(247) Background Incidence Rates of Adverse Events of Special Interest for SARS-CoV-2 Vaccines Safety Monitoring in the US

Publication Number: 1292

Background: Understanding the safety profile of a new vaccine in the post-marketing period is essential to public health. Generation of robust background incidence rates of potential Adverse Events of Special Interest (AESI) is important for identification of vaccine safety signals post launch.

Objectives: To quantify annual background incidence rates of 60 AESI among an unvaccinated population before and during the COVID-19 pandemic and in subpopulations of interest: i) pregnant women, ii) pediatric population ( < 18 years), iii) elderly population (≥65 years), and iv) among influenza vaccine recipients (to contextualize future AESI analyses among patients who receive COVID-19 vaccine).

Methods: We conducted a population-based retrospective cohort study using Optum Clinformatics Data Mart, a large US-based administrative claims database. We estimated annual background incidence rates of various cardiac, gastrointestinal, neurologic, dermatologic, endocrine, hematologic, immunologic, renal and respiratory AESI in a general population and in subpopulations. Analyses were conducted in two time periods: in a pre-COVID-19 era (Jan. 1, 2017 to Dec. 31, 2019) and in a COVID-19 era prior to COVID-19 vaccine introduction (Mar. 1, 2020 to Dec. 31, 2020) to capture shifting societal and healthcare system practices during a time in which SARS-CoV-2 infections were prevalent.

Results: The average annual study population was approximately 16 million, with a slightly larger percentage of females than males. AESI rates were generally stable, with some variations across the study years and between the pre-COVID-19 and COVID-19 eras. For select AESI, the annual AESI rates per 100,000 person years (95% confidence interval) in 2019 and in 2020 among the general population were, respectively: 16.8 (15.9, 17.7) and 23.7 (22.5, 24.9) for myocarditis, 45.4 (44.0, 46.8) and 41.8 (40.2, 43.3) for pericarditis, 5.7 (5.2, 6.3) and 4.6 (4.1, 5.1) for single organ cutaneous vasculitis, 9.0 (8.4, 9.6) and 7.5 (6.8, 8.1) for subacute thyroiditis, 186.1 (183.2, 189.0) and 206.3 (202.9, 209.7) for thrombotic thrombocytopenia syndrome, 3.7 (3.3, 4.1) and 3.0 (2.6, 3.4) for Guillain-Barré Syndrome (including Miller-Fisher syndrome), and 2.6 (2.3, 2.9) and 2.4 (2.1, 2.8) for acute disseminated encephalomyelitis. Similar trends were observed among influenza vaccine recipients across both eras, with slightly elevated rates compared to the general population.

Conclusions: This study estimated background rates for a large number of AESI in time periods with and without SARS-CoV-2 circulation, before vaccine introduction. Findings from this study may be used to monitor or study AESI during post-marketing safety surveillance for COVID-19 vaccines and other vaccines.