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This longitudinal observational study investigated the risk of breakthrough SARS-CoV-2 infection up to 6 months after a booster dose of an mRNA COVID-19 vaccine in infection-naïve vs. previously infected healthcare workers (HCWs), and whether this difference varied over time. A Cox proportional hazard regression model with Aalen’s additive analysis was fitted to examine the association between the risk of infections and predictor variables. Overall, we observed an incidence rate of 2.5 cases per 1000 person-days (95% confidence interval [CI] 2.0–3.0), which dropped at 0.8 per 1000 person-days (95% CI 0.3–2.0) in recipients with prior SARS-CoV-2 infection. The fitted analysis indicated an adjusted hazard ratio of 0.32 (95% CI 0.13–0.80; p-value = 0.01) for those with hybrid immunity with a slope that became steeply negative roughly starting from day 90. No difference was seen according to participants’ smoking habits. Characteristics of infected HCWs were also described. Our study quantifies the time-varying effects of vaccine-induced and hybrid immunity after the booster dose (during the Omicron variant predominance in Italy) and observed that the protection waned more rapidly in infection-naïve recipients starting from the third month. The results add important evidence that can be used to inform COVID-19 vaccination strategies.

WHAT IS KNOWN AND OBJECTIVE: Medication errors, such as unnecessary treatment discontinuation during treatment with direct-acting antivirals (DAAs), can lead to imbalances in the benefit-to-risk ratio. This risk is especially high when the medication error leads to adverse drug reactions (ADRs). However, to date, evidence on the frequency of this phenomenon is scarce. This study aims to provide better insight into ADRs possibly due to medication errors leading to DAA discontinuation and their preventability.METHODS: The Italian Pharmacovigilance Network database was used to extract individual case safety reports (ICSRs) generated from July 2012 to March 2017 via the Campania Region (Italy) spontaneous reporting system. ICSRs that included ledipasvir/sofosbuvir, ombitasvir/paritaprevir/ritonavir, dasabuvir, daclatasvir, sofosbuvir, simeprevir or elbasvir/grazoprevir as suspected drugs were included in this study. A preventability assessment was then performed utilizing the "P-Method," an algorithm that evaluates known risk factors due to medication errors that can be detected in ICSRs.RESULTS AND DISCUSSION: Of the 355 cases included in this study, 6 (1.69%) were classified as preventable and 52 (14.6%) were classified as potentially preventable. The most frequently identified critical criteria (risk factor) for preventable or potentially preventable cases were drug-drug interactions and incorrect drug dosing as part of the antiviral treatment scheme. In total, 89 of the 355 cases (25.1%) discontinued use of the DAAs due to ADRs, of which 20 of the 89 cases (22.5%) were due to an unimportant medical event as classified by the European Medicine Agency important medical event list.WHAT IS NEW AND CONCLUSION: This study found a proportion of preventable/potentially preventable ADRs involving DAA, which could be improved in the Campania Region (Italy). Additionally, the study identified a high proportion of seemingly unnecessary DAA discontinuatio