The coronavirus disease 2019 (COVID-19) pandemic has affected the world radically since 2020. Spain was one of the European countries with the highest incidence during the first wave. As a part of a consortium to monitor and study the evolution of the epidemic, we sequenced 2,170 samples, diagnosed mostly before lockdown measures. Here, we identified at least 500 introductions from multiple international sources and documented the early rise of two dominant Spanish epidemic clades (SECs), probably amplified by superspreading events. Both SECs were related closely to the initial Asian variants of SARS-CoV-2 and spread widely across Spain. We inferred a substantial reduction in the effective reproductive number of both SECs due to public-health interventions (R_e < 1), also reflected in the replacement of SECs by a new variant over the summer of 2020. In summary, we reveal a notable difference in the initial genetic makeup of SARS-CoV-2 in Spain compared with other European countries and show evidence to support the effectiveness of lockdown measures in controlling virus spread, even for the most successful genetic variants.

自 2020 年以来，2019 年冠状病毒病 (COVID-19) 大流行对世界产生了根本性影响。西班牙是第一波发病率最高的欧洲国家之一。作为监测和研究流行病演变的联盟的一部分，我们对 2,170 个样本进行了测序，这些样本大多在封锁措施之前得到诊断。在这里，我们确定了至少 500 个来自多个国际来源的介绍，并记录了两个主要西班牙流行病进化枝 (SEC) 的早期兴起，这可能被超级传播事件放大了。这两种 SEC 都与 SARS-CoV-2 的最初亚洲变种密切相关，并在西班牙广泛传播。我们推断，由于公共卫生干预，两个 SEC 的有效繁殖数量都会大幅减少 ( R _e < 1)，也反映在 2020 年夏季 SEC 被新变体取代。总而言之，我们揭示了西班牙与其他欧洲国家相比 SARS-CoV-2 初始基因组成的显着差异，并展示了证据支持封锁措施在控制病毒传播方面的有效性，即使对于最成功的基因变异也是如此。