A large-scale study in South Korea has found a small but notable increase in facial palsy cases within 28 days of Covid-19 vaccination, highlighting the need for post-vaccination monitoring, said the scientists.
The risk was more evident after the first and second doses of both messenger ribonucleic acid (mRNA) and viral vaccines, according to their research, which was published in Emerging Infectious Diseases Journal.
During the pandemic, vaccines were rapidly distributed, raising concerns about potential side effects, including facial palsy. Although no major safety issues emerged in clinical trials, an imbalance in cases was observed in vaccinated individuals compared with the general population.
Characterised by sudden facial muscle paralysis, the condition has been linked to infections, autoimmune reactions, and vaccination. In turn, it was prioritised as an adverse event by the Safety Platform for Emergency Vaccines (SPEAC).
Several studies investigated the association between Covid-19 vaccines and facial palsy, but their results have been inconsistent.
Differences in study population sizes, ethnicities, vaccine types, doses, and statistical methods may explain the varying outcomes. Even a systematic review and meta-analysis of these studies could not fully resolve the issue, due to limited inclusion criteria.
The inconsistent findings emphasise the need for more robust, large-scale research to reach a clear consensus on the safety of Covid-19 vaccines concerning facial palsy.
In the present study, the researchers, led by the School of Pharmacy at Sungkyunkwan University, conducted a self-controlled case series (SCCS) analysis in which they assessed the potential link.
The research was part of the Covid-19 Vaccine Safety Research Committee (CoVaSC) in South Korea. Using two large databases – the Covid-19 immunisation registry and National Health Insurance Service (NHIS) claims data – the study team identified individuals over 18 who received the vaccines between February 2021 and March 2022.
Those with missing vaccination information and prior facial palsy diagnosis were excluded.
Vaccines were classified into the following types: mRNA vaccines (BNT162b2 and mRNA-1273), viral vector vaccines (ChAdOx1 nCoV-19 and Ad26.COV2.S), and recombinant protein vaccines (NVX-CoV2373).
The SCCS design was employed to compare facial paralysis incidence during a 28-day post-vaccination risk window with a control window. Factors like age, sex, comorbidities, and insurance were considered. The primary outcome was a diagnosis of facial palsy along with a prescription for oral or parenteral corticosteroid on the same day.
The study aimed to examine vaccine types, doses, and homologous or heterologous vaccination regimens.
Statistical analysis involved the use of t-tests, chi-square tests, conditional Poisson regression, incidence rate ratios (IRRs), subgroup analyses, and Benjamini-Hochberg adjustment. Subgroup and sensitivity analyses were also conducted to ensure robustness.
Results and discussion
During the study period, 129 956 027 Covid-19 vaccine doses were administered in South Korea to 44 564 345 individuals, resulting in 15 742 cases of facial palsy with corticosteroid prescriptions.
Among these, 5 211 facial paralysis cases occurred within one to 28 days’ post-vaccination, yielding an incidence rate of 4.0 cases per million doses.
The overall risk increased within the first 28 days after vaccination (IRR 1.12). Increased risks were observed after the second dose (IRR 1.07) and when combining the first and second doses (IRR 1.08), but not after the third dose (IRR 1.01).
Both homologous and heterologous vaccinations showed increased facial palsy risks (IRR 1.14 and 1.08, respectively). mRNA vaccines had an IRR of 1.11, while viral vector vaccines had a higher risk (IRR 1.37). Sensitivity analyses confirmed the robustness of these findings across various risk windows and when excluding Covid-19 infections.
The real-world evidence provided in the study aligns with previous findings that link FP to Covid-19 vaccination.
Although the present study addressed several inconsistencies from previous studies, it is limited by potential misclassification of facial palsy cases due to reliance on the International Classification of Diseases 10th revision codes, discrepancies in the timing of occurrence and diagnosis, and possible residual confounding from undiagnosed Covid infections.
The study found a temporary increase in the risk of facial palsy after any Covid-19 vaccine dose, regardless of vaccination type or dosing.
However, the actual number of cases was small, and this risk should not deter vaccination, as FP is typically mild and manageable. Physicians are encouraged to monitor neurological signs post-vaccination and discuss the risk-benefit profile of Covid-19 vaccines with patients.
Study details
Risk for facial palsy after Covid-19 vaccination, South Korea, 2021–2022
Dongwon Yoon, Kyungyeon Jung, Ju Hwan Kim et al.
Published in CDC Emerging Infectious Diseases November 2024-10-16
Abstract
We conducted a self-controlled case series study to investigate the association between Covid-19 vaccination and facial palsy (FP) in South Korea. We used a large immunisation registry linked with the national health information database. We included 44,564,345 patients >18 years of age who received >1 dose of COVID-19 vaccine (BNT162b2, mRNA-1273, ChAdOx1 nCoV-19, or Ad.26.COV2.S) and had an FP diagnosis and corticosteroid prescription within 240 days post-vaccination. We compared FP incidence in a risk window (days 1–28) with a control window (the remainder of the 240-day observation period, excluding any risk windows). We found 5,211 patients experienced FP within the risk window and 10,531 experienced FP within the control window. FP risk increased within 28 days’post-vaccination, primarily after first and second doses and was observed for both mRNA and viral vaccines. Clinicians should carefully assess the FP risk-benefit profile associated with the Covid-19 vaccines and monitor neurologic signs after vaccination.
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