Prevalence of SARS-CoV-2 antibodies among Belgian nursing home residents and staff during the primary COVID-19 vaccination campaign

Nursing home residents (NHR) and staff have been disproportionally affected by the COVID-19 pandemic and were therefore prioritised in the COVID-19 vaccination strategy. However, frail older adults, like NHR, are known to have decreased antibody responses upon vaccination targeting other viral antigens. As real-world data on vaccine responsiveness, we assessed the prevalence of SARS-CoV-2 antibodies among Belgian NHR and staff during the primary COVID-19 vaccination campaign. In total, we tested 1629 NHR and 1356 staff across 69 Belgian NHs for the presence of SARS-CoV-2 IgM/IgG antibodies using rapid tests. We collected socio-demographic and COVID-19-related medical data through questionnaires. Sampling occurred between 1 February and 24 March 2021, in a randomly sampled population that received none, one or two BNT162b2 vaccine doses. We found that during the primary vaccination campaign with 59% of the study population fully vaccinated, 74% had SARS-CoV-2 antibodies. Among fully vaccinated individuals only, fewer residents tested positive for SARS-CoV-2 antibodies (77%) than staff (98%), suggesting an impaired vaccine-induced antibody response in the elderly, with lowest seroprevalences observed among infection naïve residents. COVID-19 vaccination status and previous SARS-CoV-2 infection were predictors for SARS-CoV-2 seropositivity. Alternatively, age ≥ 80 years old, the presence of comorbidities and high care dependency predicted SARS-CoV-2 seronegativity in NHR. These findings highlight the need for further monitoring of SARS-CoV-2 immunity upon vaccination in the elderly population, as their impaired humoral responses could imply insufficient protection against COVID-19. This study was retrospectively registered on ClinicalTrials.gov (NCT04738695).

养老院居民（Nursing Home Residents, NHR）与工作人员在新冠疫情中受到的影响远超普通人群，因此被纳入新冠疫苗接种策略的优先接种范畴。然而，诸如养老院居民这类体弱老年群体，已知在针对其他病毒抗原的疫苗接种后，其抗体应答水平会出现显著下降。本研究作为疫苗应答性的真实世界数据来源，于比利时新冠疫苗基础免疫接种活动期间，评估了当地69家养老院的1629名居民与1356名工作人员体内新型冠状病毒（SARS-CoV-2）抗体的流行率。研究团队采用快速检测手段，对上述人群的SARS-CoV-2 IgM/IgG抗体进行了检测，并通过问卷收集了受试者的社会人口学特征与新冠相关临床数据。本次采样工作开展于2021年2月1日至3月24日，采样人群为随机招募的、未接种、接种1剂或2剂BNT162b2疫苗的个体。研究结果显示，在本次基础免疫接种活动期间，本研究队列中有59%的受试者完成了全程疫苗接种，整体人群中74%的个体检测出新型冠状病毒抗体。仅在完成全程接种的人群中，养老院居民的抗体阳性率（77%）显著低于工作人员（98%），提示老年人群的疫苗诱导抗体应答能力受损；其中未感染过新冠的居民血清阳性率最低。新冠疫苗接种状态与既往新型冠状病毒感染史是新型冠状病毒血清阳性的独立预测因素。而在养老院居民群体中，年龄≥80岁、合并基础疾病以及高护理依赖程度则是新型冠状病毒血清阴性的预测因素。本研究结果提示，需进一步加强对老年人群接种疫苗后的新型冠状病毒免疫状态监测，因为该群体受损的体液免疫应答可能意味着其对新冠病毒的防护不足。本研究已在ClinicalTrials.gov平台完成回顾性注册，注册号为NCT04738695。