Applying two approaches to detect unmeasured confounding due to time-varying variables in a self-controlled risk interval design evaluating COVID-19 vaccine safety signals, using myocarditis as a case example.

We test the robustness of the self-controlled risk interval (SCRI) design in a setting where time between doses may introduce time-varying confounding, using both negative control outcomes (NCOs) and quantitative bias analysis (QBA). All vaccinated cases identified from 5 European databases between 1 September 2020 and end of data availability were included. Exposures were doses 1-3 of the Pfizer, Moderna, AstraZeneca, and Janssen COVID-19 vaccines; outcomes were myocarditis and otitis externa (NCO). The SCRI used a 60-day control window and dose-specific 28-day risk windows, stratified by vaccine brand and adjusted for calendar time. The QBA included two scenarios: (i) baseline probability of the confounder was higher in the control window and (ii) vice versa. The NCO was not associated with any of the COVID-19 vaccine types or doses except Moderna dose 1 (IRR = 1.09, 95%CI 1.01-1.09). The QBA suggested even the strongest literature-reported confounder (COVID-19; RRmyocarditis = 18.3) could only explain away part of the observed effect from IRR = 3 to IRR = 1.40. The SCRI seems robust to unmeasured confounding in the COVID-19 setting, although a strong unmeasured confounder could bias the observed effect upward. Replication of our findings for other safety signals would strengthen this conclusion.

Risk of herpes zoster in adults with SARS-CoV-2 infection in Spain: A population-based, retrospective cohort study.

OBJECTIVES: We aimed to compare the risk of herpes zoster (HZ) in adults with and without laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. METHODS: This retrospective dynamic cohort study analyzed data from a public healthcare database in Spain between November 2020 and October 2021. The main outcome was incident cases of HZ in individuals ≥18-year-old. Relative risk (RR) of HZ in SARS-CoV-2-confirmed versus SARS-CoV-2-free individuals was estimated by a multivariable negative binomial regression adjusted by age, sex, and comorbidities. RESULTS: Data from 4,085,590 adults were analyzed. The overall HZ incidence rate in adults was 5.76 (95% confidence interval [CI], 5.66-5.85) cases per 1000 person-years. Individuals ≥18-year-old with SARS-CoV-2-confirmed infection had a 19% higher risk of developing HZ versus SARS-CoV-2-free ≥18-year-olds (adjusted RR = 1.19; 95% CI, 1.09-1.29); this percentage was 16% (adjusted RR = 1.16; 95% CI, 1.05-1.29) in ≥50-year-olds. Severe (hospitalized) cases of SARS-CoV-2 infection had a 64% (if ≥18 years old) or 44% (if ≥50 years old) higher risk of HZ versus nonhospitalized cases. CONCLUSION: These results support an association between SARS-CoV-2 infection and HZ, with a greater HZ risk in severe cases of SARS-CoV-2 infection.

A comparison of four self-controlled study designs in an analysis of COVID-19 vaccines and myocarditis using five European databases.

INTRODUCTION: The aim of this study was to assess the possible extent of bias due to violation of a core assumption (event-dependent exposures) when using self-controlled designs to analyse the association between COVID-19 vaccines and myocarditis. METHODS: We used data from five European databases (Spain: BIFAP, FISABIO VID, and SIDIAP; Italy: ARS-Tuscany; England: CPRD Aurum) converted to the ConcePTION Common Data Model. Individuals who experienced both myocarditis and were vaccinated against COVID-19 between 1 September 2020 and the end of data availability in each country were included. We compared a self-controlled risk interval study (SCRI) using a pre-vaccination control window, an SCRI using a post-vaccination control window, a standard SCCS and an extension of the SCCS designed to handle violations of the assumption of event-dependent exposures. RESULTS: We included 1,757 cases of myocarditis. For analyses of the first dose of the Pfizer vaccine, to which all databases contributed information, we found results consistent with a null effect in both of the SCRI and extended SCCS, but some indication of a harmful effect in a standard SCCS. For the second dose, we found evidence of a harmful association for all study designs, with relatively similar effect sizes (SCRI pre = 1.99, 1.40 - 2.82; SCRI post 2.13, 95 %CI - 1.43, 3.18; standard SCCS 1.79, 95 %CI 1.31 - 2.44, extended SCCS 1.52, 95 %CI = 1.08 - 2.15). Adjustment for calendar time did not change these conclusions. Findings using all designs were also consistent with a harmful effect following a second dose of the Moderna vaccine. CONCLUSIONS: In the context of the known association between COVID-19 vaccines and myocarditis, we have demonstrated that two forms of SCRI and two forms of SCCS led to largely comparable results, possibly because of limited violation of the assumption of event-dependent exposures.