A study in Emerging Infectious Diseases explores the association between COVID-19 vaccination and facial palsy (FP) in South Korea. The authors use an immunisation registry linked to the national health information database to compare FP incidence in a risk window with a control window. They found an increased FP risk within 28 postvaccination, primarily after first and second doses of both mRNA and viral vaccines. They encourage clinicians to “carefully assess” the FP risk-benefit profile associated with COVID-19 vaccines and monitor neurologic signs after vaccination.
Risk of facial palsy
Although no severe safety concerns were observed during the clinical trials of COVID-19 vaccines, an “imbalance” in facial palsy (FP) incidence after vaccination was identified in vaccinated persons compared to the general population. The aetiology of FP “remains elusive”, but autoimmune mechanisms or vaccination are “considered potential contributors to its development”. FP is included in the priority list of adverse events of special interest generated by the Safety Platform for Emergency vACcines (SPEAC) because of its “sudden and acute symptom onset”.
Despite multiple studies on the association of FP with COVID-19, we lack a “clear consensus”. As these studies have produced “controversial and inconclusive results”, the authors identified a need to generate an “in-depth body of evidence and a clear consensus” on the subject.
The study
The study uses two large, linked databases in South Korea to conduct a self-controlled case series analysis. It is intended to provide evidence on the safety of COVID-19 vaccines for immunisation under the COVID-19 Vaccine Safety Research Committee (CoVaSC) in South Korea. Several vaccines were available during the study period in South Korea:
- BNT162b2 (Pfizer-BioNTech)
- mRNA-1273 (Moderna)
- ChAdOx1 nCoV-19 (AstraZeneca)
- Ad.26.COV2.S (Janssen)
- NVX-CoV2373 (Novavax)
The researchers identified persons aged 18 and older who received an initial COVID-19 vaccine dose between 26th February 2021 and 1st March 2022. Among this population, they identified and included patients with a primary FP diagnosis accompanied by a prescription for corticosteroids between 26th February 2021 and 31st October 2022; patients who had received a COVID-19 vaccination and had incident FP diagnosed within a prespecified observation period were also included.
Exclusion criteria included foreign born residents, participants in clinical trials, persons vaccinated abroad, and persons deviating from vaccination guidelines to account for potential exposure misclassification. Persons with a history of FP in the year preceding the observation period and those whose FP cases occurred after the end of the observation period were excluded.
44,564,345 persons in South Korea were administered 129,956,027 COVID-19 vaccines doses between 26th February 2021 and 1st March 2022. During the study period, 15,472 FP cases with corticosteroid prescriptions were identified. Among these, 5,211 occurred up to 28 days postvaccination: 4.0 GP cases/1 million doses. Among the FP study population, the mean age at first COVID-19 vaccination was 53.1 years. 54.7% were male and 45.3% were female.
The study showed FP risk increased within 1-28 days after any COVID-19 vaccine dose. Increased FP risks were observed with the second dose and combined first and second doses, but no association was found for the third dose. The increased FP risk was identified across vaccine types. The incidence rate ratios (IRR) were “generally consistent” across age groups and, after application of the Benjamini-Hochberg adjustment, “generally remained consistent” across sex.
Implications
The findings of this study add to growing evidence of a positive association between FP and COVID-19 vaccination. The exact biological mechanism for the development of FP after vaccination remains unknown. However, “plausible links” between FP and mRNA and viral vector vaccines have been proposed. The study revealed increased FP risk in persons homologously vaccinated with mRNA vaccines, especially for BNT162b2 and in those with at least a single dose of mRNA vaccine. Furthermore, it revealed elevated risks among patients who received homologous dosing of viral vector vaccines.
An important consideration is the suggested link between COVID-19 infection itself and FP onset. In South Korea, the annual incidence of Bell’s palsy increased from 23.0 to 30.8 cases per 100,000 persons from 2008 and 2018. It reached 32.5 cases per 100,000 persons during 2021-2022, which suggests an increasing trend during the pandemic. Additionally, a study in South Korea indicated that COVID-19 infection is associated with a higher risk for Bell’s palsy for both COVID-19 vaccine recipients and nonrecipients.
“In conclusion, our study revealed a transient risk for FP after any dose of COVID-19 vaccine.”
The authors note that, although the risk for FP “appears elevated”, the absolute number of cases was “small”. Risk for FP should therefore not discourage patients from receiving COVID-19 vaccinations.
“Because FP is generally mild and manageable, physicians should monitor neurologic signs after COVID-19 vaccination and provide patients with a comprehensive evaluation of the risk-benefit profile associated with COVID-19 vaccines.”
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