Eurosurveillance - Volume 29, Issue 37, 12 September 2024

Long-term effectiveness data on bivalent COVID-19 boosters are limited.

We evaluated the long-term protection of bivalent boosters against severe COVID-19 among ≥ 65-year-olds in Finland.

In this register-based cohort analysis, we compared the risk of three severe COVID-19 outcomes among ≥ 65-year-olds who received a bivalent booster (Original/Omicron BA.1 or Original/BA.4–5; exposed group) between 1/9/2022 and 31/8/2023 to those who did not (unexposed). We included individuals vaccinated with at least two monovalent COVID-19 vaccine doses before 1/9/2022 and ≥ 3 months ago. The analysis was divided into two periods: 1/9/2022–28/2/2023 (BA.5 and BQ.1.X predominating) and 1/3/2023–31/8/2023 (XBB predominating). The hazards for the outcomes between exposed and unexposed individuals were compared with Cox regression.

We included 1,191,871 individuals. From 1/9/2022 to 28/2/2023, bivalent boosters were associated with a reduced risk of hospitalisation due to COVID-19 (hazard ratio (HR): 0.45; 95% confidence interval (CI): 0.37–0.55), death due to COVID-19 (HR: 0.49; 95% CI: 0.38–0.62), and death in which COVID-19 was a contributing factor (HR: 0.40; 95% CI: 0.31–0.51) during 14–60 days since vaccination. From 1/3/2023 to 31/8/2023, bivalent boosters were associated with lower risks of all three severe COVID-19 outcomes during 61–120 days since a bivalent booster (e.g. HR: 0.53; 95% CI: 0.39–0.71 for hospitalisation due to COVID-19); thereafter no notable risk reduction was observed. No difference was found between Original/Omicron BA.1 and Original/BA.4–5 boosters.

Bivalent boosters initially reduced the risk of severe COVID-19 outcomes by ca 50% among ≥ 65-year-olds, but protection waned over time. These findings help guide vaccine development and vaccination programmes.

In Europe and other high-income countries, antibiotics are mainly prescribed in the outpatient setting, which consists of primary, specialist and hospital-affiliated outpatient care. Established surveillance platforms report antimicrobial consumption (AMC) on aggregated levels and the contribution of the different prescriber groups is unknown.

To determine the contribution of different prescribers to the overall outpatient AMC in Switzerland.

We conducted a retrospective observational study using claims data from one large Swiss health insurance company, covering the period from 2015 to 2022. We analysed antibiotic prescriptions (ATC code J01) prescribed in the Swiss outpatient setting. Results were reported as defined daily doses per 1,000 inhabitants per day (DID) and weighted according to the total population of Switzerland based on census data.

We analysed 3,663,590 antibiotic prescriptions from 49 prescriber groups. Overall, AMC ranged from 9.12 DID (2015) to 7.99 DID (2022). General internal medicine (40.1% of all prescribed DID in 2022), hospital-affiliated outpatient care (20.6%), group practices (17.3%), paediatrics (5.4%) and gynaecology (3.7%) were the largest prescriber groups. Primary care accounted for two-thirds of the prescribed DID. Quantity and type of antibiotics prescribed varied between the prescriber groups. Broad-spectrum penicillins, tetracyclines and macrolides were the most prescribed antibiotic classes.

Primary care contributed considerably less to AMC than anticipated, and hospital-affiliated outpatient care emerged as an important prescriber. Surveillance at the prescriber level enables the identification of prescribing patterns within all prescriber groups, offering unprecedented visibility and allowing a more targeted antibiotic stewardship according to prescriber groups.