Increased number of COVID-19 boosters increases the longevity of anti-RBD and anti-RBD neutralizing antibodies

Since the World Health Organization declared COVID-19 a pandemic in March 2020, the virus has caused multiple waves of infection globally. The largest four-year public university in the United States, offers a uniquely diverse setting for assessing immunity within a large community. This study aimed to evaluate SARS-CoV-2 antibody seroprevalence and the effects of infection and vaccination three years into the pandemic. A serosurvey was conducted at the public university in early 2023. Participants completed questionnaires about demographics, respiratory infection history, symptoms, and COVID-19 vaccination status. Blood samples were analyzed for anti-receptor binding domain (RBD) IgG and anti-nucleocapsid (NC) antibodies, offering a comprehensive view of immunity from both natural infection and vaccination. The seroprevalence of anti-RBD IgG antibodies was 96.2% (95% CI: 94.8%-97.2%), and 64.9% of participants had anti-NC antibodies (95% CI: 61.9%-67.8%). Anti-RBD IgG levels correlated strongly with neutralizing antibody levels, and participants who received more vaccine doses showed higher levels of both anti-RBD IgG and neutralizing antibodies. Increasing number of exposures through vaccination and/or infection resulted in higher and long-lasting antibodies. Conclusion: The high levels of anti-RBD antibodies observed reflect substantial vaccine uptake within this population. Ongoing vaccination efforts, especially as new variants emerge, are essential to maintaining antibody levels. These findings underscore the importance of sustained public health initiatives to support broad-based immunity and protection.

Methods
The study was approved by the institutional Review Board. The study population comprised students and employees recruited in early, 2021 at the University. Recruitment for this study was conducted through invitations, email announcements to the university community, and social media advertising, and potential participants were required to complete an electronic consent and a survey before giving biological specimens. The sample collection was extended for three days, in early, 2023. Participants were initially invited via emails and social media channels. Individuals were eligible for inclusion if they were 18 years of age or older and were able to provide informed consent. 999 individuals, including students and employees, who completed the screening, provided informed consent, and filled out the initial survey forms, were successfully recruited for the study. Participants were compensated for their time and efforts towards completing the survey and submitting samples.  Individuals under 18, those unable to provide consent, pregnant women, or those weighing less than 110 lbs. at the time of the survey were excluded

Demographic information, COVID-19 vaccination status, testing history, and symptoms were collected through a self-reported questionnaire. Participants voluntarily provided this information and were compensated after providing samples. Blood samples were collected by trained phlebotomists.

自2020年3月世界卫生组织（World Health Organization）宣布新型冠状病毒肺炎（COVID-19）为全球大流行以来，该病毒已在全球引发多轮感染浪潮。作为美国规模最大的四年制公立大学，其独具多样性的环境为大型社区内的免疫水平评估提供了理想场景。本研究旨在评估新冠疫情暴发三年后，严重急性呼吸综合征冠状病毒2（SARS-CoV-2）抗体的血清阳性率，以及感染与疫苗接种所产生的免疫影响。

本研究于2023年初在该公立大学开展了一项血清流行病学调查。参与者填写了涵盖人口统计学信息、呼吸道感染史、相关症状及COVID-19疫苗接种情况的调查问卷。研究人员对血液样本中的抗受体结合域（Receptor Binding Domain, RBD）免疫球蛋白G（Immunoglobulin G, IgG）与抗核衣壳（Nucleocapsid, NC）抗体进行检测，以此全面反映自然感染与疫苗接种所诱导的免疫状态。

抗RBD IgG抗体的血清阳性率为96.2%（95%置信区间（Confidence Interval, CI）：94.8%~97.2%），64.9%的参与者检出抗NC抗体（95%置信区间：61.9%~67.8%）。抗RBD IgG抗体水平与中和抗体水平呈显著正相关；接种疫苗剂次更多的参与者，其抗RBD IgG与中和抗体水平均更高。通过疫苗接种与/或自然感染获得的免疫暴露次数越多，抗体水平越高且持续时间越久。

结论：本次研究观测到的高抗RBD抗体水平，反映出该人群的疫苗接种率较高。持续推进疫苗接种工作，尤其是在新型变异株出现时，对维持抗体水平至关重要。本研究结果凸显了持续开展公共卫生举措以构建广泛免疫与防护屏障的重要性。

方法
本研究已通过机构审查委员会（Institutional Review Board, IRB）的伦理审批。研究对象为2021年初于该大学招募的学生与教职员工。本次招募通过校内邀请、面向大学社区的邮件通知以及社交媒体广告开展，潜在参与者需在提供生物样本前完成电子知情同意与调查问卷。

样本采集工作于2023年初延长至三天，参与者最初通过邮件与社交媒体渠道收到招募邀请。纳入标准为年满18周岁且能够提供知情同意的个体。最终共有999名完成筛查、签署知情同意并填写初始调查问卷的学生与教职员工成功纳入本研究。参与者因完成调查问卷与提交样本所付出的时间与精力获得相应报酬。本研究排除未满18周岁、无法提供知情同意、妊娠期女性以及调查时体重低于110磅的个体。

研究通过自填式问卷收集人口统计学信息、COVID-19疫苗接种情况、检测史及相关症状。参与者自愿提供上述信息，并在提交样本后获得报酬。血液样本由经过专业培训的采血人员采集。