Abstract
This study aimed to explore the dynamic trends and determinants of COVID-19 vaccine hesitancy among adults in China from 2021 to 2022, providing evidence for targeted vaccination strategies under different epidemic control phases. We conducted four large-scale, anonymous, cross-sectional online surveys in January 2021, June 2021, January 2022, and June 2022. Adults aged 18 and older were recruited nationwide, with demographic weighting based on the 2020 National Census. Vaccine hesitancy was defined according to WHO SAGE guidelines. Multilevel regression and post-stratification (MRP) were applied to estimate standardized provincial-level vaccine hesitancy rates, and multilevel logistic models were used to examine influencing factors, including sociodemographic characteristics and constructs from the health belief model (HBM). Adjusted vaccine hesitancy rates showed a U-shaped trend: 33.78% in January 2021, dropping to 11.33% in June 2021, rising slightly to 16.13% in January 2022, and rebounding to 31.72% in June 2022. Hesitancy was initially driven by concerns over vaccine safety, while later stages reflected reduced risk perception and vaccination fatigue. Younger adults, women, urban residents, and those with higher education levels were more likely to exhibit hesitancy. HBM factors - particularly perceived safety and effectiveness - were significant early drivers but diminished in influence over time. Vaccine hesitancy among Chinese adults fluctuated with changes in pandemic context and public perception, shifting from safety concerns to complacency. Sustained public health efforts are needed to address psychological, social, and contextual barriers to vaccination, especially in later phases of epidemic control. Tailored strategies based on population subgroups and behavioral insights are essential to mitigate hesitancy and maintain high vaccination coverage.