During July 2021, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.617.2 variant infections, including vaccine breakthrough infections, occurred after large public gatherings in Provincetown, Massachusetts, USA, prompting a multistate investigation. Public health departments identified primary and secondary cases by using coronavirus disease surveillance data, case investigations, and contact tracing. A primary case was defined as SARS-CoV-2 detected <14 days after travel to or residence in Provincetown during July 3–17. A secondary case was defined as SARS-CoV-2 detected <14 days after close contact with a person who had a primary case but without travel to or residence in Provincetown during July 3–August 10. We identified 1,098 primary cases and 30 secondary cases associated with 26 primary cases among fully and non–fully vaccinated persons. Large gatherings can have widespread effects on SARS-CoV-2 transmission, and fully vaccinated persons should take precautions, such as masking, to prevent SARS-CoV-2 transmission, particularly during substantial or high transmission.

2021 年 7 月，美国马萨诸塞州普罗温斯敦发生大型公众集会后，发生了严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) B.1.617.2 变异感染，包括疫苗突破性感染，引发了多州调查。公共卫生部门通过使用冠状病毒疾病监测数据、病例调查和接触者追踪来识别原发性和继发性病例。原发病例被定义为7 月 3 日至 17 日期间前往普罗温斯敦或居住在普罗温斯敦后 14 天内检测到的 SARS-CoV-2。继发病例被定义为与原发病例密切接触但在 7 月 3 日至 8 月 10 日期间没有前往或居住在普罗温斯敦的人密切接触后 14 天内检测到的 SARS-CoV-2。我们发现了 1,098 例原发病例和 30 例继发病例与完全和未完全接种疫苗的人中的 26 例原发病例相关。大型集会可能对 SARS-CoV-2 传播产生广泛影响，完全接种疫苗的人应采取预防措施（例如遮盖口罩），以防止 SARS-CoV-2 传播，特别是在大量传播或高传播期间。