Nikbakht Fateme, Heidarian Miri Hamid, Mosafarkhani Ehsan, Sharifjafari Fatemeh, Taghipour Ali
Department of Epidemiology, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran.
School of Nursing and Midwifery, University College Cork, Cork, Ireland.
PLoS One. 2025 Mar 26;20(3):e0317959. doi: 10.1371/journal.pone.0317959. eCollection 2025.
COVID-19 has rapidly spread around the world, and the duration of protective immunity against the virus remains unknown. Evidence suggests that patients with a confirmed COVID-19 infection may experience reinfection. The aim of this study is to determine the relationship between COVID-19 reinfection and previous infection history in the population covered by Mashhad University of Medical Sciences.
This population-based, historical cohort study included all individuals with health records at the health service centers of Mashhad University of Medical Sciences who underwent PCR testing during the study period (April 1, 2020, up to February 19, 2022). The data were analyzed by calculating the infection rate in both PCR-positive and negative individuals, and estimating the adjusted rate ratio using Poisson regression.
The results of this study in the entire population showed that the incidence rate in people with a history of primary COVID-19 infection was 13% higher than that in people who had no history of this disease. However, in the group that received the vaccine prior to the first PCR test, the incidence rate was lower among individuals with a positive first test result (IRR = 0.71) compared to those with a negative first test result.
The study reveals that prior COVID-19 infection does not ensure immunity and may increase the risk of reinfection, particularly among men and younger individuals. Vaccination appears to complicate this dynamic, as those with multiple vaccine doses showed higher reinfection rates compared to those with fewer doses. These findings highlight the need for ongoing research and tailored public health strategies to address the complexities of COVID-19 immunity and reinfection.
新冠病毒病（COVID-19）已在全球迅速传播，针对该病毒的保护性免疫持续时间尚不清楚。有证据表明，确诊感染COVID-19的患者可能会再次感染。本研究的目的是确定在马什哈德医科大学覆盖的人群中，COVID-19再次感染与既往感染史之间的关系。
这项基于人群的历史性队列研究纳入了在马什哈德医科大学健康服务中心有健康记录且在研究期间（2020年4月1日至2022年2月19日）接受PCR检测的所有个体。通过计算PCR检测阳性和阴性个体的感染率，并使用泊松回归估计调整后的率比来分析数据。
该研究在整个人群中的结果显示，有COVID-19初次感染史的人群发病率比无该病病史的人群高13%。然而，在首次PCR检测前接种过疫苗的组中，首次检测结果为阳性的个体发病率低于首次检测结果为阴性的个体（发病率比=0.71）。
该研究表明，既往COVID-19感染并不能确保免疫，反而可能增加再次感染的风险，尤其是在男性和年轻人中。接种疫苗似乎使这种动态情况变得复杂，因为接种多剂疫苗的人群与接种较少剂次的人群相比，再次感染率更高。这些发现凸显了持续开展研究和制定针对性公共卫生策略以应对COVID-19免疫和再次感染复杂性的必要性。
