Background

Vaccine effectiveness studies have not differentiated the effect of the delta (B.1.617.2) variant and potential waning immunity in observed reductions in effectiveness against SARS-CoV-2 infections. We aimed to evaluate overall and variant-specific effectiveness of BNT162b2 (tozinameran, Pfizer–BioNTech) against SARS-CoV-2 infections and COVID-19-related hospital admissions by time since vaccination among members of a large US health-care system.

Methods

In this retrospective cohort study, we analysed electronic health records of individuals (≥12 years) who were members of the health-care organisation Kaiser Permanente Southern California (CA, USA), to assess BNT162b2 vaccine effectiveness against SARS-CoV-2 infections and COVID-19-related hospital admissions for up to 6 months. Participants were required to have 1 year or more previous membership of the organisation. Outcomes comprised SARS-CoV-2 PCR-positive tests and COVID-19-related hospital admissions. Effectiveness calculations were based on hazard ratios from adjusted Cox models. This study was registered with ClinicalTrials.gov, NCT04848584.

Findings

Between Dec 14, 2020, and Aug 8, 2021, of 4 920 549 individuals assessed for eligibility, we included 3 436 957 (median age 45 years [IQR 29–61]; 1 799 395 [52·4%] female and 1 637 394 [47·6%] male). For fully vaccinated individuals, effectiveness against SARS-CoV-2 infections was 73% (95% CI 72–74) and against COVID-19-related hospital admissions was 90% (89–92). Effectiveness against infections declined from 88% (95% CI 86–89) during the first month after full vaccination to 47% (43–51) after 5 months. Among sequenced infections, vaccine effectiveness against infections of the delta variant was high during the first month after full vaccination (93% [95% CI 85–97]) but declined to 53% [39–65] after 4 months. Effectiveness against other (non-delta) variants the first month after full vaccination was also high at 97% (95% CI 95–99), but waned to 67% (45–80) at 4–5 months. Vaccine effectiveness against hospital admissions for infections with the delta variant for all ages was high overall (93% [95% CI 84–96]) up to 6 months.

Interpretation

Our results provide support for high effectiveness of BNT162b2 against hospital admissions up until around 6 months after being fully vaccinated, even in the face of widespread dissemination of the delta variant. Reduction in vaccine effectiveness against SARS-CoV-2 infections over time is probably primarily due to waning immunity with time rather than the delta variant escaping vaccine protection.

Funding

Pfizer.

中文翻译：

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mRNA BNT162b2 COVID-19 疫苗在美国大型综合卫生系统中的有效性长达 6 个月：一项回顾性队列研究

 背景

疫苗有效性研究尚未区分 delta (B.1.617.2) 变体的影响和观察到的针对 SARS-CoV-2 感染的有效性降低中潜在的免疫力减弱的影响。我们的目的是按美国大型医疗保健系统成员接种疫苗以来的时间，评估 BNT162b2（tozinameran，辉瑞-BioNTech）对 SARS-CoV-2 感染和与 COVID-19 相关的住院治疗的整体和变异特异性有效性。

 方法

在这项回顾性队列研究中，我们分析了南加州 Kaiser Permanente 医疗保健组织（美国加利福尼亚州）成员的个人（≥12 岁）的电子健康记录，以评估 BNT162b2 疫苗针对 SARS-CoV-2 感染的有效性，以及与 COVID-19 相关的住院治疗最长 6 个月。参与者必须拥有该组织一年或以上的会员资格。结果包括 SARS-CoV-2 PCR 阳性检测和与 COVID-19 相关的入院情况。有效性计算基于调整后的 Cox 模型的风险比。本研究已在 ClinicalTrials.gov 注册，NCT04848584。

 发现

2020 年 12 月 14 日至 2021 年 8 月 8 日期间，我们对 4 920 549 名接受资格评估的个人进行了评估，其中包括 3 436 957 名（中位年龄 45 岁 [IQR 29–61]）；1 799 395 名女性 [52·4%] 和 1 名女性637 394 [47·6%] 男性）。对于完全接种疫苗的个体，针对 SARS-CoV-2 感染的有效性为 73% (95% CI 72-74)，针对与 COVID-19 相关的住院治疗的有效性为 90% (89-92)。抗感染的有效性从全面接种疫苗后第一个月的 88% (95% CI 86-89) 下降到 5 个月后的 47% (43-51)。在测序感染中，疫苗对 delta 变体感染的有效性在全面疫苗接种后的第一个月内较高（93% [95% CI 85–97]），但 4 个月后下降至 53% [39–65]。全面接种疫苗后第一个月针对其他（非 delta）变异的有效性也高达 97%（95% CI 95-99），但在 4-5 个月时下降至 67%（45-80）。对于所有年龄段的 delta 变体感染，疫苗在 6 个月内的总体有效性均较高（93% [95% CI 84-96]）。

 解释

我们的结果支持 BNT162b2 在完全接种疫苗后约 6 个月内对住院的高效性，即使面对 delta 变种的广泛传播也是如此。随着时间的推移，疫苗针对 SARS-CoV-2 感染的有效性降低可能主要是由于免疫力随着时间的推移而减弱，而不是由于 Delta 变体逃脱了疫苗的保护。

 资金

 辉瑞。