Notes from the Field: Readiness for use of type 2 novel oral poliovirus vaccine in response to a type 2 circulating vaccine-derived poliovirus outbreak--Tajikistan, 2020-2021/Notes du terrain: Preparation a l'utilisation du nouveau vaccin antipoliomyelitique oral de type 2 en reponse a une flambee epidemique de poliovirus circulants derives d'une souche vaccinale de type 2 Tadjikistan, 2020-2021.

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From: Weekly Epidemiological Record(Vol. 97, Issue 13)
Publisher: World Health Organization
Document Type: Article
Length: 2,550 words
Lexile Measure: 1780L

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On 13 January 2021, a vaccine-derived poliovirus type 2 (VDPV2) was identified by the Regional Reference Laboratory (RRL) for polio in Moscow (1) in a specimen from a patient with acute flaccid paralysis (AFP) in Jaloliddin Balkhi district, Khatlon Region, Tajikistan. Paralysis onset occurred on 22 November 2020. On 6 February 2021, a second, genetically linked VDPV2 paralytic case, with onset of paralysis on 17 January 2021, was confirmed in Khatlon Region in the neighbouring Vakhsh district, indicating local transmission. Genetic sequencing of the isolate by the RRL showed a 20-nucleotide divergence from Sabin vaccine virus strain and a 14-nucleotide divergence from a circulating VDPV2 (cVDPV2) reported from Khikorgangi, Pakistan on 7 December 2020, suggesting undetected circulation for approximately 12 months. (2) High-quality AFP surveillance in Tajikistan indicated that these cases were probably recent importations. (3) During 2014, the Director-General of WHO declared polio a Public Health Emergency of International Concern under the International Health Regulations (2005), isolation of any poliovirus requiring immediate reporting and prompt response. (4)

Children born after global cessation of use of type 2-containing oral poliovirus vaccine (OPV) in routine immunization schedules in April 2016 have no mucosal immunity against type 2 polioviruses. Therefore, cVDPV2 outbreak immunization responses require the use of type 2-containing OPVs; however, in low-coverage settings, use of type 2 oral poliovirus vaccine increases the risk of seeding (5) new cVDPV2 emergences. (2,6) Current type 2-containing poliovirus vaccines are Sabin strain monovalent type oral poliovirus vaccine (mOPV2) and trivalent oral poliovirus vaccine (tOPV); tOPV is preferred where there is co-circulation of WPV1 and cVDPV2. To mitigate new seeding events, WHO granted emergency use listing (EUL) of a recently developed, genetically stabilized, novel OPV type 2 (nOPV2) during November 2020. The Tajik Ministry of Health and Social Protection of the Population, in consultation with partners, conducted a rigorous risk assessment and determined that nOPV2 was the best vaccine for outbreak response and would protect the polio-free status of the WHO European Region. The Ministry of Health completed and documented the 25 EUL readiness criteria for the initial use phase (7) for vaccine release in 8 weeks, which was then authorized by the WHO Director-General, making Tajikistan the first country outside the WHO African Region to use nOPV2. (8) The Ministry incorporated nOPV2 into 3 rounds of outbreak response, including supplementary immunization activities (SIAs) (Figure 1). The targeted age group for rounds 1 and 2 was children aged 0-65 months, and that for round 3 was children aged 0-55 months.

A total of 31 cVDPV2 cases were confirmed between 22 November and 26 June 2021, none of which occurred after the second SIA; virus was also isolated from close contacts of AFP cases, in community stool collection surveys and from environmental samples. (9) The geographical spread of cVDPV2 comprised 10 districts in Khatlon Region and a broad central belt that included Dushanbe, the capital. The first outbreak response assessment was conducted during 16-20 August 2021, and an additional nOPV2 SIA was recommended at the end...

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Gale Document Number: GALE|A699771543