WHO | Yellow fever – Senegal

From October to December 2020, a total of seven confirmed cases of yellow fever (YF) were reported from four health districts in three regions in Senegal. The outbreak consists of a set of four confirmed cases from three health zones in the Kidira health district, Tambacound region; one case in the neighboring Kedougou health district, Kedougou region; one case in Saraya Health District, Kedougou Region; and one case in the health district of Thilogne, Matam region.

In the Tambacounda region, on October 18, 2020, a sample was collected from a 40-year-old woman living in Kidira County during an investigation into West Nile virus infection. The Pasteur de Dakar Institute (IPD) confirmed the case on October 29 as yellow fever. On October 31, the IPD reported the results of the second confirmed YF case to national health authorities, following notification of Bakel Health Zone, Kidira Health District. The case involved an eight-year-old boy whose illness began in the Kidira health district and died on October 31st. On November 12, the IPD notified national health authorities of a third confirmed case, a 23-year-old man, who was discovered by routine surveillance and died on November 5. On November 16, a fourth confirmed case, a 15-year-old boy from the Kidira health district, was reported to the national health authorities. Two deaths among the four reported in the Kidira health district occurred in two hospitals: one at Matam Regional Hospital and the other at Tambacounda Regional Hospital.

In the Kedougou and Matam regions, three confirmed cases were recorded in December 2020, samples of which were collected during various investigations. In the Kedougou region, laboratory tests conducted by IPD found that of the 16 samples received from the region, there were:

• one confirmed case [polymerase chain reaction (PCR) and IgM positive] lives in Saraya district;
• one confirmed case [IgM positive and confirmed by plaque reduction neutralization test (PRNT)] lives in Kedougou County; and
• two presumed cases (IgM positive and ongoing PRNT).

In the Matam region, one case was confirmed as YF IgM and PRNT. The case is a 90-year-old man from Thilogne Health District, who was hospitalized at a private clinic in Dakar.

The Strategic Risk Assessment Tool (STAR), used prior to the notification of the third case in Kidira Health District, classified YF as “low,” where small outbreaks but probably not large outbreaks can be observed.

Public health response

The Ministry of Health coordinates a rapid response. Recommended response activities include immunization of the local population, enhanced surveillance, risk communication, community engagement, and vector control. The state may request additional potential vaccine support and operating costs.

WHO risk assessment

Detection of YF cases in the Tambacounda and Kedougou regions demonstrates the possibility of sylvatic spread of YF to unvaccinated people in rural areas and emphasizes the importance of maintaining high population immunity in all countries located in high-risk areas for YF. Recent epidemiological studies have reported that there are villages in the savannah area with non-human primates. Permanent or temporary pools of water are observed on the periphery of residential areas.

Although mass vaccination took place in Senegal in 2007, the eastern part of the country is considered to be at high risk of endemic YF transmission. Unvaccinated individuals remain susceptible to YF infection due to disease persistence in primates (sylvatic cycle), especially in rural areas. It is difficult to reach the two affected regions, which makes vaccination efforts a challenge. Intensive care units in the regions are far from the district (186 km) with poor road conditions. Affected neighborhoods are rural, mostly composed of forests, making it difficult to control vectors and mitigate the combined sylvatic-urban cycle.

The COVID-19 pandemic poses a risk of disrupting routine immunization activities due to strain on health systems and declining immunization reception due to physical distance or community reluctance. Discontinuation of immunization services, even for shorter periods, will increase the number of susceptible individuals and increase the likelihood of vaccine-preventable disease outbreaks. As of December 27, 2020, 18,523 confirmed COVID-19 cases and 387 deaths have been reported in Senegal.

WHO advice

YF is an acute viral hemorrhagic disease transmitted by infected mosquitoes and which can spread rapidly and have serious consequences for public health. There is no specific treatment, although the disease can be prevented with a single dose of the YF vaccine, which confers lifelong immunity. Supportive care is recommended for the treatment of dehydration, respiratory failure and fever, and antibiotic treatment for associated bacterial infections.

Senegal is considered a high-priority country with a strategy to eliminate the yellow fever epidemic (EYE). The introduction of YF vaccination into routine vaccination occurred in January 2005. Vaccination is the primary means of preventing and controlling YF. In urban centers, targeted vector control measures are also useful to stop transmission. The WHO and partners will continue to support local authorities in implementing these interventions to control the current epidemic.

The WHO recommends YF vaccination to all international travelers aged 9 months or older traveling to Senegal. Senegal also requires a YF vaccine certificate for travelers over 9 months of age or older from countries threatened by YF transmission and passengers who have spent more than 12 hours at the airport of the country threatening YF.

YF vaccination is safe, highly effective and offers protection for life. In accordance with international health regulations (2005), third edition, the validity of an international certificate of vaccination against YF extends to the life of the vaccinated person. An additional dose of YF vaccine may not be required from international travelers as a condition of entry.

The WHO has published guidelines for vaccination activities during the COVID-19 pandemic and is currently developing specific operational guidelines for conducting mass vaccination campaigns in the context of COVID-19. Where conditions allow, the EYE strategy will support the rapid continuation of YF prevention activities.

The WHO encourages Member States to take all necessary measures to keep passengers well informed about the risks and preventive measures, including vaccination. Passengers should also be aware of the signs and symptoms of YF and should consult a physician immediately when they show signs. The return of viremic passengers may pose a risk for the establishment of local YF transmission cycles in areas where the competent vector is present.

The WHO does not recommend any restrictions on travel and trade in Senegal based on the data available in this epidemic.

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