Differences between coverage of yellow fever vaccine and the first dose of measles-containing vaccine: A desk review of global data sources.

INTRODUCTION: The strategy to Eliminate Yellow Fever Epidemics (EYE) is a global initiative that includes all countries with risk of yellow fever (YF) virus transmission. Of these, 40 countries (27 in Africa and 13 in the Americas) are considered high-risk and targeted for interventions to increase coverage of YF vaccine. Even though the World Health Organization (WHO) recommends that YF vaccine be given concurrently with the first dose of measles-containing vaccine (MCV1) in YF-endemic settings, estimated coverage for MCV1 and YF vaccine have varied widely. The objective of this study was to review global data sources to assess discrepancies in YF vaccine and MCV1 coverage and identify plausible reasons for these discrepancies. METHODS: We conducted a desk review of data from 34 countries (22 in Africa, 12 in Latin America), from 2006 to 2016, with national introduction of YF vaccine and listed as high-risk by the EYE strategy. Data reviewed included procured and administered doses, immunization schedules, routine coverage estimates and reported vaccine stock-outs. In the 30 countries included in the comparitive analysis, differences greater than 3 percentage points between YF vaccine and MCV1 coverage were considered meaningful. RESULTS: In America, there were meaningful differences (7-45%) in coverage of the two vaccines in 6 (67%) of the 9 countries. In Africa, there were meaningful differences (4-27%) in coverage of the two vaccines in 9 (43%) of the 21 countries. Nine countries (26%) reported MVC1 stock-outs while sixteen countries (47%) reported YF vaccine stock-outs for three or more years during 2006-2016. CONCLUSION: In countries reporting significant differences in coverage of the two vaccines, differences may be driven by different target populations and vaccine availability. However,these were not sufficient to completely explain observed differences. Further follow-up is needed to identify possible reasons for differences in coverage rates in several countries where these could not fully be explained.

The Public Health Benefits and Economic Value of Routine Yellow Fever Vaccination in Colombia.

OBJECTIVES: To evaluate the public health benefits and economic value of live-attenuated yellow fever (YF) 17D vaccine in Colombia. METHODS: A decision tree model was used to assess the theoretical impact of routine YF vaccination of 1-year-olds (no "catch-up") during the interepidemic period from 1980 to 2002, avoiding capturing the impact of YF vaccine introduction in 2003. The vaccine was assumed to be 99% effective, to provide lifetime protection, and to cover 85% of the target population. Costs per disability-adjusted life-year (DALY) averted were computed from payer and societal perspectives. Univariate sensitivity analyses were performed. RESULTS: During the interepidemic period, routine YF vaccination would have averted 2223 nonfatal cases of YF and 65 deaths, leading to an overall reduction of 1365 DALYs. The net cost of this vaccination would have been $25 964 813 (payer's perspective) and $16 535 465 (societal perspective). Cost per DALY averted was $19 022 and $12 114 from payer and societal perspectives, respectively (all costs in 2015 US dollars). Vaccination was considered cost-effective from both perspectives (ie, between 1- and 3-fold the gross domestic product per capita, $7158) and remains so if price per dose was $2.75 or less and $4.66 from payer and societal perspectives, respectively. Underreporting had the largest impact on the results. CONCLUSIONS: Routine toddler YF vaccination in Colombia would have been considered cost-effective in the prevaccination era. This study provides insights on the value of vaccination in an upper middle-income country.

Is the absence or intermittent YF vaccination the major contributor to its persistent outbreaks in eastern Africa?

Despite the availability of a safe and efficacious yellow fever vaccine since 1937, yellow fever remains a public health threat as a re-emerging disease in Africa and South America. We reviewed the trend of reported yellow fever outbreaks in eastern African countries, identified the risk epidemiological factors associated with the outbreaks and assessed the current situation of Yellow Fever vaccination in Africa. Surveillance and case finding for yellow fever in Africa are insufficient primarily due to lack of appropriate diagnostic capabilities, poor health infrastructure resulting in under-recognition, underreporting and underestimation of the disease. Despite these challenges, Ethiopia reported 302,614 cases (30,505 deaths) in 1943-2015, Kenya had 207 cases (38 deaths) in 1992-2016, Sudan experienced 31,750 suspected cases (1855 deaths) from 1940 to 2012 and Uganda had 452 cases (65 deaths) in 1941-2016. Major risk factors associated with past yellow fever outbreaks include climate, human practices and virus genetics. Comparisons between isolates from different outbreaks after 45 years have revealed the genetic stability of the structural proteins of YFV which are the primary targets of the host immune cells. This probably explains why yellow fever 17D vaccine is considered as outstandingly efficacious and safe after being used for 75 years. However, the 14 amino-acid changes among these isolates may have a greater impact on the changing disease epidemiology, virulence and transmission rate. Low population immunity against YF influences outbreak frequency especially in countries where the incorporation of YF vaccination is not combined with mass vaccination campaigns or vaccination is limited to international travellers. Understanding Yellow fever virus epidemiology as determined by its evolution underscores appropriate disease mitigation strategies and immunization policies. Mobilizing scarce resources to enhance population immunity through sufficient vaccination, promoting environmental sanitation/hygienic practices, driving behavioral change and community-based vector control are significant to preventing future epidemics.

Is it time for a new yellow fever vaccine?

An inexpensive live attenuated vaccine (the 17D vaccine) against yellow fever has been effectively used to prevent yellow fever for more than 70 years. Interest in developing new inactivated vaccines has been spurred by recognition of rare but serious, sometimes fatal adverse events following live virus vaccination. A safer inactivated yellow fever vaccine could be useful for vaccinating people at higher risk of adverse events from the live vaccine, but could also have broader global health utility by lowering the risk-benefit threshold for assuring high levels of yellow fever vaccine coverage. If ongoing trials demonstrate favorable immunogenicity and safety compared to the current vaccine, the practical global health utility of an inactivated vaccine is likely to be determined mostly by cost.

[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.