WHO alerts – Disease outbreak news – Venezuela reported seven confirmed human cases of yellow fever

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Disease outbreak news – Venezuela (Bolivarian Republic of)

14 October 2021

On 1 October 2021, the IHR National Focal Point (NFP) for Venezuela reported seven confirmed human cases of yellow fever which were investigated between 23 and 24 September 2021. All seven caes were confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) at the Rafael Rangel National Hygiene Institute. Six of the seven reported cases were not vaccinated. Of these, three were asymptomatic and four developed signs and symptoms between 20 to 24 September, all presented fever and one of the cases also presented with a headache, retro ocular pain, arthralgias and a skin rash. The probable location of infection was a rural parish locality, south of the Maturín Municipality in the Monagas State, which is in the northeast region of Venezuela. The first reported case was a young pregnant woman with a history of yellow fever vaccination. Of the remaining six cases, five were male and ranged between 24 and 82 years of age.To date, no deaths have been reported among the confirmed cases.

Additionally, between 11 August and 1 October 2021, 10 epizootics among non-human primates (NHP) were reported in Venezuela as part of the routine national surveillance. Seven epizootics were located in Monagas state (in the municipalities of Maturin and Aguasay (70 km from Maturin municipality) and three in Anzoátegui state (Freites Municipality, 159 km from Maturin municipality). Two of the epizootics were laboratory confirmed by RT-PCR at the National Reference Laboratory (LNR) both reported in Monagas State and eight (five from Monagas and three from Anzoátegui) were confirmed by an epidemiological link (given the time-space relationship with laboratory confirmed epizootics). Confirmed epizootics were identified at 35 km and 150 km from the urban area of Maturín within the state of Monagas. 

Public health response

National and local health authorities in Venezuela are implementing public health measures, including the following:

  • Strengthening surveillance both in humans and NHPs.
  • Strengthening laboratory diagnosis for humans and NHPs.
  • Strengthening entomological surveillance, as well vector control in urban areas.
  • Raising aedic index in prioritized communities, with an emphasis on arbovirus endemic geographic areas.
  • Capture of sylvatic vectors for identification of the species and virological study.
  • Strengthening case management protocols and the organization of health care facilities.
  • Deployment and roll out of vaccination with yellow fever vaccine in the country. In the framework of the yellow fever outbreak response plan, a total of 24,772 doses have been administered in the municipalities of Aguasay, Maturín, Santa Bárbara, Ezequiel Zamora, and Cedeño of the Monagas state, reaching a coverage of 68.3%, this activity was carried out as part of the vaccination campaign in prioritized municipalities since 1 November 2020 which continues to be intensified since the occurrence of epizootics in Monagas and Anzoátegui states.
  • Since 11 August 2021, activities to intensify vaccination started in Monagas State (Marutín Municipality), and Anzoategui State (Guanipa, Simón Rodríguez and Anaco municipalities) and are still ongoing.
  • Rapid vaccination coverage monitoring is ongoing in areas where epizootics were confirmed.
  • Strengthening activities for the control of Aedes aegypti infestation, as a possible vector in urban areas.
  • Risk communication strategies. 

WHO risk assessment

Yellow fever is an acute viral haemorrhagic disease caused by the yellow fever virus (YFV) and is transmitted by infected mosquitoes of the genera Haemagogus and Sabethes, as well as the urban mosquito species Aedes aegypti.  Yellow fever infects humans and non-human primates (NHP) and has the potential to spread rapidly and cause serious public health impact in unimmunized populations. Vaccination is the most important means of preventing the infection as the disease is preventable with a single dose of yellow fever vaccine which provides immunity for life. While there is no specific treatment, supportive care to treat dehydration, respiratory failure and fever and antibiotic treatment for associated bacterial infections can reduce mortality and is recommended. Viraemic cases should stay under mosquito nets during the day to limit the risk of spread to others through bites of mosquitoes, and vector control strategies may complement particularly during outbreaks.

Venezuela is considered high risk for yellow fever with endemic virus transmission and is a priority country for the global Eliminate Yellow fever Epidemics (EYE) strategy. Vaccination coverage is suboptimal, creating a high risk for onward transmission and amplification of yellow fever among unvaccinated populations.

The increased number of human cases and epizootics since August 2021, is concerning due to the persistence of high viral circulation. Since November 2020, when the vaccination campaign began in prioritized states, 82% immunization coverage has been achieved, with five out of the 10 states with 100% coverage (Amazonas, Apure, Delta Amacuro, Sucre and Táchira). The remaining five states vary in vaccine coverage (Anzoátegui 97.2%, Guárico 95.5%, Bolívar 78.9%, Monagas 67.7%, and Zulia 44.7%). The state where the outbreak has occurred, Monagas state, has low vaccination coverage which suggests a significant population remains at-risk with a necessity to intensify risk communications among high-risk groups.

Despite the significant efforts made to vaccinate a large portion of the population, the increasing number of human cases and the persistence and geographical spread of epizootics among NHP illustrate the potential risk of further spread to areas where YF immunization coverage is low. Special attention should also be placed on specific at-risk groups and ethnic minorities. There is a long-standing pattern of movements of indigenous people across borders among settlements of the same culture, including to neighbouring Trinidad and Tobago. According to the International Organization for Migration[i], the flow of Warao people moving from their villages in Venezuela to Brazil, to Guyana and possibly to Suriname has increased dramatically since 2017 and persisted during the COVID-19 pandemic.

The Monagas State and national level governments along with the PAHO/WHO field team carried out activities to intensify surveillance among NHPs and entomological populations, as well as vector control in urban areas. However, epizootic and entomological surveillance needs to be strengthened in the affected and surrounding areas where human cases were detected.

 The yellow fever outbreak in Venezuela is occurring in the context of a major and complex situation, which includes the COVID-19 pandemic. The pandemic creates a risk of disruption access to health care due to COVID-19 related burdens on the health system, lack of health workers along with decreased vaccination demand due to physical distancing requirements or community reluctance.

The capacity of local laboratories and national reference laboratories may also be compromised due to the increased demand in processing COVID-19 samples. As of 13 October, Venezuela reported 384 668 COVID 19 cases and 4634 deaths, and currently is among the eight countries with the highest number of COVID-19 new cases in the last 24 hours in the Region of the Americas.

All yellow fever endemic and high risk regions and territories are also experiencing ongoing transmission of SARS-CoV-2, the addition of YFV as a co-circulating virus could pose an additional challenge for case management and infection and prevention control activities if there was a large scale yellow fever outbreak in Venezuela or neighbouring countries.

WHO continues to monitor the epidemiological situation and review the risk assessment based on the latest available information.

WHO advice

The reported YF cases illustrate the importance of maintaining awareness of the need for yellow fever vaccination, especially in endemic high-risk areas with favorable ecosystem for yellow fever transmission.

Vaccination is the primary means for prevention and control of yellow fever. Vaccination coverage should be increased particularly in people living and working in forested areas, who are exposed during the day to sylvatic vectors (Haemagogus spp and Sabethes spp­). Vaccination coverage should also be increased among indigenous populations, migrants and other vulnerable populations who often live in densely populated urban areas (with a risk of urban local transmission via Aedes agyepti) or participate in activities in forested areas (with a risk of sporadic cases or clusters in a sylvatic context). 

WHO recommends vaccination against yellow fever for all international travellers over 9 months old at least 10 days prior to travel to Venezuela (see map here). Venezuela does not request a vaccination certificate for incoming travellers.

Yellow fever vaccination recommended by WHO is safe, highly effective and provides life-long protection. In accordance with the IHR (2005), third edition, the validity of the international certificate of vaccination against yellow fever extends to the life of the person vaccinated with a WHO approved vaccine. A booster dose of approved yellow fever vaccine cannot be required of international travellers as a condition of entry.

WHO has published guiding principles for immunization activities during the COVID-19 pandemic and operational guidance for conducting mass vaccination campaigns in the COVID-19 context. The EYE strategy promotes maintaining and improving vaccination against YF of all eligible children in routine services and supports campaigns for large-scale populations where required according to WHO guidelines for implementation in COVID-19.

WHO encourage its Member States to take all actions necessary to keep travellers well informed of risks and preventive measures including vaccination. Travellers should also be made aware of yellow fever signs and symptoms and instructed to rapidly seek medical advice when presenting with any of them. Infected (viraemic) returning travellers may pose a risk for the establishment of local cycles of yellow fever transmission in areas where a competent vector is present.

WHO does not recommend any restrictions on travel and trade to Venezuela on the basis of the information available on this event.

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