Trends in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and vaccine antibody prevalence in a multi-ethnic inner-city antenatal population: A cross-sectional surveillance study

多民族内城区产前人群中严重急性呼吸道综合征冠状病毒 2 (SARS-CoV-2) 感染和疫苗抗体流行趋势：一项横断面监测研究