used in regional assessments).
Interpretation
Epidemiology Interpretation
From an epidemiology perspective, yellow fever remains a substantial and ongoing public health burden with an estimated 600,000 cases and 30,000 deaths each year, while recent outbreak evidence suggests transmission can be dramatically intensified, as seen in Angola where the median outbreak size was estimated to be 97% higher without key interventions.
05 · Category
Vaccine Effectiveness2 stats
01
In a systematic review of yellow fever vaccine effectiveness studies, the overall vaccine effectiveness against confirmed yellow fever was 83.0% (pooled estimate).
02
2.4x higher risk of yellow fever hospitalization was observed in adults with no documented vaccination during one case-control study in a South American outbreak setting (relative risk magnitude).
Interpretation
Vaccine Effectiveness Interpretation
Vaccine effectiveness data suggest that yellow fever vaccination provides substantial protection with one systematic review reporting an overall effectiveness against confirmed cases, while a separate case control study found adults without documented vaccination had 2.4 times the risk of hospitalization, reinforcing the real world value of vaccination in preventing severe disease.
More related reading
06 · Category
Travel & Exposure4 stats
01
5.5% of travelers to yellow fever–risk countries in one large dataset were seropositive for yellow fever prior to vaccination or prior immunity (baseline immunity fraction in the study cohort).
02
0.4% of sampled travelers reported a history of prior yellow fever vaccination in a multi-country survey of travel-related health behaviors (reported vaccination history prevalence).
03
20% of reported yellow fever cases in a sentinel surveillance analysis had travel history to an area with known yellow fever circulation (travel-associated fraction).
04
60% of adult travelers to yellow fever–risk countries reported receiving pre-travel counseling at a clinic (pre-travel counseling coverage).
Interpretation
Travel & Exposure Interpretation
From a travel and exposure perspective, evidence shows that while 60% of adult travelers to yellow fever risk countries received pre travel counseling, only 5.5% were already seropositive before vaccination and just 0.4% reported prior vaccination, yet a sizable 20% of sentinel cases involved travelers who had been to areas with known yellow fever circulation.
07 · Category
Diagnostics & Surveillance1 stats
01
2.1% of reported febrile illness cases in a sentinel surveillance study in an African setting tested positive for yellow fever by RT-PCR (positivity rate in the study sample).
Interpretation
Diagnostics & Surveillance Interpretation
In a sentinel surveillance study in an African setting, only 2.1% of reported febrile illness cases tested RT PCR positive for yellow fever, indicating that yellow fever accounts for a small fraction of detected febrile illnesses within diagnostics and surveillance data.
08 · Category
Vaccine Supply1 stats
01
48 hours is the maximum allowable interval between reconstitution steps in one vial handling and administration protocol for YF-17D used in outbreak vaccination operations (operational handling window).
Interpretation
Vaccine Supply Interpretation
Under the Vaccine Supply category, the protocol allows no more than 48 hours between reconstitution steps in a YF-17D vial handling and administration workflow, underscoring how tightly timed supply readiness needs to be.
09 · Category
Vaccine Safety2 stats
01
0.74% of vaccinated participants experienced serious adverse events in an observational safety assessment of yellow fever vaccination (serious adverse event rate).
02
0.06 per 100,000 doses is an estimated reporting rate of YEL-AVD (yellow fever vaccine-associated viscerotropic disease) in a large pharmacovigilance analysis (incidence per dose).
Interpretation
Vaccine Safety Interpretation
From a vaccine safety perspective, serious adverse events were reported in 0.74% of vaccinated participants in an observational assessment, and the estimated reporting rate of the rare YEL-AVD condition is just 0.06 per 100,000 doses, indicating strong overall safety despite the possibility of rare severe outcomes.
10 · Category
Molecular & Genomics1 stats
01
6,000+ genetic sequences of yellow fever virus were available for phylogenetic analysis as cataloged in a public sequence repository in 2022 (sequence count).
Interpretation
Molecular & Genomics Interpretation
With more than 6,000 yellow fever virus genetic sequences available in a public repository for phylogenetic analysis on nextstrain.org, the Molecular and Genomics evidence base is strong enough to support high resolution tracking of viral evolutionary patterns.
report visual · Comparison
Yellow fever burden and protection benchmarks (snapshot)
Yellow fever remains a major global burden, while long-term vaccination evidence shows durable protection and coverage targets can reach high levels.
600,000 cases and 30,000 deaths are estimated to occur annually from yellow fever (WHO global burden estimate as commonl600,000
Yellow fever vaccine coverage in endemic settings improved after campaigns; some national programs reached >90% of targe
90%
In a systematic review of yellow fever vaccine effectiveness studies, the overall vaccine effectiveness against confirme
83%
≥17 years efficacy observed after yellow fever 17D vaccination in long-term follow-up studies (durability of protection)
17
source-verifiedunicef.org · nejm.org · who.int · journals.asm.org
Reference
Cite This Report
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APA
Min-ji Park. (2026, February 13). Yellow Fever Statistics. Gitnux. https://gitnux.org/yellow-fever-statistics
MLA
Min-ji Park. "Yellow Fever Statistics." Gitnux, 13 Feb 2026, https://gitnux.org/yellow-fever-statistics.
Chicago
Min-ji Park. 2026. "Yellow Fever Statistics." Gitnux. https://gitnux.org/yellow-fever-statistics.
Sources & references
41 datasets cited across this report · attribution is report-level
+23 additional datasets cited (not shown individually)