Emerg Infect Dis. 2022 Feb;28(2):331-337. doi: 10.3201/eid2802.211789. Epub 2021 Dec 7.
We developed a case-case study to compare mRNA vaccine effectiveness against Delta versus Alpha coronavirus variants. We used data on 2,097 case-patients with PCR-positive severe acute respiratory syndrome coronavirus 2 infections reported in Portugal during May-July 2021. We estimated the odds of vaccine breakthrough infection in Delta-infected versus Alpha-infected patients by using conditional logistic regression adjusted for age group and sex and matched by the week of diagnosis. We compared reverse-transcription PCR cycle threshold values by vaccination status and variant as an indirect measure of viral load. We found significantly higher odds of vaccine breakthrough infection in Delta-infected patients than in Alpha-infected patients (odds ratio 1.96 [95% CI 1.22-3.14]), suggesting lower effectiveness of the mRNA vaccines in preventing infection with the Delta variant. We estimated lower mean cycle threshold values for the Delta cases (mean difference -2.10 [95% CI -2.74 to -1.47]), suggesting higher infectiousness than the Alpha variant.
我们开展了一项病例对照研究，以比较 mRNA 疫苗对德尔塔和阿尔法变异株的有效性。我们使用了 2097 例 2021 年 5 月至 7 月期间在葡萄牙报告的 PCR 阳性严重急性呼吸综合征冠状病毒 2 感染的病例患者数据。我们通过调整年龄组和性别并按诊断周进行匹配的条件逻辑回归，估计了德尔塔感染患者与阿尔法感染患者之间疫苗突破性感染的几率。我们比较了按疫苗接种状态和变异株划分的逆转录 PCR 循环阈值值，作为病毒载量的间接衡量标准。我们发现德尔塔感染患者的疫苗突破性感染几率显著高于阿尔法感染患者（比值比 1.96 [95%置信区间 1.22-3.14]），表明 mRNA 疫苗在预防德尔塔变异株感染方面的效果较低。我们估计德尔塔病例的平均循环阈值值较低（平均差异-2.10 [95%置信区间-2.74 至-1.47]），表明其传染性高于阿尔法变异株。
