Sudden hearing loss following vaccination against COVID-19

Importance Spontaneous adverse reaction reports of sudden hearing loss have been observed and a population-based cohort study conducted in Israel showed an increase in the incidence of sudden sensorineural hearing loss (SSNHL) following vaccination with messenger RNA COVID-19 vaccine BNT162b2 (Pfizer-BioNTech). However, in this setting, possibility of confounding remained. Objective To assess a potential association between COVID-19 vaccinations and SSNHL. Design A register-based country-wide observational study with study period from January 1, 2019, until Apr 12, 2022. Setting Residents in Finland: 5,8 million. Participants All individuals identified from population information system alive or born during the study period except individuals having SSNHL during 2015 to 2018 according to specialized care derived diagnosis codes for SSNHL (ICD10-code H91.2) as a primary or secondary diagnosis. Exposures The a priori primary risk period was 0 to 54 days following each COVID-19 vaccine dose. The secondary risk time was 55 or more days after the vaccination. A later vaccine exposure overruled a previous one. A secondary analysis included a risk time of 0 to 54 days following a positive polymerase chain reaction (PCR) test for SARS-CoV-2. Main Outcome We compared incidences of SSNHL following COVID-19 vaccination to incidences before the COVID-19 epidemic in Finland. In our Poisson regression analysis, we adjusted for calendar time, age, sex, diabetes, cardiovascular disease, other chronic diseases, number of visits in primary health care. Results Comparison time constituted of 6.5 million person years, primary risk time of 1.7 million person years, and secondary risk time of 2.1 million person years. Before the epidemic yearly 18.7 / 100,000 people were diagnosed with SSNHL. Our data suggested no increased risk for SSNHL following any COVID-19 vaccination. In particular, adjusted incidence rate ratios, with 95 percent confidence intervals (95% CI) for the BNT162b2 vaccine’s three doses were 0.8 (95% CI 0.6 to 1.0), 0.9 (95% CI 0.6 to 1.2), and 1.3 (95% CI 0.9 to 2.0). SARS-CoV-2 infection was not associated with an increased incidence of SSNHL either. Conclusions and relevance Our results show no evidence of increased SSNHL with the COVID-19 vaccinations. We accounted for previous disease and other potential confounding factors. Our results base on diagnosis codes in specialized care but still need to be verified with settings, that are capable to evaluate the degree of hearing loss. Key Points Question Are COVID-19 vaccinations associated with sudden sensorineural hearing loss (SSNHL), when assessed in a register-based country-wide observational study with data on potential confounding factors? Findings Our data suggested no increased risk for SSNHL following any COVID-19 vaccination. Meaning A large previous cohort study shows an increased risk for SSNHL following vaccine BNT162b2 (Pfizer-BioNTech) – our results, that take pre-existing disease into account, demonstrate no such an effect.