[Source: World Health Organization, Weekly Epidemiological Record, full PDF document: (LINK). Edited.]

Weekly epidemiological record / Relevé épidémiologique hebdomadaire, 16 AUGUST 2013, 88th year / 16 AOÛT 2013, 88e année, No. 33, 2013, 88, 349–356 - http://www.who.int/wer


Poliomyelitis outbreak in Somalia and Kenya, 2013


On 9 May 2013, the Ministry of Health of Somalia reported a confirmed case of poliomyelitis due to type 1 wild poliovirus (WPV1) in a girl aged 32 months from Mogadishu with onset of acute flaccid paralysis (AFP) on 18 April 2013. A week later, on 16 May 2013, Kenya confirmed a case of WPV1 in a girl aged 4 months from the Dadaab refugee camp in North Eastern Province of Kenya with date of onset of AFP on 30 April 2013. This report updates the initial report of 14 June 2013 and describes the epidemiology of the outbreak and the response measures that have been put in place.(1)

In recent years, there has been an overall decrease in the number of WPV exportations to non-endemic countries. In 2010, importation of WPV into 16 non-endemic countries resulted in 1120 cases of poliomyelitis, accounting for 83% of all WPV cases globally.(2) In 2011, in addition to small outbreaks following importation of type 3 WPV (WPV3) into 4 West African countries and WPV1 importation into the Central African Republic, one large WPV1 polio outbreak occurred in China, resulting in 21 cases of paralytic poliomyelitis.(3)

In 2012, there was only one reported importation of WPV, from Nigeria to Niger, causing a single paralytic case; all other WPV cases occurred in the 3 polioendemic countries (Afghanistan, Nigeria and Pakistan), and in Chad where WPV transmission had been re-established.

Historically, Somalia successfully stopped the transmission of indigenous WPV in 2002. However, in 2005 Somalia experienced an outbreak that resulted in 228 reported cases of poliomyelitis. After a series of outbreak response vaccination campaigns, the outbreak was terminated in March 2007. During the past 10 years, Kenya has experienced 3 outbreaks following importation of WPV, the first in 2006 which resulted in 2 cases, a second in 2009 which resulted in 19 cases, and a third in 2011 which resulted in a single case of paralytic poliomyelitis.(3)

Outbreak epidemiology

As of 31 July 2013, 95 confirmed WPV1 cases had been reported in Somalia and 10 cases in Kenya (…). Of the 95 cases in Somalia, 20 (21%) were reported in children aged <12 months, 33 (35%) in children aged 12–23 months, 35 (37%) in children aged 2–4 years, 7 (7%) in children aged 5–15 years; no cases have been reported in individuals aged >15 years.

Nearly half (44%) of cases reported having never been vaccinated with the oral poliovirus vaccine (OPV), 22 (23%) reported having had 1–3 doses of OPV, and 31 (33%) reported having received ≥4 OPV doses; 56 of the cases (59%) were reported in males. Of the 95 cases, 55 (58%) were reported from the Banadir Province where the index case was reported, and 20 (21%) of the cases were reported from the Lower Shabelle Province.

Of the 10 cases reported from Kenya, epidemiological information was available for 8 cases. Of these 8 cases, 1 was reported in an infant 12 months of age, none in children aged 12–23 months, 3 in children aged 2–4 ears, none in children aged 5–15 years, and 4 in adults (2 aged 19 years and one aged 22). Four of the cases reported having never been vaccinated with OPV, 2 reported having had 1–3 doses of OPV, and 2 reported having received ≥4 OPV doses; 3 of the cases were reported in males. In Kenya, all of the cases reported from the North Eastern Province (Map 1). Of the 8 cases in Kenya with information available, 7 were reported among Somali refugees and one was reported in a child living in the host community.

On 14 August 2013, the Kenya Medical Research Institute (KEMRI) issued an advanced notification of a case of WPV1 from a child living in Ethiopia with date of onset 10 July 2013. The case is from the Somali Province of Ethiopia in a child aged 18 months who had never been vaccinated with OPV. Investigation of this prospective case is ongoing.

The results from the genetic sequence analysis of the WPV isolates from Somalia and Kenya confirm that the viruses in Somalia and Kenya are closely related.

This finding suggests that the outbreak is a result of a single or simultaneous introduction of wild virus into the region followed by local circulation and spread. The imported viruses are closely related to WPV1 strains that were recently isolated in West Africa.

Outbreak response and control efforts

To intensify surveillance, steps have been taken to enhance reporting of AFP cases in both Somalia and Kenya. Active surveillance for AFP has been intensified in reporting sites and all health facilities and informers have been alerted to the need for immediate case reporting. Active case searches are also being conducted as part of the house-to-house vaccination response.


Following the initial notification of the index case on 9 May 2013, the first supplementary immunization activity (SIA) in Somalia was conducted from 14 to 18 May 2013 in multiple districts of Benadir using the trivalent oral poliovirus vaccine (tOPV). In one high-risk district the target age group was increased to 10 years.

During an SIA, OPV is administered to all children aged <5 years regardless of previous vaccination history. However, in order to strengthen the outbreak response and optimize population immunity, during this outbreak response an intensified strategy has been adopted. In some areas of Somalia, the target age group was expanded to include older children such as all children <10 years of age and in some areas all age groups were included.

Four additional short-interval SIAs have been conducted in Somalia (28 May–2 June, 12–18 June, 1–6 July and 21–25 July 2013) including 3 nationwide campaigns using bivalent OPV (bOPV). Two of these campaigns have included all age groups in Benadir and other South and Central regions. In order to immunize mobile populations and prevent further spread of the outbreak, special transit vaccination posts have been established at main transit points and in congregation points.


In Kenya, the first SIA was conducted from 27 to 31 May 2013 among children aged <15 years in the refugee camps and 3 surrounding host districts using bOPV and tOPV. Two additional SIAs have been conducted in Kenya (17–21 June and 1–10 July 2013) using bOPV. These campaigns targeted 1.35 million and 4.5 million individuals in 22 and 123 districts respectively, and the target age group was expanded to all ages <15 years in some of the highest risk areas.

International response

In addition to Somalia and Kenya, internationally coordinated outbreak response immunization activities have been conducted in Ethiopia (5–8 June and 21 June–1 July 2013) and in Yemen (2–4 June and 30 June–2 July 2013) to reduce the risk of spread and outbreaks across the Horn of Africa.


The current outbreak in the Horn of Africa is likely to be large, of long duration, and to spread rapidly. For the past 3 years, immunization activities in some regions of Somalia have been significantly constrained by ongoing conflict and insecurity. Over time, this has led to the build-up of a large susceptible population of children. At the beginning of the outbreak it was estimated that around 600 000 children <5 years of age were living in areas that had not been reached for the past 3 years by large scale-immunization activities. Furthermore, throughout the first 2 months of the outbreak response, conflict has continued to limit the reach of vaccination teams. Joint WHO and UNICEF estimates indicate that the coverage of 3 doses of OPV through routine immunization in Somalia in 2012 was only 47%, indicating the presence of a large cohort of susceptible children in the country.(4)

The detection of WPV in both South-Central and North Somalia and Eastern Kenya, and most likely in the Somali Province of Ethiopia, shows that transmission has extended over large geographical distances. During the large international polio outbreak in 2005, multiple countries in the Horn of Africa were affected including Eritrea, Ethiopia, Kenya, Somalia and Yemen, resulting in >700 cases of paralytic poliomyelitis. Therefore, the Global Polio Eradication Initiative (GPEI) is creating localized plans to maximize opportunities to vaccinate children in areas where access is limited by conflict and insecurity.

Globally, this is the first reported large-scale WPV outbreak since the WPV1 outbreak that was reported in China in August 2011. It demonstrates the ongoing threat of WPV spread to polio-free countries that will persist until WPV transmission is stopped in the remaining endemic countries. The risk of a large and explosive outbreak following introduction of WPV is much higher in areas affected by prolonged conflict and complex humanitarian emergencies where there are large cohorts of susceptible children. But despite protracted conflict spanning decades, the programme in Somalia has been successful in stopping transmission of indigenous WPV in 2002 and subsequently was able to stop transmission in 2007 during the large multicountry polio outbreak in the Horn of Africa. This experience indicates that with a strong and wellcoordinated response it is feasible to terminate the current WPV outbreak in Somalia.

The outbreak responses in Somalia and Kenya have been exceptionally rapid and intensive. Notably, special strategies have been employed to limit transmission and spread of WPV such as short-interval, expanded age group campaigns, mostly using the bOPV which is more efficacious against WPV1 than the trivalent OPV. The first SIA in Somalia was conducted within 6 days after notification of the first WPV case. International collaboration for the outbreak response has enabled outbreak-affected and at-risk countries to synchronize and coordinate their efforts in order to strengthen the overall impact of the response.

Ongoing insecurity is a continuing challenge to the quality of the campaigns being conducted in Somalia. For this reason, vaccination posts have been set up at key transit points to immunize hard-to-reach populations. The involvement of communities, their leaders and local authorities in conflict-affected and insecure areas is essential to maximize the opportunities to vaccinate all children in Somalia. Efforts are ongoing to ensure that the support of all local stakeholders is aligned and the polio outbreak is rapidly brought under control in all areas of Somalia.

The global polio eradication programme continues to make strong progress in the 3 remaining polio-endemic countries. The recently launched Polio Eradication and Endgame Strategic Plan 2013–2018,5 includes contingency planning for dealing with outbreaks in polio-free areas until all WPV transmission has ceased in endemic countries. The expected duration, extent and the public health impact of this outbreak necessitate planning for an extended and intensive outbreak response. While international financing will be critical for an effective public health emergency response, the success of the response will depend largely on the commitment of governments, local authorities, and vaccinators.

The WHO manual International Travel and Health(6) recommends that all travellers to and from polioaffected areas be fully vaccinated against poliomyelitis. This includes the 3 countries which remain endemic for indigenous transmission of WPV (Afghanistan, Nigeria and Pakistan) and countries in the Horn of Africa where WPV has recently been re-introduced (Kenya and Somalia).

The Ministry of Health in Saudi Arabia has issued the Health Regulations for travellers for the 2013 Hajj which, as in previous years, includes requirements for polio vaccination. These regulations state that visitors of all ages travelling to Saudi Arabia from polioendemic countries, as well as recently endemic, and re-established transmission countries (Afghanistan, Chad, India, Kenya, Nigeria, Pakistan, and Somalia) should be vaccinated against poliomyelitis with OPV and must provide proof of vaccination prior to applying for a visa. Irrespective of previous immunization history, all visitors arriving in Saudi Arabia will also receive 1 dose of OPV upon arrival. All visitors aged <15 years travelling from countries reporting polio following importation or due to circulating vaccinederived poliovirus in the past 12 months (Niger and Yemen) should be vaccinated against poliomyelitis with OPV; proof of vaccination with OPV or an inactivated poliovirus vaccine is required with visa applications. Irrespective of previous immunization history, all visitors aged <15 years arriving in Saudi Arabia will also receive 1 dose of OPV upon arrival.(7)
  1. See No. 24, 2013, pp. 241–242.
  2. See No. 12, 2012, pp. 109–115.
  3. See data (as of 23 July 2013) from WHO headquarters on wild poliovirus for 2008–2013. Available from http://www.polioeradication.org/Portals/0/Document/Data&Monitoring/Wild_poliovirus_list_2008_2013_23Jul.pdf ; accessed August 2013.
  4. WHO vaccine-preventable diseases: monitoring system, 2013 global summary. Data for Somalia as of 12 July 2013. Available from http://apps.who.int/immunization_monitoring/globalsummary, accessed August 2013.
  5. Available from http://www.polioeradication.org/Portals/0/Document/Resources/StrategyWork/GPEI_Plan_FactFile_EN.pdf , accessed August 2013
  6. See http://www.who.int/ith/en/
  7. Voir N° 32, 2013, pp. 327-331.