Large-scale study in South Korea finds a small but notable increase in facial palsy cases within 28 days of COVID-19 vaccination, highlighting the need for post-vaccination monitoring.

Study: Risk for Facial Palsy after COVID-19 Vaccination, South Korea, 2021–2022. Image Credit: sruilk/Shutterstock.com

A recent study published in Emerging Infectious Diseases reported on the potential association between vaccination against coronavirus disease 2019 (COVID-19) and facial palsy (FP). They found an increased risk of FP within 28 days post-vaccination, especially after the first and second doses of both messenger ribonucleic acid (mRNA) and viral vaccines.

Background

During the COVID-19 pandemic, vaccines were rapidly distributed, raising concerns about potential side effects, including FP. Although no major safety issues emerged in clinical trials, an imbalance in FP cases was observed in vaccinated individuals compared to the general population.

FP, characterized by sudden facial muscle paralysis, has been linked to infections, autoimmune reactions, and vaccination. In turn, it was prioritized as an adverse event by the Safety Platform for Emergency Vaccines (SPEAC). Several studies investigated the association between COVID-19 vaccines and FP, 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 emphasize the need for more robust, large-scale research to reach a clear consensus on the safety of COVID-19 vaccines concerning FP. In the present study, researchers conducted a self-controlled case series (SCCS) analysis, assessing the potential link between FP and COVID-19 vaccines.

About the study

The present study was part of the COVID-19 Vaccine Safety Research Committee (CoVaSC) in South Korea. Using two large databases—the COVID-19 immunization registry and National Health Insurance Service (NHIS) claims data—researchers identified individuals above 18 years of age who received COVID-19 vaccines between February 2021 and March 2022.

Individuals with missing vaccination information and prior FP 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 FP 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 FP 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 FP with corticosteroid prescriptions. Among these, 5,211 FP cases occurred within 1–28 days post-vaccination, yielding an incidence rate of 4.0 FP cases per million doses.

The overall FP 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 FP 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 large-scale study addressed several inconsistencies from previous studies, it is limited by potential misclassification of FP cases due to reliance on the International Classification of Diseases 10^th revision codes, discrepancies in the timing of occurrence and diagnosis, and possible residual confounding from undiagnosed COVID-19 infections.

Conclusion

In conclusion, the study found a temporary increase in the risk of FP following 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.