The Impact of Data Truncation on Rates of Vaccine-Associated Adverse Events Utilizing Open and Closed Claims: Lessons from Post-Marketing Safety Surveillance of the SARS-CoV-2 mRNA-1273 Vaccine

Background: The mRNA-1273 vaccine was granted emergency use authorization (EUA) by the FDA on 18 December 2020. Moderna implemented active safety surveillance utilizing HealthVerity open and closed claims data. Rates of adverse events (AE) among vaccinated individuals are estimated and compared to rates prior to EUA. Open claims provide near real-time data, but may incompletely capture patient activity. While closed claims capture a complete view of health services, adjudication typically requires 3-6 months.

Objectives: To understand the impact of data truncation, relative to the latest available data, when utilizing both open and closed claims on the estimated rates of AE among US adults who have received the mRNA-1273 vaccine.

Methods: The incidence rate of heart failure (HF) and acute myocardial infarction (AMI) were estimated utilizing three truncation points of cohort entry and follow-up: July 1st, 2021 (6-month truncation), October 1st, 2021 (3-month truncation), and January 10th, 2022 (no truncation). Individuals entered the cohort on a first dose of mRNA-1273 and were followed until the earliest of the AE, receipt of heterologous vaccine, closed claims disenrollment or no open claims activity within 60 days, or the truncation date.

Results: HF cases were ascertained from a population of 11,589,310 vaccinees with 6-month truncation, 13,237,868 with 3-month truncation, and 16,950,450 with no truncation, with corresponding event rates of 886.23, 777.74, and 618.24 per 100,000 person-years (PY). The percentage of HF events sourced from open claims across the 3 data truncation points was 58%, 60%, and 66%. AMI cases were ascertained from a population of 11,667,023 vaccinees with 6-month truncation, 13,324,772 with 3-month truncation, and 17,060,917 with no truncation. The incidence rates were 319.70, 301.65, and 257.57 per 100,000 PY, respectively. The percentage of AMI events sourced from open claims across the 3 data truncation points was 62%, 66%, and 74%.

Conclusions: In a real-time open and closed claims database, truncation of cohort entry and follow-up to 3 months prior to the latest available data yields incidence rates comparable to those with truncation at 6 months, suggesting that increased capture of vaccine exposures while retaining person time for follow-up can enhance the speed of safety surveillance in the setting of a mass vaccination campaign.