MMWR Morb Mortal Wkly Rep. 2021 Sep 3;70(35):1214-1219. doi: 10.15585/mmwr.mm7035e2.
On May 25, 2021, the Marin County Department of Public Health (MCPH) was notified by an elementary school that on May 23, an unvaccinated teacher had reported receiving a positive test result for SARS-CoV-2, the virus that causes COVID-19. The teacher reported becoming symptomatic on May 19, but continued to work for 2 days before receiving a test on May 21. On occasion during this time, the teacher read aloud unmasked to the class despite school requirements to mask while indoors. Beginning May 23, additional cases of COVID-19 were reported among other staff members, students, parents, and siblings connected to the school. To characterize the outbreak, on May 26, MCPH initiated case investigation and contact tracing that included whole genome sequencing (WGS) of available specimens. A total of 27 cases were identified, including that of the teacher. During May 23-26, among the teacher's 24 students, 22 students, all ineligible for vaccination because of age, received testing for SARS-CoV-2; 12 received positive test results. The attack rate in the two rows seated closest to the teacher's desk was 80% (eight of 10) and was 28% (four of 14) in the three back rows (Fisher's exact test; p = 0.036). During May 24-June 1, six of 18 students in a separate grade at the school, all also too young for vaccination, received positive SARS-CoV-2 test results. Eight additional cases were also identified, all in parents and siblings of students in these two grades. Among these additional cases, three were in persons fully vaccinated in accordance with CDC recommendations (1). Among the 27 total cases, 22 (81%) persons reported symptoms; the most frequently reported symptoms were fever (41%), cough (33%), headache (26%), and sore throat (26%). WGS of all 18 available specimens identified the B.1.617.2 (Delta) variant. Vaccines are effective against the Delta variant (2), but risk of transmission remains elevated among unvaccinated persons in schools without strict adherence to prevention strategies. In addition to vaccination for eligible persons, strict adherence to nonpharmaceutical prevention strategies, including masking, routine testing, facility ventilation, and staying home when symptomatic, are important to ensure safe in-person learning in schools (3).
2021 年 5 月 25 日，马林县公共卫生部（MCPH）接到一所小学的通知，称 5 月 23 日，一名未接种疫苗的教师报告新冠病毒 SARS-CoV-2 检测呈阳性。该教师报告称 5 月 19 日出现症状，但在 5 月 21 日接受检测前仍继续工作了 2 天。在此期间，尽管学校要求室内戴口罩，但该教师有时会不戴口罩向全班朗读。从 5 月 23 日开始，学校的其他教职员工、学生、家长和兄弟姐妹中报告了更多的 COVID-19 病例。为了描述疫情，5 月 26 日，MCPH 启动了病例调查和接触者追踪，包括对现有样本进行全基因组测序（WGS）。共确定了 27 例病例，其中包括该教师。在 5 月 23 日至 26 日期间，该教师的 24 名学生中，由于年龄原因未接种疫苗的 22 名学生接受了新冠病毒 SARS-CoV-2 检测；12 名学生的检测结果呈阳性。与教师课桌相邻的两排中，有 80%（10 名中的 8 名）学生呈阳性反应，而在三排后排中，有 28%（14 名中的 4 名）学生呈阳性反应（Fisher 精确检验；p = 0.036）。在 5 月 24 日至 6 月 1 日期间，学校另一年级的 6 名学生（也都因年龄太小而未接种疫苗）新冠病毒 SARS-CoV-2 检测结果呈阳性。还确定了另外 8 例病例，均为这两个年级学生的家长和兄弟姐妹。在这些额外的病例中，有 3 人按照 CDC 建议完全接种了疫苗（1）。在 27 例总病例中，有 22 例（81%）报告了症状；最常报告的症状是发烧（41%）、咳嗽（33%）、头痛（26%）和喉咙痛（26%）。对所有 18 个可用样本进行 WGS 鉴定出 B.1.617.2（Delta）变体。疫苗对 Delta 变体有效（2），但在学校中未严格遵守预防策略的未接种疫苗人群中，传播风险仍然很高。除了为符合条件的人接种疫苗外，严格遵守非药物预防策略，包括戴口罩、常规检测、设施通风以及出现症状时留在家中，对于确保学校中的面对面学习安全也很重要（3）。
