Kenya

Status: affected by circulating vaccine-derived poliovirus

Circulation of vaccine-derived poliovirus type 2 (cVDPV2) has been confirmed in the Horn of Africa, with the same strain confirmed in Kenya and Somalia. No cases of acute flaccid paralysis (AFP) associated with this cVDPV2 have been detected at this time – the viruses were all isolated from environmental samples. Surveillance for AFP cases in the area is being strengthened.

In Somalia, three VDPV2s were isolated from environmental samples collected 4 and 11 January 2018, from Hamarweyn district in Banadir province (Mogadishu). These isolates are genetically linked to previously isolated VDPV2s from 2017, collected on 22 October and 2 November 2017 from environmental samples collected from Waberi district, Banadir province.

In Kenya, one cVDPV2 was isolated from an environmental sample collected on 21 March 2018 from Nairobi, linked to the cVDPV2 previously confirmed in Somalia.

Since detection of the initial isolates in 2017, outbreak response campaigns in line with internationally-agreed guidelines have been implemented, consisting of three large-scale immunization activities (SIAs) in Banadir, Lower Shabelle and Middle Shabelle provinces in Somalia, with further campaigns planned for April and May.

With detection of the virus in Nairobi, indicating a regional event, the possibility of a region-wide response is now being evaluated. The exact scale and extent of the response is being finalized. WHO and its partners are continuing to support local public health authorities in conducting field investigations and risk assessments to more clearly assess any potential risk of circulation of the identified cVDPV2, and to continue to support the outbreak response and strengthening of disease surveillance.

Health personnel at all levels are undertaking efforts to strengthen surveillance for acute flaccid paralysis (AFP) cases, including by conducting active case searches. The frequency of sampling from the environment is being increased.

Somalia and Kenya conducted their last immunization campaigns with trivalent OPV in early 2016, in advance of the trivalent to bivalent OPV switch in April 2016. Searches for residual trivalent OPV stocks are ongoing including public, private and NGOs. No tOPV stocks have been found.

Neighbouring countries across the Horn of Africa, including in Yemen, have been alerted, and public health authorities are assessing overall immunity levels and strengthening disease surveillance in those countries.

The detection of cVDPV2 underscores the importance of maintaining high levels of routine vaccination coverage at all levels to minimize the risk and consequences of any poliovirus circulation. Such events also underscore the risk in areas or regions with continued substantial insecurity that hampers maintaining high population immunity through routine vaccination. A robust outbreak response is needed to rapidly stop the VDPV2 transmission. WHO will continue to evaluate the epidemiological situation and outbreak response measures being implemented.

Polio this week in Horn of Africa

  • The Horn of Africa is currently affected by separate outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2) and type 3 (cVDPV3), reporting both cases and environmental positives.
  • One new case of cVDPV3 was reported in the past week, from Middle Shabelle, Somalia, with onset of paralysis on 7 September.
  • The country is carrying out outbreak response to both virus types in line with internationally-agreed guidelines. An Outbreak Response Assessment is due to start on 18 November, followed by a Technical Advisory Group meeting.
  • Read our Somalia country page and Kenya country page to see information on surveillance and vaccination campaigns.
  • Learn more about vaccine-derived polioviruses through this short animation or this ‘Coffee with Polio Experts’ video.

International Health Regulations

Kenya is classified by the International Health Regulations (IHR) as a state infected with cVDPV2, with potential risk of international spread. It is therefore subject to temporary recommendations as of August 2018.

Travel advice

WHO’s International Travel and Health recommends that all travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or inactivated polio vaccine (IPV) within 4 weeks to 12 months of travel.

More on vaccine-derived polioviruses