The World Health Organisation has confirmed detection of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Tanzania and Kenya.
This was disclosed in a statement released by the World Body on Friday, stating it’s highly infectious disease that largely affects children under five years of age, causing permanent paralysis (approximately 1 in 200 infections) or death (2-10% of those paralyzed).
Speaking of the one in Tanzania, the case is a child under two years old and has received three doses of bOPV vaccine, one dose of IPV for routine immunization and two doses during supplementary immunization activities (SIA) in 2022 with no documented travel history.
The child was initially reported as a case of of acute flaccid paralysis (AFP) in Rukwa region of Tanzania who experienced paralysis in late May 2023 which indicated close linkage with cVDPV2 circulating in South Kivu, Demographic Republic of the Congo (DRC).
The health authorities are conducting further field investigations including strengthening the AFP surveillance for the detection of additional AFP cases, subnational level immunity gap analysis to identify potential un-or under-immunized populations and/or areas to guide public health response activities.
WHO assessed the overall risk at the national level to be high due to sub- optimal surveillance performance in some districts, sub-optimal vaccination coverage resulting in low population immunity and the ongoing population movement across neighbouring countries.
Since 2022, Tanzania has been actively participating in a multi- country outbreak response across south-east Africa, in response to detection of different strains of poliovirus in the sub-region, including boosting immunity levels through mass vaccination campaigns and strengthening subnational surveillance capacity.
According to the WHO-UNICEF which estimated of national immunization coverage, the oral polio vaccine third dose (OPV3) and the inactivated polio vaccine first dose (IPV1) was 88% in 2022 in Tanzania.
In Kenya, on 11 July 2023, the Body received an official report regarding the detection of circulating vaccine- derived cVDPV2) was reported from Hagadera refugee camp, the second largest refugee camp in the world with over 100 000 refugees.
Four genetically-linked cVDPV2 were isolated in samples from two acute flaccid paralysis (AFP) cases, and two asymptomatic healthy children contacts, from Fafi district, Garissa county, associated with frequent population movement with neighboring Somalia.
The first case is a 2-year-old male, vaccinated with three doses of oral poliovirus vaccine (OPV), with no travel history, who developed paralysis on 26 May, and stool samples were collected on 1 June and 2 June.
The second case is a 2.7-year-old female with a travel history to Afmadhow, Lower Juba, southern Somalia, vaccinated with three doses of oral polio vaccine (OPV) who developed paralysis on 27 May, and stool samples were collected on 2 June and 3 June 2023.
The genetic sequencing analyses showed that all four isolates have undergone between 65 and 73 nucleotide changes from Sabin and are genetically linked to the cVDPV2 circulating in Banadir, Somalia.
According to the WHO UNICEF which estimates of national immunization coverage, oral polio vaccine third dose (OPV3), inactivated poliovirus vaccine first dose (IPV) was 91% in Kenya in 2021. However, coverage in Hagadera camp is 77% for both OPV3 and IPV as of May 2023.
Meanwhile, the virus is transmitted from person-to-person, mainly through the fecal-oral route or, less frequently, by a common vehicle (e.g., contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and cause paralysis.
The incubation period is usually 7-10 days but can range from 4-35 days. Up to 90% of those infected are either asymptomatic or experience mild symptoms and the disease usually goes unrecognized.