In a recent study posted to the medRxiv* preprint server, researchers investigated a potential association between coronavirus disease 2019 (COVID-19) vaccination and sudden sensorineural hearing loss (SSNHL).
Several case reports of SSNHL linked to COVID-19 vaccination have emerged during the pandemic. The European database of suspected adverse drug reaction reports lists over 1000 reports of SSNHL related to COVID-19 vaccination as of March 15, 2022. A study in Israel reported that the risk for SSNHL increased significantly after vaccination with Pfizer’s BNT162b2 vaccine.
The association of SSNHL with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection remains controversial. One study observed no apparent association between COVID-19 and SSNHL, wherein no patient with SSNHL was SARS-CoV-2-positive. Nevertheless, a few studies described the incidence of SSNHL post-infection with SARS-CoV-2.
About the study
In the present study, researchers assessed the associations of COVID-19 vaccination and SARS-CoV-2 infection with SSNHL. They examined SSNHL incidence in Finland between January 1, 2019, and April 12, 2022. A national register harboring data on birth, gender, and the unique personal identification codes of all Finnish residents, was utilized to identify all people born or alive during the study.
People diagnosed with sudden hearing loss during 2015–18 were excluded. Vaccination data were obtained from the national vaccination register and infection data from the National Infectious Disease Register. The first SARS-CoV-2-positive test result was utilized as the date of infection, and recurrent infections were not considered. The first occurrence of sudden idiopathic hearing loss after January 1, 2019, was deemed an incident SSNHL case.
Vaccination status was classified as ‘pre-epidemic non-vaccinated,’ ‘epidemic non-vaccinated,’ and ‘vaccinated.’ The vaccination status changed to ‘pre-vaccination’ for every individual 30 days before and to ‘vaccinated’ from the first vaccination date. Further, the vaccinated state was stratified into primary (≤ 54 days) and secondary (≥ 55 days) risk states. The infection status was defined as infected or non-infected.
The infection status was non-infected for the entire cohort before the COVID-19 pandemic. The infected state was stratified into primary and secondary risk periods following infection. Using a Poisson regression model, the researchers computed adjusted incidence rate ratios (aIRRs) between vaccine exposure states and the pre-epidemic non-vaccinated state and between infection exposure states and the non-infected state.
Time-invariant covariates were gender, diabetes, chronic disease count, nursing home care, cardiovascular disease, number of primary care visits, assisted living, and other institutional living. Time-independent covariates were vaccination/infection status, age groups, and calendar months. A natural spline function was utilized, accounting for the non-linear changes in the SSHNL incidence by calendar month.
In the Finnish population, the crude monthly incidence of SSNHL was variable between 2016 and 2019, from 13 to 23 per 100,000 person-years (pyrs). After 2016, the incidence was the lowest in April (11/100,000 pyrs) and May 2020 (12/100,000 pyrs) and the highest in February 2021 (27/100,000). After that, the monthly incidences were variable, similar to pre-2020. From January 2019 to pre-COVID-19, 1216 subjects experienced SSNHL with a crude incidence of 18.7 per 100,000.
A sudden decrease in SSNHL incidence was noted in the initial phase of the pandemic (March 2020) that increased to pre-COVID-19 levels by the end of 2020. The crude incidence dropped shortly after the SARS-CoV-2 vaccination program commenced in early 2021. The crude SSNHL incidences during the primary risk period following first dose administration of Oxford’s ChAdOx1, BNT162b2, and Moderna’s mRNA-1273 vaccines were 24, 20.9, and 16 per 100,000, respectively.
The aIRRs were < 1, indicating no elevated risk of SSNHL post-first vaccination. The primary and secondary risk periods post-administration of second and third doses were not significantly different than the pre-COVID-19 non-vaccinated period. Furthermore, the authors found no evidence that the risk of SSNHL increased following infection with SARS-CoV-2. The aIRRs were 1.3 and 1.1 for the primary and secondary risk periods post-infection, implying that the SSNHL incidence was not significantly different relative to the non-infected period.
The study assessed the association between SARS-CoV-2 vaccination and infection with SSNHL, comparing the incidence of SSNHL post-vaccination to that before the COVID-19 pandemic. In conclusion, there was no evidence of the suspected association of COVID-19 vaccination with SSNHL, and the aIRRs were mostly ≤ 1 during the primary risk period following vaccination.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.