Ravindran Saranyah, Gubbay Jonathan B, Cronin Kirby, Sullivan Ashleigh, Zygmunt Austin, Johnson Karen, Buchan Sarah A, Parpia Alyssa S
Health Protection, Public Health Ontario, Toronto, Ontario, Canada.
Public Health Ontario Laboratory, Public Health Ontario, Toronto, Ontario, Canada.
Open Forum Infect Dis. 2023 May 22;10(6):ofad282. doi: 10.1093/ofid/ofad282. eCollection 2023 Jun.
Increased immune evasion by emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and occurrence of breakthrough infections raise questions about whether coronavirus disease 2019 vaccination status affects SARS-CoV-2 viral load among those infected. This study examined the relationship between cycle threshold (Ct) value, which is inversely associated with viral load, and vaccination status at the onset of the Omicron wave onset in Ontario, Canada.
Using linked provincial databases, we compared median Ct values across vaccination status among polymerase chain reaction-confirmed Omicron variant SARS-CoV-2 cases (sublineages B.1.1.529, BA.1, and BA.1.1) between 6 and 30 December 2021. Cases were presumed to be Omicron based on S-gene target failure. We estimated the relationship between vaccination status and Ct values using multiple linear regression, adjusting for age group, sex, and symptom status.
Of the 27 029 presumed Omicron cases in Ontario, the majority were in individuals who had received a complete vaccine series (87.7%), followed by unvaccinated individuals (8.1%), and those who had received a booster dose (4.2%). The median Ct value for post-booster dose individuals (18.3 [interquartile range, 15.4-22.3]) was significantly higher than that for unvaccinated (17.9 [15.2-21.6]; = .02) and post-vaccine series individuals (17.8 [15.3-21.5]; = .005). Post-booster dose cases remained associated with a significantly higher median Ct value than cases in unvaccinated individuals ( ≤ .001), after adjustment for covariates. Compared with values in persons aged 18-29 years, Ct values were significantly lower among most age groups >50 years.
While slightly lower Ct values were observed among unvaccinated individuals infected with Omicron compared with post-booster dose cases, further research is required to determine whether a significant difference in secondary transmission exists between these groups.
新型严重急性呼吸综合征冠状病毒2（SARS-CoV-2）变体免疫逃逸能力增强以及突破性感染的出现，引发了关于2019冠状病毒病疫苗接种状况是否会影响感染者体内SARS-CoV-2病毒载量的疑问。本研究调查了在加拿大安大略省奥密克戎毒株流行初期，与病毒载量呈负相关的循环阈值（Ct）值和疫苗接种状况之间的关系。
利用省级关联数据库，我们比较了2021年12月6日至30日期间聚合酶链反应确诊的奥密克戎变体SARS-CoV-2病例（谱系B.1.1.529、BA.1和BA.1.1）不同疫苗接种状况下的Ct值中位数。根据S基因靶点缺失推测病例为奥密克戎毒株。我们使用多元线性回归估计疫苗接种状况与Ct值之间的关系，并对年龄组、性别和症状状况进行了调整。
在安大略省27029例推测为奥密克戎毒株的病例中，大多数是已完成全程疫苗接种的个体（87.7%），其次是未接种疫苗的个体（8.1%）和接种了加强针的个体（4.2%）。接种加强针个体的Ct值中位数（18.3[四分位间距，15.4 - 22.3]）显著高于未接种疫苗个体（17.9[15.2 - 21.6]；P = 0.02）和完成疫苗接种系列个体（17.8[15.3 - 21.5]；P = 0.005）。在调整协变量后，接种加强针的病例Ct值中位数仍显著高于未接种疫苗个体的病例（P≤0.001）。与18 - 29岁人群的值相比，大多数50岁以上年龄组的Ct值显著更低。
虽然与接种加强针的病例相比，感染奥密克戎毒株的未接种疫苗个体的Ct值略低，但需要进一步研究以确定这些组之间在二次传播方面是否存在显著差异。
