Pattern of COVID-19 Epidemics in Japan Influenced by Control Measures

<b>Background.</b> COVID-19 has spread all over the world and has been around for over a year. Among the many epidemic countries, Japan differed in that avoiding the lockdowns and ask self-restraint. A huge travel campaign was carried out with a huge amount of budget, but the number of PCR tests is parsimoniously limited. These political measures may have influenced the epidemic. <b>Methods.</b> The increase or decrease in classes of SARS-CoV2 variants were estimated by analysing the published sequence with an objective multivariate analysis. This methodology does not rely on unverifiable assumptions. It observes the samples in multiple directions, digesting complex differences to be simpler forms. The results were compared over time with the numbers of confirmed cases, PCR tests, and visitors from overseas. <b>Results.</b> There have been three epidemic peaks in Japan, which were basically caused by domestically mutated variants. However, due to the relaxation of immigration [小西1] restrictions, several infective variants have come in from abroad, and they are currently competing for expansion. Among other countries, there are few other cases where multiple variants make a peak. The chaotic situation will continue for a while since currently no effort has been made to find asymptomatic carriers and details of the vaccination program is undecided. [小西1]Visiting? They will not stay long, most of them came for traveling or business.

**背景**：新型冠状病毒肺炎（COVID-19）已在全球范围内蔓延逾一年。在众多疫情流行国家中，日本的防疫策略独具特色：未实施封控措施，转而倡导民众自我约束。该国曾投入巨额预算开展大规模旅游推广活动，但新冠聚合酶链式反应（PCR）检测的开展规模却被严格限制。上述防疫政策或对本国疫情走势产生了显著影响。

**方法**：本研究通过对已公开的病毒基因组序列开展客观多变量分析，估算严重急性呼吸综合征冠状病毒2型（SARS-CoV-2）各变异株谱系的消长态势。该研究方法不依赖任何无法验证的假设，可从多维度解析样本，将复杂的序列差异简化为易于分析的形式。研究将所得结果随时间维度与确诊病例数、PCR检测量及入境境外访客数进行对比分析。

**结果**：日本先后经历三波疫情高峰，其主要诱因均为本土变异毒株。然而，由于入境管控放宽，多株具有传染性的变异毒株从境外输入，目前正处于扩增竞争阶段。在其他国家中，多变异株共同驱动疫情高峰的案例较为罕见。由于目前尚未开展无症状感染者筛查工作，且疫苗接种方案的具体细节尚未敲定，此番混乱态势或将持续一段时间。
[小西1] 入境访客？他们停留时长普遍较短，多数以旅游或商务出行为目的。