Yellow Fever – Republic of South Sudan

On 3 March 2020, the WHO supported a cross-border rapid reaction investigation identified two suspected positive cases of yellow fever in Kajo Keji district, Central Equatorial State, South Sudan. The first polymerase chain reaction (PCR) test conducted at the National Public Health Laboratory in Juba, South Sudan, rated it negative. However, upon further testing, both cases were confirmed positive for yellow fever by testing for plaque reduction neutralization (PRNT) at the Regional Reference Laboratory, Uganda Research Institute (URI) on March 28.

An investigation has been launched in response to the recently declared border outbreak in Moyo district, Uganda. During the investigation, the team collected 41 blood samples from five villages close to Moyo district in Uganda. Among the 41 specimens whose samples were collected, nine (22%) had fever, but none had jaundice. Individuals represented a spectrum of interest in the area (agriculture, forestry, domestic worker, soldier). Most of the interviewees were between the ages of 20 and 45, and 18 (44%) of them were women.

In addition, rapid entomological research in the villages has found evidence of multiple mosquito breeding sites and abundant Aedes mosquito species (e.g. aegypti . albopictus. The Simpsons).

As of March 28, 2020, these are the only two cases (no fatalities) confirmed from Kajo Keji County.

South Sudan has experienced several outbreaks of yellow fever in the past. The last outbreak was declared on November 29, 2018 in Sakure payam, Nzara County, Gbudue State (the present state of Western Equatoria), when three laboratory confirmed cases with no associated cases were reported. In order to respond to the epidemic, a targeted reactive vaccination action was put in the affected area. Prior to this outbreak, in May 2003, a total of 178 cases were recorded with 27 deaths in Imatong region, Torit State, South Sudan. A reactive vaccination campaign was launched in response to the 2003 epidemic.

Public health response

• The country quickly established an in-depth multidisciplinary investigation in Kajo Keji district in response to a cross-border outbreak notification in Moyo, Uganda. The tests included enhanced surveillance, active case finding and entomological testing from February 12 to 18 with support from WHO offices and headquarters.
• Supervision has been strengthened in the context of Integrated Disease Control and Response (IDSR) by training health professionals and expanding the definition of yellow fever to healthcare facilities to improve case detection and reporting.
• In light of the country’s current COVID-19 epidemic, the World Health Organization office and partners have hired the Ministry of Health to determine when reactive vaccinations can be carried out in the Kajo Keji country. An International Coordination Group (ICG) request was submitted for the proposed campaign.
• Appropriate discussions are also underway with the Ministry of Health on proposed campaigns for preventive mass vaccination and the introduction of vaccination against yellow fever into the routine immunization schedule by 2022.

WHO risk assessment

Yellow fever is an acute viral hemorrhagic disease transmitted by infected mosquitoes and can spread rapidly and cause serious public health impact. Vaccination is the most important means of preventing infection, which provides immunity for life.

The risk of further and further transmission of yellow fever is concerned in South Sudan by:

• Confirmed outbreak in the Uganda border area, along with a continuous savanna and forest biome with common mosquito vectors and non-human primates;
• Deficiencies in monitoring and weakness in health services could delay the rapid detection of additional yellow fever cases;
• Negligible population immunity;
• Permanent immigration to Kajo Keji, including over 13,200 returnees to the county, primarily from Uganda in recent weeks, is an influx of new vulnerable people into the county;
• Ongoing controls at the borders (air / ground) related to COVID-19 are expected; however, as the borders between the Democratic Republic of the Congo, Uganda and South Sudan are porous with significant cross-border social and economic activities, the risk of transference cannot be ruled out;
• The current rainy season, which began in early March, is expected to increase vector load in the coming weeks, thereby increasing the risk of yellow fever transmission.

Careful monitoring of the situation with active cross-border coordination and exchange of information is needed.

Based on the information available, WHO estimates that the overall risk is high at national and regional level.

Tip of WHO

South Sudan is classified as a high-risk country in the “Eliminate Yellow Fever Outbreaks” (EYE) initiative. The epidemic spread of yellow fever is a risk in South Sudan as the estimated total population immunity is negligible, with almost 0% immunity in Kajo Keji district.

Vaccination is an essential means of preventing and controlling yellow fever and provides immunity for life. In urban centers, targeted vector control measures are also helpful in interrupting transmission. The country plans to introduce yellow fever vaccination into a routine immunization program and complete preventative mass vaccinations to accelerate the strengthening of population immunity. Accelerated planning and implementation of these population protection activities will help prevent future epidemics.

WHO recommends vaccination against yellow fever for all international travelers aged 9 months and over who travel to South Sudan, as there is evidence of persistent or periodic transmission of yellow fever virus. Yellow fever vaccination is safe, highly effective and provides lifelong protection. However, vaccination with yellow fever is not recommended for infants between the ages of 6 and 8 months, except during epidemics when the risk of transmitting the yellow fever virus is very high. The risks and benefits of vaccination in this age group should be carefully considered before vaccination. The vaccine should be used with caution during pregnancy or breastfeeding. However, pregnant women or breastfeeding women may be vaccinated during epidemics or if travel to a country or area at risk of transmission is inevitable. South Sudan requires, as a condition of entry, a valid yellow fever vaccination certificate for travelers 9 months of age and older.

In accordance with International Health Regulations (IHR 2005), Third Edition, the validity of an international vaccination certificate against yellow fever extends throughout the life of the vaccinated person. The International Vaccination Certificate becomes valid 10 days after vaccination. One dose of WHO-approved yellow fever vaccine is sufficient to provide sustained immunity and lifelong protection against yellow fever disease. No increased vaccine dose is required and international travelers are not required as a condition of entry.

The WHO encourages its Member States to take all necessary steps to ensure that passengers are well informed about the risks and preventative measures, including vaccination. As a general precaution, the WHO also recommends avoiding mosquito bites. The highest risk for yellow fever virus transmission is during the day and in the early evening. Travelers should be aware of the symptoms and signs of yellow fever and instruct them to seek medical advice quickly if they provide signs and symptoms suggestive of yellow fever infection. Travelers returning to South Sudan who may be infected with a possible high level of the virus in the blood can run the risk of establishing local yellow fever transmission cycles in areas where a competent vector is present.

WHO does not recommend any restrictions on travel and trade in the Republic of South Sudan based on information available on this epidemic.

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