Duration of vaccine effectiveness against each variant of concern. Points with error bars are VEs and 95% CIs of primary series and booster doses against different VOC and time since vaccination. VOC_Time includes days since the last dose vaccination during each variant of concern, - 90 means 14-90 days, - 180 means 91-180 days, and - 180 + means >= 180 days. Dotted lines were the LOESS smoothing curves, indicating VE variation tendency. Effectiveness of inactivated SARS-CoV-2 vaccines for the primary series against SARS-CoV-2 infection waned over time since vaccination and VOC and was restored by booster doses during Delta and Omicron periods; effectiveness against severe COVID-19 was much greater compared to the effectiveness against infection, improved when boosted during Delta and Omicron periods
