Background: Vaccine-associated paralytic poliomyelitis (VAPP) and immunodeficient long-term polio excretors\nconstitute a significant public health burden and are a major concern for the WHO global polio eradication\nendgame.\nCase presentation: Poliovirus type 3 characterized as Sabin-like was isolated from a 5-month-old Albanian child\nwith X-linked agammaglobulinemia and VAPP after oral polio vaccine administration. Diagnostic workup and\ntreatment were performed in Italy. Poliovirus replicated in the gut for 7 months. The 5� non coding region (NCR),\nVP1, VP3 capsid proteins and the 3D polymerase genomic regions of sequential isolates were sequenced. Increasing\naccumulation of nucleotide mutations in the VP1 region was detected over time, reaching 1.0 % of genome\nvariation with respect to the Sabin reference strain, which is the threshold that defines a vaccine-derived poliovirus\n(VDPV). We identified mutations in the 5�NCR and VP3 regions that are associated with reversion to neurovirulence.\nDespite this, all isolates were characterized as Sabin-like. Several amino acid mutations were identified in the VP1\nregion, probably involved in growth adaptation and viral persistence in the human gut. Intertypic recombination\nwith Sabin type 2 polio in the 3D polymerase region, possibly associated with increased virus transmissibility, was\nfound in all isolates. Gamma-globulin replacement therapy led to viral clearance and neurological improvement,\npreventing the occurrence of persistent immunodeficiency-related VDPV.\nConclusions: This is the first case of VAPP in an immunodeficient child detected in Albania through the Acute\nFlaccid Paralysis surveillance system and the first investigated case of vaccine associated poliomyelitis in Italy since\nthe introduction of an all-Salk schedule in 2002. We discuss over the biological and clinical implications in the\ncontext of the Global Polio Eradication Program and emphasize on the importance of the Acute Flaccid Paralysis\nsurveillance.
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