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U.S. data continued to show no association between sudden sensorineural hearing loss and COVID-19 vaccines, but a population-based study in Israel hinted at something different.

Estimated incidence of hearing loss after COVID vaccination was not higher in the CDC's Vaccine Adverse Events Reporting System (VAERS) than expected from U.S. population data, according to Eric Formeister, MD, MS, of Johns Hopkins University School of Medicine in Baltimore, and co-authors reporting in .

But data from Israel, also published in , suggested a slight increased risk of sudden sensorineural hearing loss after a Pfizer-BioNTech (Comirnaty) shot. "However, the effect size is very small," reported Yoav Yanir, MD, of Lady Davis Carmel Medical Center in Haifa, and colleagues.

"Together, these two studies involving almost 200 million COVID-19 vaccine doses suggest that further investigation of the potential association between COVID-19 vaccination and sudden sensorineural hearing loss may be warranted," wrote Angela Ulrich, PhD, MPH, of the University of Minnesota in Minneapolis, and co-authors in an .

The Israeli study "reported a minimal impact with regard to public health, with sudden sensorineural hearing loss occurring in fewer than 1 per 100,000 vaccinated individuals," they added. "Neither study identified clear demographic or clinical risk factors associated with sudden sensorineural hearing loss nor did they address important measurements regarding the severity and duration of hearing loss or the clinical outcomes after treatment."

In its 2019 clinical practice guideline, the American Academy of Otolaryngology-Head and Neck Surgery estimated that sudden sensorineural hearing loss affected annually, with about 66,000 new cases a year in the U.S.

Formeister and colleagues extended a preliminary analysis of VAERS data published last year and found 555 incident reports that met the definition of probable sudden sensorineural hearing loss within 3 weeks of COVID-19 vaccination from December 2020 to July 2021, representing an annualized incidence estimate of 0.6 to 28.0 cases per 100,000 people per year. Mean patient age was 54, and 55% were women; mean time to hearing loss onset was 6 days.

Incident report rates were similar across all three vaccines: 0.16 cases per 100,000 doses for both Pfizer-BioNTech and Moderna (Spikevax) vaccines and 0.22 cases per 100,000 doses for the Johnson & Johnson vaccine.

The researchers also evaluated 21 clinical cases of confirmed sudden sensorineural hearing loss after COVID-19 vaccination. Mean time to onset was 6 days, and six of the 21 patients (28.6%) had pre-existing autoimmune disease. Of 14 patients with audiometric data after steroid treatment, eight (57.1%) experienced improvement in hearing.

"We did not find any obvious pattern in those presenting with hearing loss after vaccination -- age, gender, medical comorbidities, etc., were all what you would expect from any 'typical' presentation of idiopathic sudden sensorineural hearing loss," Formeister told 名媛直播.

In Israel, Yanir and co-authors reviewed records of 2,602,557 people in the Clalit Health Services database who received a first dose of Pfizer's COVID-19 vaccine from December 2020 through May 2021 and found 91 cases of sudden sensorineural hearing loss within 21 days of vaccination. Among 2,441,719 people who received a second vaccine dose, 79 sudden hearing loss cases were reported.

Standard incidence ratios (SIRs) weighted by age and sex were 1.35 (95% CI 1.09-1.65) after the first dose and 1.23 (95% CI 0.98-1.53) after the second. Weighted attributable risk was 0.91 excess cases per 100,000 vaccinated people after the first dose and 0.61 excess cases per 100,000 vaccinated people after the second.

After the first vaccine dose, estimated SIRs were more pronounced in 16- to 44-year-old females (SIR 1.92, 95% CI 0.98-3.43) and in females 65 or older (SIR 1.68, 95% CI 1.15-2.37). After the second dose, the highest estimated SIR was observed in males 16 to 44 years old (SIR 2.45, 95% CI 1.36-4.07).

"Considering the small effect size of this association and the good prognosis for patients with sudden sensorineural hearing loss, the potential influence of this condition on public health appears to be relatively minor," Yanir and colleagues wrote.

Both studies had important limitations. VAERS incident reports were not verified and should be interpreted with caution, Formeister and co-authors pointed out. In Israel, cases were identified by matching new diagnoses of hearing loss with concurrent prednisone treatment; people who did not receive prednisone, either because they were too late for treatment or because they had a contraindication, were not included.

"The only way to truly know if there is an association would be to perform a prospective, longitudinal cohort study in which people with and without vaccination are followed over time in order to calculate any increased risk of sudden hearing loss in those exposed to the vaccine versus those unexposed," Formeister said.