Neutralizing antibody titers decreased over time. The change of nAbs during the interval between last dose vaccination and blood sampling in healthy donors (a) and the time interval between disease onset and blood sampling in Delta convalescents (b). The nAbs show a sharp decline between 180 and 240 days across all VOCs and WT. In Delta convalescents, the nAbs slightly decreased within 30 days postinfection. The different colored dots represent nAbs against WT (black dots), Alpha (yellow dots), Beta (purple dots), Delta (green dots), and Omicron (red dots).