Eliminating yellow fever epidemics in Africa: Vaccine demand forecast and impact modelling.

BACKGROUND: To counter the increasing global risk of Yellow fever (YF), the World Health Organisation initiated the Eliminate Yellow fever Epidemics (EYE) strategy. Estimating YF burden, as well as vaccine impact, while accounting for the features of urban YF transmission such as indirect benefits of vaccination, is key to informing this strategy. METHODS AND FINDINGS: We developed two model variants to estimate YF burden in sub-Saharan Africa, assuming all infections stem from either the sylvatic or the urban cycle of the disease. Both relied on an ecological niche model fitted to the local presence of any YF reported event in 34 African countries. We calibrated under-reporting using independent estimates of transmission intensity provided by 12 serological surveys performed in 11 countries. We calculated local numbers of YF infections, deaths and disability-adjusted life years (DALYs) lost based on estimated transmission intensity while accounting for time-varying vaccination coverage. We estimated vaccine demand and impact of future preventive mass vaccination campaigns (PMVCs) according to various vaccination scenarios. Vaccination activities conducted in Africa between 2005 and 2017 were estimated to prevent from 3.3 (95% CI 1.2-7.7) to 6.1 (95% CI 2.4-13.2) millions of deaths over the lifetime of vaccinees, representing extreme scenarios of none or maximal herd effects, respectively. By prioritizing provinces based on the risk of urban YF transmission in future PMVCs, an average of 37.7 million annual doses for PMVCs over eight years would avert an estimated 9,900,000 (95% CI 7,000,000-13,400,000) infections and 480,000 (180,000-1,140,000) deaths over the lifetime of vaccinees, corresponding to 1.7 (0.7-4.1) deaths averted per 1,000 vaccine doses. CONCLUSIONS: By estimating YF burden and vaccine impact over a range of spatial and temporal scales, while accounting for the specificity of urban transmission, our model can be used to inform the current EYE strategy.

Preferences and decision needs of Boston-area travelers to countries with risk of Yellow fever virus transmission: implications for health care providers.

BACKGROUND: Yellow fever (YF), a potentially fatal mosquito-borne infection, is preventable with a live-attenuated vaccine, rarely associated with severe adverse events. We surveyed travelers to assess their reasons for pre-travel medical consultation, information they considered important regarding YF disease and vaccination, whether they recalled receiving this information, and whether they were involved in vaccine decision-making. METHODS: Travelers aged 18 years and older were surveyed at three Boston-area travel clinics. Only those making YF vaccination decisions were included for analyses. RESULTS: Of 831 travelers surveyed, 589 (70%) indicated making a YF vaccination decision. Travel medicine providers recommended YF vaccination to 537 (91%) of 589 travelers; 92% of these 537 received vaccine. Among 101 travelers aged 60 years and older, 9% declined the vaccine; among those younger than 60 years, 4% declined the vaccine (p = 0.06). Of 589 travelers, most agreed they needed to understand destination-specific YF risks (82%) and vaccine risks (88%), and were involved in YF vaccine decisions (87%). Less than half recalled discussing their concerns about YF vaccine with the provider (42%) or what risks and benefits mattered most to them (32%). CONCLUSION: Most participants sought YF disease and vaccine risk information and wanted to be involved in decision-making; however, fewer than half recalled discussing their opinions or concerns about YF vaccine. Providers need effective risk communication skills and the ability to elicit and respond to travelers' concerns to help them make informed, shared decisions.

Serologic assessment of yellow fever immunity in the rural population of a yellow fever-endemic area in Central Brazil.

INTRODUCTION: The yellow fever epidemic that occurred in 1972/73 in Central Brazil surprised the majority of the population unprotected. A clinical-epidemiological survey conducted at that time in the rural area of 19 municipalities found that the highest (13.8%) number of disease cases were present in the municipality of Luziânia, State of Goiás. METHODS: Thirty-eight years later, a new seroepidemiological survey was conducted with the aim of assessing the degree of immune protection of the rural population of Luziânia, following the continuous attempts of public health services to obtain vaccination coverage in the region. A total of 383 volunteers, aged between 5 and 89 years and with predominant rural labor activities (75.5%), were interviewed. The presence of antibodies against the yellow fever was also investigated in these individuals, by using plaque reduction neutralization test, and correlated to information regarding residency, occupation, epidemiological data and immunity against the yellow fever virus. RESULTS: We found a high (97.6%) frequency of protective titers (>1:10) of neutralizing antibodies against the yellow fever virus; the frequency of titers of 1:640 or higher was 23.2%, indicating wide immune protection against the disease in the study population. The presence of protective immunity was correlated to increasing age. CONCLUSIONS: This study reinforces the importance of surveys to address the immune state of a population at risk for yellow fever infection and to the surveillance of actions to control the disease in endemic areas.

Serologic assessment of yellow fever immunity in the rural population of a yellow fever-endemic area in Central Brazil

Introduction The yellow fever epidemic that occurred in 1972/73 in Central Brazil surprised the majority of the population unprotected. A clinical-epidemiological survey conducted at that time in the rural area of 19 municipalities found that the highest (13.8%) number of disease cases were present in the municipality of Luziânia, State of Goiás. Methods Thirty-eight years later, a new seroepidemiological survey was conducted with the aim of assessing the degree of immune protection of the rural population of Luziânia, following the continuous attempts of public health services to obtain vaccination coverage in the region. A total of 383 volunteers, aged between 5 and 89 years and with predominant rural labor activities (75.5%), were interviewed. The presence of antibodies against the yellow fever was also investigated in these individuals, by using plaque reduction neutralization test, and correlated to information regarding residency, occupation, epidemiological data and immunity against the yellow fever virus. Results We found a high (97.6%) frequency of protective titers (>1:10) of neutralizing antibodies against the yellow fever virus; the frequency of titers of 1:640 or higher was 23.2%, indicating wide immune protection against the disease in the study population. The presence of protective immunity was correlated to increasing age. Conclusions This study reinforces the importance of surveys to address the immune state of a population at risk for yellow fever infection and to the surveillance of actions to control the disease in endemic areas. .

Active assessment of adverse events following yellow fever vaccination of persons aged 60 years and more.

INTRODUCTION: Older age has been associated to serious adverse events (AE) following yellow fever (YF) vaccination in passive surveillance studies, but few prospective studies involving seniors have been published. RESULTS: A total of 906 persons were evaluated; 78 were not vaccinated and 828 received the vaccine; 700 (84.7%) were interviewed after vaccination: 593 (84.7%) did not report any symptoms or signs following YF vaccine; 107 (15.3%) reported at least one AE temporally associated to YF vaccination: 97 (13.9%) had systemic AE and 17 (2.4%) reported AE at the injection site (7 had both systemic and local AE). Data regarding previous vaccination was available for 655 subjects. Statistically significant higher rates of systemic AE were observed among subjects who received the first YF vaccination (17.5%) in comparison to persons who had been previously vaccinated (9.5%). METHODS: This observational prospective study aimed to describe AE following YF vaccination in persons aged ≥ 60 y. From March 2009 to April 2010, seniors who sought YF vaccination at a reference Immunization Center in São Paulo city, Brazil, were included. Demographic and clinical data, previous YF vaccination, travel destination and the final decision regarding YF vaccination or not were collected from standardized medical records. Active AE assessment was done through telephone or electronic mail interview performed approximately 14 d after immunization. CONCLUSION: Most persons aged ≥ 60 y may be safely vaccinated against YF. Before vaccination, they must be carefully screened for conditions associated to altered immunocompetence and for risk of exposure to YF.

[Estimated operational costs of vaccination campaign to combat yellow fever in Abidjan]. / Coûts de la riposte vaccinate contre la fièvre jaune à Abidjan, 2001.

A cost effectiveness study was conducted with the main objective to assess the operational costs of a vaccination campaign against yellow fever organised and implemented in Abidjan from September 21st to October 2nd, 2001. The study was carried out from the perspective of the health authorities. Data was collected retrospectively on all information related to resources needed and required activities. The justification of the monetary value of resources was provided with written proof and receipts as well as other supporting documents. The coverage achieved was 91.33% with 2 584 360 doses of vaccine having been administered. Spending on vaccines and vaccine supplies amounted to 1 123 177 128 FCFA; the average cost per dose was 539.40 FCFA. Human resource costs amounted to 2590 people who were mobilized for a total cost of 125 678 400 FCFA. The total operational cost of the vaccination campaign was 1 394 010 829 FCFA. Vaccines and supplies were the largest item of expenditure, or 80.57% of the total spent. The results of this study could serve as a tool for decision-making related to funding a vaccination campaign. Taking account of these results could contribute to the development of strategies to effectively reduce the operational cost of a vaccination campaign.

Vaccination coverage survey versus administrative data in the assessment of mass yellow fever immunization in internally displaced persons--Liberia, 2004.

Yellow fever (YF) is a mosquito-borne vaccine-preventable disease with high mortality. In West Africa, low population immunity increases the risk of epidemic transmission. A cluster survey was conducted to determine the effectiveness of a mass immunization campaign using 17D YF vaccine in internally displaced person (IDP) camps following a reported outbreak of YF in Liberia in February 2004. Administrative data of vaccination coverage were reviewed. A cluster sample size was determined among 17,384 shelters using an 80% vaccination coverage threshold. A questionnaire eliciting demographic information, household size, and vaccination status was distributed to randomly selected IDPs. Data were analyzed to compare vaccination coverage rates of administrative versus survey data. Among 87,000 persons estimated living in IDP camps, administrative data recorded 49,395 (57%) YF vaccinated persons. A total of 237 IDPs were surveyed. Of survey respondents, 215 (91.9%, 95% CI 88.4-95.4) reported being vaccinated during the campaign and 196 (83.5%, 95% CI 78.6-88.5) possessed a valid campaign vaccination card. The median number of IDPs living in a shelter was 4 (range, 1-8) and 69,536 persons overall were estimated to be living in IDP camps. Coverage rates from a rapid survey exceeded 90% by self-report and 80% by evidence of a vaccination card, indicating that the YF immunization campaign was effective. Survey results suggested that administrative data overestimated the camp population by at least 20%. An emergency, mop-up vaccination campaign was avoided. Coverage surveys can be vital in the evaluation of emergency vaccination campaigns by influencing both imminent and future immunization strategies.