Luo Chun Huai, Morris C Paul, Sachithanandham Jaiprasath, Amadi Adannaya, Gaston David, Li Maggie, Swanson Nicholas J, Schwartz Matthew, Klein Eili Y, Pekosz Andrew, Mostafa Heba H
Johns Hopkins School of Medicine, Department of Pathology, Division of Medical Microbiology.
National Institute of Allergy and Infectious Disease, National Institutes of Health.
medRxiv. 2021 Aug 20:2021.08.15.21262077. doi: 10.1101/2021.08.15.21262077.
The emerging SARS-CoV-2 variant of concern (VOC) B.1.6.17.2 (Delta) quickly displaced the B.1.1.7 (Alpha) and is associated with increases in COVID-19 cases nationally. The Delta variant has been associated with greater transmissibility and higher viral RNA loads in both unvaccinated and fully vaccinated individuals. Data is lacking regarding the infectious virus load in Delta infected individuals and how that compares to individuals infected with other SARS-CoV-2 lineages.
Whole genome sequencing of 2,785 clinical isolates was used to characterize the prevalence of SARS-CoV-2 lineages circulating in the National Capital Region between January and July 2021. Clinical chart reviews were performed for the Delta, Alpha, and B.1.2 (a control predominant lineage prior to both VOCs) variants to evaluate disease severity and outcome and Cycle threshold values (Cts) were compared. The presence of infectious virus was determined using Vero-TMPRSS2 cells and anti-SARS-CoV-2 IgG levels were determined from upper respiratory specimen. An analysis of infection in unvaccinated and fully vaccinated populations was performed.
The Delta variant displaced the Alpha variant to constitute 88.2% of the circulating lineages in the National Capital Region by July, 2021. The Delta variant associated with increased breakthrough infections in fully vaccinated individuals that were mostly symptomatic when compared to the Alpha breakthrough infections, though it is important to note there was a significantly longer period of time between vaccination and infection with Delta infections. The recovery of infectious virus on cell culture was significantly higher with the Delta variant compared to Alpha in both vaccinated and unvaccinated groups. The impact of vaccination on reducing the recovery of infectious virus from clinical samples was only observed with Alpha variant infections but was strongly associated with low localized SARS-CoV-2 IgG for both variants. A comparison of Ct values showed a significant decrease in the Delta compared to Alpha with no significant differences between unvaccinated and vaccinated groups.
Our data indicate that the Delta variant is associated with increased infectious virus loads when compared to the Alpha variant and decreased upper respiratory antiviral IgG levels. Measures to reduce transmission in addition to increasing vaccinations rates have to be implemented to reduce Delta variant spread.
NIH/NIAID Center of Excellence in Influenza Research and Surveillance contract HHS N2772201400007C, Johns Hopkins University, Maryland department of health, Centers for Disease Control and Prevention contract 75D30121C11061.
新出现的严重急性呼吸综合征冠状病毒2（SARS-CoV-2）变异株B.1.617.2（德尔塔）迅速取代了B.1.1.7（阿尔法），并在全国范围内与新冠肺炎病例增加有关。德尔塔变异株在未接种疫苗和完全接种疫苗的个体中都具有更强的传播性和更高的病毒RNA载量。目前缺乏关于德尔塔感染个体中传染性病毒载量的数据，以及与感染其他SARS-CoV-2谱系个体的比较情况。
对2785份临床分离株进行全基因组测序，以确定2021年1月至7月在国家首都地区流行的SARS-CoV-2谱系的流行情况。对德尔塔、阿尔法和B.1.2（两种变异株出现之前的主要对照谱系）变异株进行临床图表回顾，以评估疾病严重程度和转归，并比较循环阈值（Ct）值。使用Vero-TMPRSS2细胞确定传染性病毒的存在，并从呼吸道标本中测定抗SARS-CoV-2 IgG水平。对未接种疫苗和完全接种疫苗人群的感染情况进行分析。
到2021年7月，德尔塔变异株取代了阿尔法变异株，在国家首都地区的流行谱系中占88.2%。德尔塔变异株与完全接种疫苗个体中突破性感染增加有关，与阿尔法突破性感染相比，这些感染大多有症状，不过需要注意的是，接种疫苗和德尔塔感染之间的时间间隔明显更长。在接种疫苗和未接种疫苗的组中，与阿尔法变异株相比，德尔塔变异株在细胞培养上传染性病毒的回收率显著更高。仅在阿尔法变异株感染中观察到接种疫苗对降低临床样本中传染性病毒回收率的影响，但两种变异株均与低水平局部SARS-CoV-2 IgG密切相关。Ct值比较显示，与阿尔法变异株相比，德尔塔变异株的Ct值显著降低，未接种疫苗和接种疫苗组之间无显著差异。
我们的数据表明，与阿尔法变异株相比，德尔塔变异株与传染性病毒载量增加以及呼吸道抗病毒IgG水平降低有关。除了提高疫苗接种率外，还必须采取措施减少传播，以减少德尔塔变异株的传播。
美国国立卫生研究院/美国国立过敏和传染病研究所流感研究与监测卓越中心合同HHS N2772201400007C、约翰霍普金斯大学、马里兰州卫生部、疾病控制和预防中心合同75D30121C11061。
