The Return of an Old Foe: A Case Series of Acute Poliomyelitis in Sabah, Malaysia

Background: Acute poliomyelitis is a disease of the anterior horn cells caused by the highly infectious poliovirus. Over recent decades, advancements in medical knowledge and vaccine development have significantly reduced the incidence of paralytic poliomyelitis worldwide, including in Malaysia. However, in October 2019, a case of poliomyelitis was reported in Tuaran, Sabah, marking the emergence of circulating vaccine-derived polioviruses (cVDPVs) in the country. This study aims to describe the clinical presentations of acute poliomyelitis caused by circulating vaccine-derived poliovirus type 1 (cVDPV1) in children. Methods: Data for this case series were obtained through a review of medical records and investigations of all children diagnosed with acute poliomyelitis during the cVDPV1 outbreak in Sabah, from October 2019 to January 2020. Results: Among six patients evaluated, four were confirmed cases of poliomyelitis, while two were classified as polio-compatible cases. All patients were male, with ages ranging from 3 months to 11 years. The majority were children of immigrants with a history of inadequate or no immunization. Fever was the most common initial symptom, followed by asymmetric flaccid paralysis. Two patients developed spinal-bulbar poliomyelitis, resulting in prolonged hospitalization. All patients experienced disabling paralysis, with one child requiring permanent ventilatory support. Poliovirus isolates from confirmed cases were identified as cVDPV1 strains, with nucleotide divergence ranging from 3.6% to 3.8%. Conclusion: The cVDPV1 poliomyelitis outbreak in Sabah underscores the severe consequences of the disease, particularly among vulnerable and socioeconomically disadvantaged populations.