Search

Background: Immunization against the Yellow fever virus (YFV) with the 17D live-attenuated vaccine is the most effective way to prevent the disease. However, unexpected severe adverse events can occur. They consist in a neurological impairment - neurological disease (YEL-AND), a YF-like illness - viscerotropic disease (YEL-AVD) or anaphylaxis. In this article, we describe the epidemiology, clinical and biological features of YEL-AND and YEL-AVD cases reported to the French National Reference Center for Arboviruses (NRCA) in the past 10 years., Methods: We conducted a national, retrospective study using the database of the NRCA from June 2012 to June 2022. All patients whose biological samples were sent to the NRCA for detection of YFV by serology and/or RT-qPCR for a suspected vaccine-associated adverse event were included. We collected data by reading medical records and conducted complementary neuro-immunological analysis, followed by a search for autoimmunity against type-1-interferon when samples were available at the NRCA., Results: There were 10 cases of YEL-AND and 2 cases of YEL-AVD reported to the NRCA in the past 10 years, which represented an overall incidence of 0.6 for 100 000 doses. A total of 6/12 cases were previously healthy patients (50%, mean age 31 years), and 4/12 cases had cardiovascular co-morbidities (42%, mean age 56 years). The majority of YEL-AND had a favourable outcome at 6 months of follow up. One YEL-AVD patient passed. In secondary analyses, we evidenced a significant blood cerebrospinal fluid (CSF) barrier dysfunction, without intrathecal synthesis of immunoglobulin and without argument for a neuron damage. We further detected a significant rate of anti-type-1alpha interferon antibodies in 3/10 tested patients (2 YEL-AND and 1 YEL-AVD)., Conclusion: YEL-AND and YEL-AVD are rare events that can underlie defect in the innate immunity of apparently healthy or mild co-morbid subjects. Outcome was generally favourable in the YEL-AND cases of our series, but still life-threatening or even fatal in the YEL-AVD cases., (© International Society of Travel Medicine 2023. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Background: The incidence of anaphylaxis after receipt of yellow fever (YF) vaccine is highly variable based upon previously published reports. Anaphylaxis after receiving the YF vaccine has been reported to range from 0 up to 22 per 1 000 000 doses. Our clinical experience suggested increased incidence, which prompted our investigation. We sought to evaluate the current incidence rate of anaphylaxis after receipt of the 17D-204 strain YF-VAX® brand reported in the US., Methods: We performed a retrospective review of the Vaccine Adverse Event Reporting System (VAERS) reports of anaphylaxis after receiving the YF-VAX vaccine occurring between 1 October 1999 and 30 September 2018. We utilized the Brighton Collaboration Case Definition and inclusion determination was made by a board-certified allergist. We also obtained the total number of YF-VAX doses distributed across the US during this same time-period and then calculated an updated incidence rate of YF-VAX vaccine-associated anaphylaxis., Results: We identified 132 potential cases of possible or probable anaphylaxis. Of these, 111 met inclusion criteria: level 1 (n = 51), level 2 (n = 59) and level 3 (n = 1). The manufacturer reported a total distribution of 7 624 160 doses of YF-VAX from 1 October 1999 to 30 September 2018. The calculated incidence rate of YF-VAX vaccine-associated anaphylaxis is estimated at 14.6 events per 1 000 000 doses., Conclusions: We conclude the estimated rate of anaphylaxis per VAERS reports is 14.6 events per 1 000 000 doses after YF-VAX vaccination. This is consistent with some previous reports and substantially higher than rates of anaphylaxis after other vaccines., (Published by Oxford University Press on behalf of International Society of Travel Medicine 2023.)

Background: There is concern about the risk of yellow fever (YF) establishment in Asia, owing to rising numbers of urban outbreaks in endemic countries and globalisation. Following an outbreak in Angola in 2016, YF cases were introduced into China. Prior to this, YF had never been recorded in Asia, despite climatic suitability and the presence of mosquitoes. An outbreak in Asia could result in widespread fatalities and huge economic impact. Therefore, quantifying the potential risk of YF outbreaks in Asia is a public health priority., Methods: Using international flight data and YF incidence estimates from 2016, we quantified the risk of YF introduction via air travel into Asia. In locations with evidence of a competent mosquito population, the potential for autochthonous YF transmission was estimated using a temperature-dependent model of the reproduction number and a branching process model assuming a negative binomial distribution., Results: In total, 25 cities across Asia were estimated to be at risk of receiving at least one YF viraemic traveller during 2016. At their average temperatures, we estimated the probability of autochthonous transmission to be <50% in all cities, which was primarily due to the limited number of estimated introductions that year., Conclusion: Despite the rise in air travel, we found low support for travel patterns between YF endemic countries and Asia resulting in autochthonous transmission during 2016. This supports the historic absence of YF in Asia and suggests it could be due to a limited number of introductions in previous years. Future increases in travel volumes or YF incidence can increase the number of introductions and the risk of autochthonous transmission. Given the high proportion of asymptomatic or mild infections and the challenges of YF surveillance, our model can be used to estimate the introduction and outbreak risk and can provide useful information to surveillance systems., (© International Society of Travel Medicine 2021. Published by Oxford University Press.)

Rapid increase in trade and a growing air passenger market encourages high travel volume between the regions associated with increasing risks of such importations including China. Eleven Chinese workers infected during the 2016 yellow fever (YF) outbreak in Angola imported YF into China highlighting the potential for spread into Asia. Using outbound and inbound travel data, we assessed travel patterns from and to YF endemic countries in relation to China. Among YF endemic countries, Angola has the second highest number of travellers into China and also receives the second highest number of Chinese visitors. We estimated that China needs around half a million YF vaccine doses to cover their population travelling to YF endemic countries. The recent importation cases into China also unmasked the low YF vaccination coverage among Chinese travellers and workers to Angola, indicating the need to ensure better adherence to the International Health Regulations., (© International Society of Travel Medicine, 2017.. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Background: Travelers receive medical advice from a variety of sources, including travel agencies. The aim of this study is to describe the quality of pre-travel advice provided by travel agencies in Cuzco to travelers interested in visiting malaria and yellow fever endemic areas., Methods: Trained medical students posed as tourists and visited travel agencies in Cuzco requesting travel advice for a trip to the southern Amazon of Peru, recording advice regarding risk and prevention of malaria and yellow fever., Results: A total of 163 registered travel agencies were included in the study. The mean proposed tour duration was 6.8 days (±1.4 days) with a median time to departure of 3 days and a median tour cost of 805 US dollars (USD) [interquartile range (IQR) 580-1,095]. Overall, 45% employees failed to mention the risk for any illness. Eighteen percent of the employees acknowledged risk of malaria and 53% risk of yellow fever. However, 36% denied malaria risk and 2% denied risk of yellow fever in the region. The price of tours from travel agencies that did not mention any health risk was significantly lower [1,009.6 ± 500.5 vs 783.9 ± 402 USD, t (152) = 3, p < 0.01] compared with the price from agencies that did mention health risks. Almost all who acknowledged malaria (97%) and/or yellow fever (100%) were able to provide at least one recommendation for prevention. However, advice was not always accurate or spontaneously volunteered. Only 7% of the employees provided both correct scheduling and location information for administration of the yellow fever vaccine., Conclusions: The majority of registered travel agencies in Cuzco did not provide sufficient and accurate information regarding risk and prevention of malaria and yellow fever to travelers inquiring about trips to the southern Amazon of Peru., (© 2014 International Society of Travel Medicine.)

We describe travelers who were evaluated pre-travel to Brazil from March 2008 through July 2010 in the Boston area. Of 599 Brazil travelers, 71%, 58%, and 50% received vaccines for yellow fever (YF), typhoid, and hepatitis A, respectively. Fewer received influenza and hepatitis B vaccines (14%, 11%). A total of 60% traveled during Brazil's peak influenza season, and one fourth visited during peak dengue transmission. The 2014 World Cup and 2016 Olympics include events throughout Brazil. Travelers should seek pre-travel assessment including YF and malaria risk; travelers should be vaccinated against influenza, be up to date on other routine vaccines, and be prepared to protect themselves against mosquitoes., (© 2014 International Society of Travel Medicine.)

Background: Yellow fever (YF) vaccine is considered safe; however, severe illness and death following vaccination have been reported., Methods: Vaccine Safety Datalink (VSD) and US Department of Defense (DoD) data were used to identify adverse reactions following YF vaccination. Within the VSD, YF-vaccine-exposed subjects were compared to age-, site-, and gender-matched unexposed subjects. YF-vaccine-exposed DoD subjects were studied using a risk-interval design. For both cohorts, ICD-9 codes were analyzed for allergic and local reactions, mild systemic reactions, and possible visceral and neurologic adverse events (AEs)., Results: The VSD cohort received 47,159 doses from 1991 through 2006. The DoD cohort received 1.12 million doses from 1999 through 2007. Most subjects received other vaccines simultaneously. In the VSD cohort, rates of allergic, local, and mild systemic reactions were not statistically different between YF-vaccine-exposed and -unexposed subjects. In the DoD, there was an increased risk for outpatient allergic events in the period following vaccination with YF and other vaccines rate ratios [RR 3.85, 95% confidence interval (CI) 3.35-4.41] but with no increased risk for inpatient allergic reactions. In both cohorts, inpatient ICD-9 codes for visceral events were significantly less common following vaccination; inpatient codes for neurologic events were less common in the VSD YF-vaccine-exposed adult cohort, but did not differ between exposed and unexposed periods in the DoD. In the DoD, one fatal case of YF-vaccine-associated viscerotropic disease (YF-vaccine-AVD) was detected. The estimated death rate was 0.89 for 1,000,000 YF vaccine doses (95% CI 0.12-6.31/1,000,000 doses). No YF vaccine-associated deaths occurred in the VSD., Conclusions: In these closed cohorts we did not detect increased risk for visceral or neurologic events following YF vaccination. The death rate following YF vaccine was consistent with previous reports. These data support current recommendations for use of YF vaccine in young healthy individuals. These data are inadequate to judge safety of YF vaccines in elderly patients., (© 2013 International Society of Travel Medicine.)

Background: The number of international trips undertaken by French citizens is rising and we wished to assess the appropriateness of advices given to travelers in a vaccine and travel medicine center in France., Methods: We conducted a 3-month prospective study in one center in Paris where prescriptions and advice to travelers are given by trained physicians in travel medicine who have access to a computerized decision support system (Edisan). A questionnaire was used to record trip characteristics, patients' demographics, and prescriptions. Main outcome measure was the adequacy of prescriptions for malaria prophylaxis, yellow fever, and hepatitis A vaccines to French guidelines., Results: A total of 730 subjects were enrolled in this study, with a median age of 28 years. Travel destinations were sub-Saharan Africa (58%), Asia (21%), and South America (18%). Among the 608 patients (83%) traveling to malaria-endemic areas, malaria prophylaxis was in accordance with guidelines in 578/608 patients (95.1%, 95% CI: 93-96.5), and doxycycline was the regimen of choice (48%). Inappropriate malaria prophylaxis was given to eight patients, one of whom developed plasmodium falciparum malaria. All 413 patients (100%, 95% CI: 99-100) traveling to yellow fever-endemic areas who needed vaccination were correctly vaccinated. However, three patients received yellow fever vaccination without indication. Also, 442 of 454 patients (97.4%, 95% CI: 95.4-98.5) eligible to receive hepatitis A vaccination were immunized., Conclusion: Appropriate advice for malaria prophylaxis, yellow fever, and hepatitis A vaccinations was provided in a travel medicine and vaccine center where trained physicians used a computerized decision support system. Even in this setting, however, errors can occur and professional practices should be regularly assessed to improve health care., (© 2012 International Society of Travel Medicine.)

We report three cases of yellow fever (YF) in a family traveling from the city of Sao Paulo, Brazil (without previous vaccination) to an endemic area, acquiring the disease and presenting mild-to-moderate symptoms. Despite posing the intermittent risk of YF in endemic areas, it also alerts to the threat of introduction and spread of YF in the urban cycle, when infected travelers return to non-endemic areas where potential vectors are highly prevalent.

The dengue, West Nile, Japanese encephalitis and yellow fever viruses are important mosquito-borne viruses whose epidemiology is shifting in response to changing societal factors, such as increasing commerce, urbanization of rural areas, and population growth. All four viruses are expanding geographically, as exemplified by the emergence of West Nile virus in the Americas and Japanese encephalitis virus in Australasia. The large, recent global outbreaks of severe neurological disease caused by West Nile virus, the increasing frequency of dengue hemorrhagic fever outbreaks in the Americas, and the emergence of yellow fever virus vaccination-associated viscerotropic disease, are new clinical epidemiologic trends. These worrisome epidemiologic trends will probably continue in coming decades, as a reversal of their societal and biological drivers is not in sight. Nevertheless, the substantial reductions in Japanese encephalitis virus incidence resulting from vaccination programs and economic development in some Asian countries provide some encouragement within this overall guarded outlook.