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Omicron variant doesn't affect nucleic acid sensitivity
Published on: 2021-11-30
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China's current COVID-19 policy is still effective in fending off the new and more contagious variant of the coronavirus, known as Omicron, said the National Health Commission (NHC), noting that the country has established a special nucleic acid method targeting the new variant, and it is monitoring the genetic sequencing of possible imported virus cases.
 

The NHC said that the new variant does not affect the sensitivity of the country's mainstream nucleic acid testing kits. It said that the Omicron variant has more spike protein mutations, but the spike protein is not included in China's published nucleic testing kit sector.
 

Wang Guangfa, a respiratory expert at Peking University First Hospital, said that normally a nucleic acid testing kit won't cover mutations, as it will affect the test's sensitivity. As Chinese mainstream testing kits are not targeted at spike protein mutations, the new variant has no impact on the nation's current testing kits.
 

In face of the unknown danger of Omicron, Chinese pharmaceutical companies are ramping up efforts to detect the virus and tweak current vaccines.
 

Some Chinese bio-tech companies said their nucleic acid testing kits are upgraded and they are able to detect all prevailing variants, be it Delta, Gamma, Beta or Omicron.
 

The health authority said that the variant was first identified in South Africa, but that does not mean it evolved or originated from there. It noted that more information is needed to estimate the variant's transmissibility, the severity of disease and whether it can evade the immune system built by current vaccines.
 

In a technical brief on the newest "variant of concern", the World Health Organization cautioned on Monday that assessments so far were based on limited information, but said the overall global risk related to the highly mutated variant was "very high."
 

现有疫苗、核酸检测对奥密克戎有效吗?

11月29日针对新冠病毒奥密克戎变异株, 国家卫生健康委组织中国疾控中心专家就有关问题进行了解答:
 

1. 奥密克戎变异株的发现和流行情况
 

2021年11月9日,南非首次从病例样本中检测到一种新冠病毒B.1.1.529变异株。短短2周时间,该变异株即成为南非豪登省新冠感染病例的绝对优势变异株,增长迅猛。11月26日,WHO将其定义为第五种“关切变异株”(variant of concern, VOC),取名希腊字母Omicron(奥密克戎)变异株。
 

截至11月28日,南非、以色列、比利时、意大利、英国、奥地利和中国香港等,已监测到该变异株的输入。我国其他省市尚未发现该变异株的输入。奥密克戎变异株在南非首先发现和报道,但不代表这个病毒是在南非演变形成的,变异株的发现地不一定是起源地。
 

2. 奥密克戎变异株出现的可能原因
 

根据新冠病毒数据库GISAID目前共享的信息显示,新冠病毒奥密克戎变异株的突变位点数量明显多于近2年流行的所有新冠病毒变异株,尤其在病毒刺突(Spike)蛋白突变较多。
 

推测其出现的原因可能有以下三种情况:
 

(1)免疫缺陷患者感染新冠病毒后,在体内经历了较长时间的进化累积了大量突变,通过偶然机会传播;
 

(2)某种动物群体感染新冠病毒,病毒在动物群体传播过程中发生适应性进化,突变速率高于人类,随后溢出传染到人类;
 

(3)该变异株在新冠病毒基因组变异监测落后的国家或地区持续流行了很长时间,由于监测能力不足,其进化的中间代次病毒未能被及时发现。
 

3. 奥密克戎变异株的传播力
 

目前,全球尚无奥密克戎变异株传播力、致病力和免疫逃逸能力等方面的系统研究数据。但奥密克戎变异株同时具有前4个VOC变异株Alpha(阿尔法)、Beta(贝塔)、Gamma(伽玛)和Delta(德尔塔)刺突蛋白的重要氨基酸突变位点,包括增强细胞受体亲和力和病毒复制能力的突变位点。流行病学和实验室监测数据显示南非感染奥密克戎变异株病例数激增以及部分取代Delta变异株,传播力有待进一步监测研究。
 

4. 奥密克戎变异株对疫苗和抗体药物影响
 

研究表明,新冠病毒S蛋白若出现K417N、E484A或N501Y突变,提示免疫逃逸能力增强;而奥密克戎变异株同时存在“K417N+E484A+N501Y”三重突变;此外,奥密克戎变异株还存在其他多个可能降低部分单克隆抗体中和活性的突变。突变的叠加可能降低部分抗体药物对奥密克戎变异株的保护效力,对现有疫苗免疫逃逸的能力,有待进一步监测研究。
 

5. 奥密克戎变异株对我国现使用的核酸检测试剂是否有影响
 

对奥密克戎变异株的基因组分析显示,其突变位点不影响我国主流核酸检测试剂的敏感性和特异性。奥密克戎变异株突变的位点主要集中在S蛋白基因的高变异区,并不位于我国第八版《新型冠状病毒肺炎防控方案》公布的核酸检测试剂引物和探针靶标区域(中国疾控中心病毒病所向全球公布的ORF1ab基因和N基因)。但南非多个实验室的数据提示,对于检测靶标为S基因的核酸检测试剂可能无法有效检出奥密克戎变异株的S基因。

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