Wednesday, April 06, 2016

WHO Yellow Fever Update - Imported Cases In China

Credit CDC

*** UPDATED *** - See bottom


Ten days ago in Yellow Fever In Angola & The Risk Of International Spread - ECDC, we looked at the potential for Angola's Yellow Fever epidemic to spread to spread to other regions via viremic travelers.

Incubation is typically 3 to 6 days, and infected individuals become their most viremic just before, and during the first few days after onset of fever (cite CDC's Yellow Book) , and then are most capable of spreading the virus to others via shared mosquito bites.

The ECDC's assessment warned:

As yellow fever and dengue fever share the same mosquito vector, Aedes aegypti, any area where dengue has been transmitted could be suitable for establishment of local transmission of yellow fever if the virus is introduced by a viraemic traveller. This could be the case in southern China, where dengue virus transmission occurs during the warmer mosquito vector season, leading to local outbreaks in these areas.

Many countries (Including China) require proof of Yellow Fever vaccination for travelers arriving from countries where Yellow Fever is endemic (see WHO Country List), but it appears these requirements aren't always observed.

Today the World Health Organization reports on a total of 9 recent imported cases of Yellow Fever to China, and while the vaccination status of all of them is not known, at least 5 were not vaccinated prior to going to Angola.

Yellow Fever – China

Disease Outbreak News
6 April 2016

Between 18 March and 1 April 2016, the National IHR Focal Point of China notified WHO of 8 additional imported cases of yellow fever. 

The cases had recently returned to China from Angola. They are originally from 3 provinces in China: Fujian (6), Jiangsu (1), and Sichuan (1). The cases have a median age of 44 years (age range, 36-53 years). The majority of cases (5 cases, 62.5%) are male. The dates of symptom onset range from 5 to 17 March. Of the 8 cases, information on vaccination status is known for 5. Of these, none had received vaccination against yellow fever before going to Angola. One case did receive yellow fever vaccine in Angola, but then developed symptoms within 4 days of receiving the vaccine so is likely to have acquired the infection before protection from the vaccination could develop. 

To date, a total of 9 laboratory-confirmed yellow fever cases imported from Angola have been reported in China.

Public health response

The Chinese government has taken the following measures:
  • intensifying multi-sectoral coordination and collaboration,
  • strengthening surveillance, vector monitoring and risk assessment,
  • enhancing clinical management of yellow fever cases,
  • conducting vector control activities,
  • carrying out public risk communication activities,
  • deploying a medical team to Angola to provide yellow fever vaccination to unvaccinated Chinese nationals.

WHO risk assessment

The report of yellow fever infection in non-immunized travellers returning from a country where vaccination against the disease is mandatory underlines the need to reinforce the implementation of vaccination requirements, in accordance with the International Health Regulations (2005). Furthermore, this report highlights the risk of international spread of yellow fever through non-immunized travellers. However, the risk of establishment of a local cycle of transmission in China is low due to the current climatic condition, which is unfavourable for the competent vector, the Aedes aegypti mosquito. WHO continues to monitor the epidemiological situation and conduct risk assessment based on the latest available information.

WHO advice

WHO urges Members States especially those where the establishment of a local cycle of transmission is possible (i.e. where the competent vector is present) to strengthen the control of immunisation status of travellers to all potentially endemic areas. 

WHO does not recommend any travel or trade restriction to China based on the current information available.

The WHO has also published a report on two recently imported cases of Yellow Fever to Kenya:


Yellow Fever – Kenya

Disease Outbreak News
6 April 2016 

Between 15 and 18 March 2016, the National IHR Focal Point of Kenya notified WHO of 2 imported cases of yellow fever (YF). 

Both cases are male Kenyan nationals, in their early 30s, working in Luanda, Angola. Both travelled while symptomatic and none were vaccinated against yellow fever prior to traveling to Angola.

(Continue . . . )