Peer-reviewed article
Response to a vaccine-derived poliovirus type 1 event - Sichuan, China, 2024.
Qing Yang, Jiajie Liu, Yi Liu, Xiaozhen Ma, Kai Zhang et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001In September 2024, a 4-month-old infant in Sichuan, China was diagnosed with paralytic poliomyelitis caused by a vaccine-derived poliovirus type 1 (VDPV1). Investigators found no evidence of further viral spread in contacts, the community, or wastewater. A rapid vaccination campaign in the affected county achieved high coverage rates, preventing the emergence of circulating VDPV1. Low vaccination coverage and poor sanitation were identified as contributing factors to the case.
Key points
- A 4-month-old infant developed paralytic poliomyelitis from vaccine-derived poliovirus type 1 with 10-15 nucleotide changes from the Sabin strain
- No VDPVs were detected in close contacts, healthy children, or wastewater samples
- No acute flaccid paralysis cases were found in health facilities or communities following the case
- Supplementary immunization activity achieved 95.4% coverage with bivalent live attenuated polio vaccine in children 4 months to 4 years old
- The response prevented development of circulating VDPV1, with low vaccination coverage and poor sanitation identified as risk factors
Limitations
This is a case investigation report describing the response to a single case rather than evaluating an intervention's effectiveness. The document does not provide a comparison group or long-term follow-up data to assess the sustainability of the vaccination coverage achieved.
Abstract
BACKGROUND: In September 2024, a 4-month-old infant in Liangshan, Sichuan, China was diagnosed with paralytic poliomyelitis that turned out to have been caused by a vaccine-derived poliovirus type 1 (VDPV1). This was the third VDPV outbreak detected by routine acute flaccid paralysis (AFP) surveillance in Sichuan since 2012. We conducted an epidemiological investigation into the event and implemented response measures to prevent further viral spread. METHODS: The investigation and response were conducted according to World Health Organization (WHO) and China's National Health Commission standard operating procedures. Measures included case and virus verification; search for poliovirus among contacts, healthy children, and in wastewater; active surveillance for AFP cases in health facilities and communities; vaccination coverage assessment; and supplementary immunization activity (SIA) and catch-up vaccination. RESULTS: The paralyzed infant was determined to be a VDPV1 case by the Sichuan provincial expert group; the VDPV1 had 10-15 nucleotide changes from Sabin strain type 1. No VDPVs were found in close contacts, healthy children, or wastewater; no AFP cases were found in health facilities or communities; no local circulation of the VDPV1 was detected. Following a county-wide SIA with catch-up vaccination, 2-dose, bivalent live attenuated polio vaccine coverage was 95.4% among children four months to four years of age, and full-series polio vaccine coverage was 98.5% in children 5-14 years of age. CONCLUSIONS: The VDPV was an ambiguous VDPV type 1 (aVDPV1). Timely detection and response prevented further spread and development of a circulating VDPV type 1 (cVDPV1). Low vaccination coverage and poor sanitation were contributing factors to the emergence of the aVDPV1. Information technology facilitated the strategy of "Government Locates, Health Vaccinates" that rapidly raised population immunity in a low-coverage area through a high-quality SIA and interrupted spread of the virus. CLINICAL TRIAL NUMBER: Not applicable.