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11 Aug 2017

#Yellowfever in #Africa and the #Americas, 2016 (@WHO WER, August 11 ‘17)

Title: #Yellowfever in #Africa and the #Americas, 2016.

Subject: Yellow Fever virus activity in Africa and Americas Regions.

Source: World Health Organization (WHO), full PDF file: (LINK). Excerpt.

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Weekly epidemiological record / 11 AUGUST 2017, 92th YEAR / 437–452


Yellow fever in Africa and the Americas, 2016


In 2016, a total of 7509 suspected and 1080 laboratory-confirmed cases of yellow fever (YF), including 171 deaths, were reported to WHO during YF outbreaks in 6 countries.

In the WHO African Region, outbreaks were reported from Angola, the Democratic Republic of the Congo (DRC) and Uganda.

Most notably, 2 urban outbreaks in Angola and DRC reemphasized the threat of YF, and resulted in 963 laboratory-confirmed cases and 137 confirmed deaths (Table 1).

In the Region of the Americas, YF outbreaks were reported from Brazil, Colombia and Peru. The number of confirmed and probable cases reported from Peru has been the highest for the past 10 years; Brazil reported the beginning of a major outbreak in December 2016 (Table 2).

Yellow fever in Africa

Outbreaks in 2016

Since 2010, the East-Central African region has experienced a resurgence of YF outbreaks. In 2016, 3 countries, Angola, DRC and Uganda, reported outbreaks to WHO with a total of 7509 suspected and 970 laboratory-confirmed cases, including 130 confirmed deaths (casefatality rate (CFR): 13.4%).


The outbreak in Angola began in December 2015  when 3 cases were confirmed in Luanda province, capital of Angola. A total of 4188 suspected cases were reported, of which 3666 had samples tested; 884 were laboratory-confirmed. Laboratory-confirmed cases were reported in 16 of 18 provinces, and in 80 of 166 districts (Map 1). Overall 373 deaths (CFR: 8.9%) occurred among suspected cases and 121 deaths (CFR: 13.7%)  among confirmed cases. All age groups were affected; however, the age groups 10–14 years and 15–19 years accounted for 216 (24%) and 176 (20%), respectively, of the confirmed cases.

The date of onset of symptoms for the last confirmed case was 23 June 2016. Vaccination response activities began on 2 February 2017 in the first affected district of Luanda targeting those aged >6 months. As cases continued to be reported and confirmed, additional campaigns were organized in affected districts.

By the end of September, campaigns had been completed in 73 districts, with a cumulative total of 16 011 303 individuals vaccinated. Although an independent vaccination coverage survey has not yet been conducted, the administrative vaccination coverage was 95%. Angola declared the end of the outbreak on 23 December 2016. Historically, the last YF outbreak in Angola was reported from Luanda province in 1988.




The Democratic Republic of Congo

The first confirmed cases of YF in 2016 were confirmed in Kimpesi and Matadi health zones in the province of Kongo Central during the first and second week of March 2016. Shortly thereafter, 2 confirmed cases occurred in the health zone of Ndjili in Kinshasa. Investigation of these cases concluded that infection had occurred in Angola and therefore classified as imported cases. A total of 3256 suspected cases were reported, of which 2800 had specimens tested. Of these, 79 cases with 16 deaths (CFR: 21%) were confirmed, including 58 imported cases from Angola, 13 autochthonous and  8 sylvatic cases from the northern part of the country without link to the urban outbreak in Angola (Map 2). The mean age of confirmed cases was 31.9 years. Of the 58 imported cases, 35 were reported from the province of Kongo Central, 11 from Kinshasa, 11 from the  province of Kwango and one from the province of  Lualaba.

The date of onset for the last imported case occurred on 12 July 2016. DRC declared the end of the outbreak on 14 February 2017. A series of vaccination response campaigns were organized according to the extension of the outbreak. These were conducted primarily in zones bordering Angola and the city of Kinshasa. The first campaign from 26 May to 5 June targeted 9 health zones in the province of Kongo Central and 2 in Kinshasa. A second campaign was organized from 20 to 30 July targeting 1 health zone in Kinshasa and 4 in Kwango province. Given the risk of urban transmission, pre-emptive campaigns were organized from 17 to 26 August in the remaining 32 health zones of Kinshasa and in 15 health zones bordering Angola (Map 3).

The campaign in Kinshasa was conducted using fractional doses (1/5th of full dose) of vaccine for those aged >2 years. A final response campaign was conducted in the health zones of Feshi (Kwango province) and Mushenge (Kasai province) during the month of October when confirmed cases were identified. A cumulative total of 14 259 315 individuals were vaccinated, including 7 478 110 with fractional doses, with an administrative coverage of 103.5%. A post campaign vaccination coverage survey, conducted in the 62 health zones where vaccination occurred, showed coverage of 97.5%.





On 24 March 2016, an alert for a suspected haemorrhagic fever outbreak in Masaka district was received by the Ministry of Health (MoH). After further investigation and specimen collection, YF was confirmed in  3 persons of the same family from Kaloddo village. Between 24 March and 4 May, a total of 65 suspected cases and 7 confirmed cases, including 3 deaths, were reported from the districts of Masaka (5), Rukungiri (1) and Kalangala (1). In these 3 districts, a vaccination campaign was organized targeting those aged >6 months. A total of 627 706 individuals were vaccinated: 273 447 in Masaka district, 304 605 in Rukungiri district, and 49 654 in Kalangala district, with an overall vaccination coverage of 94% (91% in Masaka, 97% in Rukungiri and 95% in Kalangala).

Following the vaccination campaign in the affected districts, no additional cases were confirmed and the MoH declared the end of the outbreak on 6 September 2016. This is the first reported YF outbreak in southern areas of Uganda indicating that the entire country is at risk of YF epidemics.

Fractional doses of YF vaccine

In accordance with the global YF vaccine shortage, during the urban YF outbreaks in Angola and DRC, the first vaccination campaign with fractional doses of YF vaccine was implemented in Kinshasa province, DRC. With the recommendation of the Strategic Advisory Group of Experts (SAGE) on immunization, the campaign targeted those aged >2 years and successfully vaccinated a total of 7 478 110 individuals. An observational study assessing the immunogenicity of people vaccinated by fractional dose is in progress. The preliminary result at 28 days after vaccination showed that 98% (95% confidence interval [CI]: 96–99%) of study participants had seroconverted, which is equivalent to that of a full dose. The study will evaluate the long-term immunity of fractional dose of YF vaccine.

According to the WHO position paper,1 a fractional dose of YF vaccine is used only for emergency responses under a global YF vaccine shortage situation. For the administration of the vaccine, only a 10-vial presentation (or less) of 0.1 ml should be used to reduce the risk of contamination and deliver appropriate volumes. The success of the first practical implementation of a fractional dose of YF vaccine could highlight a potential solution for outbreak responses in case of YF vaccine shortage. However, practical problems remain: as longterm protection has not yet been scientifically demonstrated, vaccination with fractional dose does not meet YF vaccination requirements under International Health Regulations (IHR). At present, revaccination with a standard full dose is required for international travel. Furthermore, no standardized criteria for the implementation of fractional dose exist; current decisionmaking is based on the approval of each country. This ad-hoc decision-making process may defer implementation even in a vaccine shortage situation. To make best use of fractional dose of YF vaccine, further study and discussion are needed.

YF epidemics in new areas

From 2006 to 2016, a total of 227 YF events were reported from 19 countries in Africa and 7 in the Americas. The trend of events provides useful insight into forecasts and necessary preparedness for future YF outbreaks. During 2006–2016, 83% of YF events in Africa and 8% in the Americas occurred in areas where, from 1980 to 2005, YF events had never before been reported. This indicates that YF virus circulation, especially in Africa, has expanded to areas previously not at high risk. The shift is mainly attributed to the success of preventive mass vaccination campaigns (PMVCs) in YF high-risk countries (primarily countries in West Africa), increased population movements, altered land-use patterns, and climate change. Given that current environmental conditions clearly favour competent vectors, YF vaccination activities in the remaining YF endemic countries are critical and should be accelerated urgently. Furthermore, the increase in YF virus activity contributes to growing international concern that the YF virus may spread to Asian countries. To prevent further expansion of the virus, an urgent and coordinated approach is needed for YF control activities in current endemic countries.

Surveillance and laboratory system

In 2016, the YF surveillance system detected a total of 8524 suspected cases in 19 countries in Africa except Angola, DRC and Uganda. Of these suspected cases, blood specimens taken from 7063 cases were tested at national laboratories; 138 cases were YF IgM-ELISA positive. After confirmation using the plaque reduction neutralization test (PRNT) at a regional reference laboratory, 96 cases were classified as laboratory positive for YF in 9 countries: Burkina Faso (2), Cameroon (75), Congo (1), Côte d’Ivoire (5), Equatorial Guinea (2), Ghana (3), Guinea (5), Sao Tome and Principe (2), and Togo (1). However, laboratory-positive cases should be interpreted with care. For laboratory confirmation, determining the YF vaccination status is mandatory; nevertheless, this can be complicated by unreliable recall among individuals and the lack of retention of vaccination cards. Given vaccine-induced YF IgM being positive for several years after vaccination, and the increase in the number of countries having implemented PMVCs and introduced YF vaccine to national routine immunization, (primarily in West African countries), confirmation of vaccination status has become more important. A more centralized registration system of YF vaccination and different approaches for laboratory confirmation of suspected cases, including the testing for PCR in urine, need to be considered.
The urban YF outbreak in Angola exposed critical capacity issues facing the YF laboratory network at both national and regional level, such as limited capacity to confirm YF cases and shortage of funding and reagent supply, causing delayed laboratory confirmation and delayed response to YF epidemics.

To achieve early detection and early response to YF epidemics, strengthening the YF laboratory network is an urgent need.

Routine immunization

Routine immunization is central to YF control strategies. Since the recommendation by WHO and UNICEF in 1988 to incorporate YF vaccine into routine immunization programmes, 22 of 34 YF endemic countries have completed nationwide introduction. However, 2016 was a challenging year for routine immunization of YF. The unprecedented demand of YF vaccine for outbreak responses in Angola and DRC forced a halt in shipments planned for routine immunization which caused a YF vaccine stock-out in 15 of 23 target countries. Although WHO-UNICEF (WUNIC) estimates of vaccination coverage in 2016 have not yet been published, coverage is anticipated to decline in those countries, and fall below the target of 80%. Additionally, the quality of YF routine immunization has been at a suboptimal level – not only during 2016, but for previous decades.

For the past ten years, the average national YF routine Expanded Programme on Immunization (EPI) coverage of 22 countries in Africa, has been approximately 65–70%, below that of other major antigens (e.g. Bacillus Calmette-Guerin (BCG), polio (Pol3), diphtheria-tetanus-pertussis (DTP), and first dose of measles containing vaccine (MCV1)), and has never achieved the 80% target coverage.

Preliminary results of a health facility-based field survey in 4 YF high-risk countries (Benin, Liberia, Senegal and Togo) revealed that deficiencies in YF routine immunization are largely due to the fragile health systems of target countries. Most districts with low YF vaccination coverage are confronted with the following health system related issues: (i) inaccurate population data; (ii) problems relating to human resources; (iii) a lack of motorbikes for outreach; (iv) a shortage of cold chain; and (v) limited supervision (Figure 1). The low average vaccination coverage of DTP32 in 22 countries introducing YF routine immunization (only 75% in 2015, despite global coverage being 86% in 2015) highlighted the urgent need for strengthening health system in those countries.

Although each country is responsible for strengthening their health system and routine immunization, most YF endemic countries are low- or lowermiddle-income countries with limited capacity. Given that YF control is an international, not a national, issue, the YF vaccination programme, in collaboration with other vaccine preventable disease programmes, needs to communicate closely with, and actively support, YF endemic countries to attain optimal vaccination coverage of YF routine immunization.

Risk assessment

YF risk assessment in countries within the endemic transmission zone is an important component of YF control efforts.

Analysis provides the evidence to decide the national YF control strategy (i.e. introduction of YF routine immunization, implementation of PMVC, introduction of case-based surveillance system, and application of the IHR) based on an estimation of the seroprotection level of the population, the presence of the virus, and the density of the implicated vectors. While the number of countries completing a YF risk assessment, either by mathematical modelling or cross-sectional survey, has increased, many countries within the transmission zone have yet to complete them (Table 3). The completion of YF risk assessment should be a priority for YF control in the African Region.

Yellow fever in the Americas


In 2016, a total of 110 laboratory-confirmed cases of YF with 31 deaths (CFR: 28.2%) were reported from 3 countries: Brazil (41 cases), Colombia (7 cases), and Peru (62 cases).


In Brazil, during January–May 2016, 5 confirmed cases of YF were reported, including 4 deaths (CFR: 80%). The cases occurred in the states of Goias (3 cases), Amazonas (1 case), and São Paulo (1 case). From June to early December only 1 additional case was reported. Nevertheless, December 2016 marked the beginning of the largest outbreak of YF in the country for the past 50 years and included areas considered outside  the risk area for YF. During the investigation of the outbreak, 35 cases were identified with onset of symptoms dated as December 2016: 33 in Minas Gerais and 2 in São Paulo state. The demographic of confirmed cases is similar to that generally observed during YF outbreaks, with a high proportion of males of economically-active age.

In non-human primates, 8 epizootics due to YF virus were confirmed during January–May, and 16 during August–December. Since July 2014, 6 states (Pará, Tocantins, Goiás, Distrito Federal, Minas Gerais, and São Paulo) reported 163 confirmed epizootics of YF. Brazil has been implementing both PMVCs and routine EPI for YF control for some decades. From 2007 to 2016, a total of 71 725 759 doses of YF vaccine was allocated to the target population.


In Colombia, from week 1 to week 52 of the epidemic in 2016, 12 cases of jungle YF were reported: 7 laboratoryconfirmed cases and 5 probable cases. The 7 confirmed cases were male (some were military personnel); 57% were aged between 20 and 29 years. Of the 7 confirmed cases, 6 died (CFR: 85.7%). Confirmed cases originated in the following departments: Meta (2 cases), Vichada  (1 case), Vaupés (1 case), Chocó (1 case), Guainía (1 case) and 1 imported case from Peru. Probable cases were from the departments of Córdoba (1 case), Vichada (2 cases), Vaupés (1 case), and Santa Marta (1 case). The confirmation of cases in the Vichada Department (bordering with the Bolivarian Republic of Venezuela), the Chocó Department (bordering with Panama), and the Guainía Department (bordering with the Bolivarian Republic of Venezuela and Brazil) poses a risk to the bordering countries, particularly in areas with a shared ecosystem.


In Peru, 62 confirmed and 2 probable cases of jungle YF cases were reported in 2016, including 25 deaths. This is the highest number of cases reported by the country for the past 10 years, although Peru showed certain progress on YF control after the development of an accelerated plan for vaccination from 2004 to 2007. The confirmed and probable cases were geographically distributed in the following departments: Junin (44 cases), San Martin (5 cases), Ayacucho (5 cases), Amazonas (3 cases), Huanuco (3 cases), Ucayali  (2 cases), Cajamarca (1 case) and Cusco (1 case), allocated in areas of 48 provinces considered at risk of YF in the country. As regards the YF routine EPI, national vaccination coverage for the past 4 years has been approximately 64.6%, ranging from 62.0% to 67.1%, falling below the target of 80%.

Routine YF vaccination coverage

In South America, YF vaccination has been ongoing for at least 3 decades. Up to 1991, PMVCs were carried out every 5 years in the endemic countries of the region. Since 1998, integration of the YF vaccine within national child immunization programmes has become well established. By the end of 2007, the average reported vaccination coverage had reached 86% for these countries. Table 4 shows the progress on YF vaccination in 3 countries in the Americas. Currently, 2 major concerns remain regarding vaccination: one is the movement of unvaccinated people from coastal areas, where vaccination is not carried out, to the more inland endemic areas. The second is the resurgence and spread of the urban form of the disease as a result of the recent re-invasion of the continent by the urban-dwelling mosquito vector.

Since 2011, most countries with enzootic areas have introduced YF vaccine into their vaccination schedules as part of the EPI. In Brazil, Argentina and Suriname, routine YF vaccination is provided in areas considered at risk. Although there is an increasing use of YF vaccine in EPI schedules, vaccination coverage in children aged 1 year has not exceeded a rate of approximately 70%. The factor responsible for limiting coverage rates has been insufficient availability of the vaccine. The global supply of YF vaccines has been limited for some years. However, the PAHO Revolving Fund system has undertaken the necessary actions to obtain adequate supplies and provides approximately 50% of demand in the Region of the Americas. The Revolving Fund allocates vaccines based on country epidemiological risk.


Keywords: WHO; Updates; Yellow Fever; Africa & Americas Regions.