Comorbility in cases and controls of COVID-19.

Objectives
The objective of this study is to estimate the effectiveness of COVID-19 vaccines in people treated within the social security system whose vaccination status was reported to the epidemiological surveillance system.
Study design
Case-control study.
Methods
This was a case-control study conducted. The records of individuals with suspected cases of COVID-19 registered in the epidemiological surveillance system between February 1 and June 30, 2021, were studied. RT–qPCR was performed to determine SARS-CoV-2 infection; those with a positive result were considered cases, and those with a negative result were considered controls. The ratio between cases and controls was 1:1.3. The crude and adjusted vaccine effectiveness was considered the prevention of symptomatic infection and death and calculated as the difference between the dose and the risk, with a survival analysis among vaccinated people.
Results
A total of 94,416 individuals were included, of whom 40,192 were considered cases and 54,224 controls; 3,781 (4.00%) had been vaccinated against COVID-19. Vaccination also proved to be a protective factor against COVID-19, especially in the population who received a second dose (OR = 0.31; 95% CI 0.28–0.35). With the application of the vaccine, there was a protective effect against mortality (OR = 0.76; 95% CI 0.66–0.87). Disease prevention was higher for the BNT162-2 mRNA vaccine (82%) followed by the ChAdOx1 vaccine (33%). In the survival analysis, vaccination provided a protective effect.
Conclusions
There was a positive impact of vaccines for the prevention of symptomatic COVID-19, with a second dose generating greater efficacy and a reduction in deaths.

研究目标
本研究旨在评估社会保障体系内就诊、且疫苗接种信息已上报至流行病学监测系统的人群中，新冠疫苗（COVID-19 vaccine）的防护有效性。

研究设计
病例对照研究（case-control study）。

研究方法
本研究为病例对照研究，纳入2021年2月1日至6月30日期间在流行病学监测系统中登记的疑似新型冠状病毒（SARS-CoV-2）感染个体的诊疗记录。所有研究对象均接受实时荧光定量聚合酶链反应（RT-qPCR）检测以明确新型冠状病毒感染状态：检测结果呈阳性者归类为病例组，呈阴性者归类为对照组，病例组与对照组的配比比例为1:1.3。本研究将预防有症状感染与死亡作为评估终点，计算粗疫苗防护有效性与校正后疫苗防护有效性，计算公式为接种剂量相关的风险差值，并对已接种人群开展生存分析（survival analysis）。

研究结果
本研究共纳入94416名研究对象，其中病例组40192人，对照组54224人；共计3781人（占比4.00%）完成新冠疫苗接种。研究证实，疫苗接种是新冠病毒感染的保护性因素，尤其在完成第二剂接种的人群中防护效果显著（比值比（odds ratio）=0.31；95%置信区间（confidence interval）：0.28~0.35）。疫苗接种对降低死亡风险同样具有保护作用（OR=0.76；95%CI：0.66~0.87）。不同疫苗的防护效能存在差异，BNT162-2 mRNA疫苗的防护率达82%，其次为ChAdOx1疫苗（33%）。生存分析结果显示，疫苗接种可提供明确的保护效应。

研究结论
新冠疫苗对预防有症状新型冠状病毒感染具有积极作用，完成第二剂接种可进一步提升防护效果，并显著降低死亡风险。