Objective To estimate the effectiveness of maternal mRNA covid-19 vaccination during pregnancy against delta and omicron severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and hospital admission in infants. Design Test negative design study. Setting Community and hospital testing in Ontario, Canada. Participants Infants younger than six months of age, born between 7 May 2021 and 31 March 2022, who were tested for SARS-CoV-2 between 7 May 2021 and 5 September 2022. Intervention Maternal mRNA covid-19 vaccination during pregnancy. Main outcome measures Laboratory confirmed delta or omicron infection or hospital admission of the infant. Multivariable logistic regression estimated vaccine effectiveness, with adjustments for clinical and sociodemographic characteristics associated with vaccination and infection. Results 8809 infants met eligibility criteria, including 99 delta cases (4365 controls) and 1501 omicron cases (4847 controls). Infant vaccine effectiveness from two maternal doses was 95% (95% confidence interval 88% to 98%) against delta infection and 97% (73% to 100%) against infant hospital admission due to delta and 45% (37% to 53%) against omicron infection and 53% (39% to 64%) against hospital admission due to omicron. Vaccine effectiveness for three doses was 73% (61% to 80%) against omicron infection and 80% (64% to 89%) against hospital admission due to omicron. Vaccine effectiveness for two doses against infant omicron infection was highest with the second dose in the third trimester (53% (42% to 62%)) compared with the first (47% (31% to 59%)) or second (37% (24% to 47%)) trimesters. Vaccine effectiveness for two doses against infant omicron infection decreased from 57% (44% to 66%) between birth and eight weeks to 40% (21% to 54%) after 16 weeks of age. Conclusions Maternal covid-19 vaccination with a second dose during pregnancy was highly effective against delta and moderately effective against omicron infection and hospital admission in infants during the first six months of life. A third vaccine dose bolstered protection against omicron. Effectiveness for two doses was highest with maternal vaccination in the third trimester, and effectiveness decreased in infants beyond eight weeks of age. The dataset from this study is held securely in coded form at ICES. While legal data sharing agreements between ICES and data providers (eg, healthcare organisations and government) prohibit ICES from making the dataset publicly available, access may be granted to those who meet pre-specified criteria for confidential access, available at (email: das{at}ices.on.ca). The full dataset creation plan and underlying analytic code are available from the authors upon request, understanding that the computer programs may rely upon coding templates or macros that are unique to ICES and are therefore either inaccessible or may require modification. Correspondence and requests for materials should be addressed to JCK.

中文翻译：

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怀孕期间母体 mRNA covid-19 疫苗接种和婴儿 delta 或 omicron 感染或入院：测试阴性设计研究

目的 评估孕期母体 mRNA covid-19 疫苗接种对 delta 和 omicron 严重急性呼吸系统综合症冠状病毒 2 (SARS-CoV-2) 感染和婴儿入院的有效性。设计测试负设计研究。在加拿大安大略省设置社区和医院检测。参与者 2021 年 5 月 7 日至 2022 年 3 月 31 日期间出生的 6 个月以下的婴儿，他们在 2021 年 5 月 7 日至 2022 年 9 月 5 日期间接受了 SARS-CoV-2 检测。干预 怀孕期间母体 mRNA covid-19 疫苗接种。主要结果指标 实验室确认的 delta 或 omicron 感染或婴儿入院。多变量逻辑回归估计疫苗有效性，并根据与疫苗接种和感染相关的临床和社会人口学特征进行调整。结果 8809 名婴儿符合资格标准，包括 99 名 delta 病例（4365 名对照）和 1501 名 omicron 病例（4847 名对照）。两次母体剂量的婴儿疫苗对 delta 感染的有效性为 95%（95% 置信区间 88% 至 98%），对因 delta 引起的婴儿入院的有效性为 97%（73% 至 100%）和 45%（37% 至 53%） ) 反对 omicron 感染，53%（39% 至 64%）反对因 omicron 入院。三剂疫苗对 omicron 感染的有效性为 73%（61% 至 80%），对因 omicron 入院的有效性为 80%（64% 至 89%）。与第一剂（47%（31% 至 59%））或第二剂（37%）相比，针对婴儿 omicron 感染的两剂疫苗有效性最高，第二剂在妊娠晚期（53%（42% 至 62%）） （24% 至 47%））三个月。两剂针对婴儿 omicron 感染的疫苗有效性从出生到 8 周之间的 57%（44% 到 66%）下降到 16 周后的 40%（21% 到 54%）。结论 母亲在怀孕期间接种第二剂 covid-19 疫苗对 delta 非常有效，对 omicron 感染和出生后前六个月婴儿入院的效果中等。第三剂疫苗加强了对 omicron 的保护。孕晚期母体接种两剂疫苗的有效性最高，八周龄以上婴儿的有效性下降。本研究的数据集以编码形式安全地保存在 ICES 中。虽然 ICES 和数据提供者之间的合法数据共享协议（例如，（电子邮件：das{at}ices.on.ca）。作者可应要求提供完整的数据集创建计划和基础分析代码，了解计算机程序可能依赖于 ICES 独有的编码模板或宏，因此无法访问或可能需要修改。信函和材料请求应发送至 JCK。