Several neurological manifestations shortly after a receipt of coronavirus infectious disease 2019 (COVID-19) vaccine have been described in the recent case reports. Among those, we sought to evaluate the risk of encephalitis and meningitis after COVID-19 vaccination in the entire South Korean population. We conducted self-controlled case series (SCCS) analysis using the COVID-19 immunization record data from the Korea Disease Control Agency between February 2021 and March 2022, linked with the National Health Insurance Database between January 2021 and October 2022. We retrieved all medical claims of adults aged 18 years or older who received at least one dose of COVID-19 vaccines (BNT162b2, mRNA-1273, ChAdOx1-S, or Ad26.COV2.S), and included only those who had a diagnosis record for encephalitis or meningitis within the 240-day post-vaccination period. With day 0 defined as the date of vaccination, risk window was defined as days 1–28 and the control window as the remainder period excluding the risk windows within the 240-day period. We used conditional Poisson regression to estimate the incidence rate ratios (IRR) with 95% confidence intervals (CI), stratified by dose and vaccine type. From 129,956,027 COVID-19 vaccine doses administered to 44,564,345 individuals, there were 251 and 398 cases of encephalitis and meningitis during the risk window, corresponding to 1.9 and 3.1 cases per 1 million doses, respectively. Overall, there was an increased risk of encephalitis in the first 28 days of COVID-19 vaccination (IRR 1.26; 95% CI 1.08–1.47), which was only significant after a receipt of ChAdOx1-S (1.49; 1.03–2.15). For meningitis, no increased risk was observed after any dose of COVID-19 vaccine (IRR 1.03; 95% CI 0.91–1.16). Our findings suggest an overall increased risk of encephalitis after COVID-19 vaccination. However, the absolute risk was small and should not impede COVID-19 vaccine confidence. No significant association was found between the risk of meningitis and COVID-19 vaccination.

中文翻译：

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韩国接种 COVID-19 疫苗后发生脑炎和脑膜炎的风险：自我对照病例系列分析

最近的病例报告描述了接种 2019 年冠状病毒传染病 (COVID-19) 疫苗后不久出现的几种神经系统表现。其中，我们试图评估整个韩国人口接种 COVID-19 疫苗后患脑炎和脑膜炎的风险。我们使用韩国疾病控制局 2021 年 2 月至 2022 年 3 月期间的 COVID-19 免疫记录数据进行自我对照病例系列 (SCCS) 分析，并与 2021 年 1 月至 2022 年 10 月期间的国民健康保险数据库相链接。我们检索了所有医疗记录接受至少一剂 COVID-19 疫苗（BNT162b2、mRNA-1273、ChAdOx1-S 或 Ad26.COV2.S）的 18 岁或以上成年人的索赔，并且仅包括有脑炎诊断记录的人或疫苗接种后 240 天内发生脑膜炎。将第 0 天定义为疫苗接种日期，风险窗口定义为第 1-28 天，控制窗口定义为不包括 240 天期间风险窗口的剩余时间段。我们使用条件泊松回归来估计发病率比 (IRR)，置信区间 (CI) 为 95%，按剂量和疫苗类型分层。在向 44,564,345 人接种了 129,956,027 剂 COVID-19 疫苗中，在风险窗口内有 251 例和 398 例脑炎和脑膜炎病例，相当于每 100 万剂疫苗中分别有 1.9 例和 3.1 例。总体而言，在接种 COVID-19 疫苗后的前 28 天，脑炎风险增加（IRR 1.26；95% CI 1.08–1.47），仅在接受 ChAdOx1-S 后才显着（1.49；1.03–2.15）。对于脑膜炎，接种任何剂量的 COVID-19 疫苗后均未观察到风险增加（IRR 1.03；95% CI 0.91–1.16）。我们的研究结果表明，接种 COVID-19 疫苗后患脑炎的风险总体增加。然而，绝对风险很小，不应影响人们对 COVID-19 疫苗的信心。未发现脑膜炎风险与 COVID-19 疫苗接种之间存在显着关联。