Incidence rates of thrombosis with thrombocytopenia syndrome (TTS) among adults in United States commercial and Medicare claims databases, 2017–2020

•Annual TTS IRs were similar between Jan-Dec 2019 and Jan-Oct 2020.•Common site TTS IRs increased with age and were higher among males.•Unusual site TTS IRs were higher in males than females.•Unusual site TTS IRs increased with age for adults aged 18–64 years.•For adults aged ≥ 65 years, unusual site TTS IRs decreased with age. Increased risk of thrombosis with thrombocytopenia syndrome (TTS) following adenovirus vector-based COVID-19 vaccinations has been identified in passive surveillance systems. TTS incidence rates (IRs) in the United States (U.S.) are needed to contextualize reports following COVID-19 vaccination. We estimated annual and monthly IRs of overall TTS, common site TTS, and unusual site TTS for adults aged 18–64 years in Carelon Research and MarketScan commercial claims (2017–Oct 2020), CVS Health and Optum commercial claims (2019–Oct 2020), and adults aged ≥ 65 years using CMS Medicare claims (2019–Oct 2020); IRs were stratified by age, sex, and race/ethnicity (CMS Medicare). Across data sources, annual IRs for overall TTS were similar between Jan-Dec 2019 and Jan-Oct 2020. Rates were higher in Medicare (IRs: 370.72 and 365.63 per 100,000 person-years for 2019 and 2020, respectively) than commercial data sources (MarketScan IRs: 24.21 and 24.06 per 100,000 person-years; Optum IRs: 32.60 and 31.29 per 100,000 person-years; Carelon Research IRs: 24.46 and 26.16 per 100,000 person-years; CVS Health IRs: 30.31 and 30.25 per 100,000 person-years). Across years and databases, common site TTS IRs increased with age and were higher among males. Among adults aged ≥ 65 years, the common site TTS IR was highest among non-Hispanic black adults. Annual unusual site TTS IRs ranged between 2.02 and 3.04 (commercial) and 12.49 (Medicare) per 100,000 person-years for Jan-Dec 2019; IRs ranged between 1.53 and 2.67 (commercial) and 11.57 (Medicare) per 100,000 person-years for Jan-Oct 2020. Unusual site TTS IRs were higher in males and increased with age in commercial data sources; among adults aged ≥ 65 years, IRs decreased with age and were highest among non-Hispanic American Indian/Alaska native adults. TTS IRs were generally similar across years, higher for males, and increased with age. These rates may contribute to surveillance of post-vaccination TTS.