Response to Letter to the Editor

Dear Professor Marianna Hagan, Dr. Hinpetch Daungsupawong, and Dr. Viroj Wiwanitkit We really appreciate your valuable suggestions and beneficial comments, and we would like to reply to the points that you mentioned. The first concern is the sample sizes in each time period. In this study, we retrospectively analyzed clinical data of all patients who visited our hospital in July of every year before COVID-19 pandemic (2019), during COVID-19 pandemic (2020), and after inactivated vaccination (2021). Our study included 4,225 patients before COVID-19, 3,322 patients during COVID-19, and 5,432 patients after vaccination and valuated the Sudden Sensorineural Hearing Loss (SSNHL) of the periods. The relationship between COVID-19 and SSNHL has been one of the hot points after the outbreak of COVID-19. In 2021, a study from an Italian audiology tertiary referral center included 2,761 in the pandemic year period, 3,446 in the first precedent year period, and 3,407 in the second precedent year period, respectively, to explore SSNHL and vestibular disorders during and before COVID-19 pandemic (1). Also in 2021, a study from China included 4,662, 3,986, 4,791, and 5,274 patients separately in 2017, 2018, 2019, and 2020 to analyze the characteristics of patients in the department of otolaryngology during the COVID-19 pandemic (2). In 2021, a study from America studied the impact of COVID-19 on presentation of SSNHL by analyzing a total of 4,013 patients in one period of 2019 (3). Therefore, although we included every July in 2019 to 2021, because of the large population base of our country and the large hospital admissions, and compared to the previous reports on the sudden sensorineural hearing loss (SSNHL) before and during the COVID-19 epidemic, we consider the sample sizes in our study were relatively large and could convincingly support our conclusions. The other concern is the bias of retrospective design of the study. Compared to some other epidemiological methods, such as randomized control trial (RCT), the retrospective design belongs to observational study, and certain natural bias is inevitable. To adjust confounding variables, the most frequently used methods include enlarging the sample sizes, extracting the patients’ information in the same way, and using matched controls. In our study, we selected the same months of year 2019 to 2021, which was also in consistent with the principle of extracting the patients’ information in the same way to eliminate the confounding variables. As we mentioned above, the sample was relatively large, which could adjust the confounding variables to the large extent. As a tertiary referral center, the professionals and doctors of our department had all been strictly trained, so the diagnose criteria and treatment for SSNHL in our department are normalized and standard, which is in accordance to the SSNHL guidelines and which could also eliminate the confounding variables to the large extent. Lastly, as you suggested, we will conduct a prospective study and focus on the long-term follow-up of the SSNHL patients occurred during COVID-19 pandemic. Once again, thank you for all the valuable suggestions. Warm regards, Juanjuan Gao Haijin Yi Juanjuan GaoHaijin YiDepartment of Otolaryngology Head and Neck Surgery Beijing Tsinghua Changgung Hospital School of Clinical Medicine Tsinghua University, Beijing, China E-mail: [email protected]