Comparative Effectiveness of COVID-19 Bivalent Versus Monovalent mRNA Vaccines in the Early Stage of Bivalent Vaccination in Korea: October 2022 to January 2023.

BACKGROUND: This retrospective observational matched-cohort study of 2,151,216 individuals from the Korean coronavirus disease 2019 (COVID-19) vaccine effectiveness cohort aimed to evaluate the comparative effectiveness of the COVID-19 bivalent versus monovalent vaccines in providing additional protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, critical infection, and death in Korea. METHODS: Among individuals, those vaccinated with COVID-19 bivalent vaccines were matched in a 1:1 ratio with those who were vaccinated with monovalent vaccines (bivalent vaccines non-recipients) during the observation period. We fitted a time-dependent Cox proportional-hazards model to estimate hazard ratios (HRs) of COVID-19 outcomes for infection, critical infection, and death, and we defined vaccine effectiveness (VE) as 1-HR. RESULTS: Compared with the bivalent vaccination group, the incidence proportions in the monovalent vaccination group were approximately three times higher for infection, nine times higher for critical infection, and 11 times higher for death. In the early stage of bivalent vaccination, relative VE of bivalent vaccine against monovalent vaccine was 42.4% against SARS-CoV-2 infection, 81.3% against critical infection, and 85.3% against death. In addition, VE against critical infection and death according to the elapsed period after bivalent vaccination was maintained at > 70%. CONCLUSION: The bivalent booster dose provided additional protection against SARS-CoV-2 infections, critical infections, and deaths during the omicron variant phase of the COVID-19 pandemic.

Comparing the effectiveness of bivalent and monovalent COVID-19 vaccines against COVID-19 infection during the winter season of 2022-2023: A real-world retrospective observational matched cohort study in the Republic of Korea.

OBJECTIVES: To compare the effectiveness of bivalent and monovalent COVID-19 vaccines throughout the 2022-2023 winter season based on real-world data. METHODS: This retrospective observational matched cohort study used the national vaccination program and a surveillance dataset from the Republic of Korea, and included adults aged >18 years who received bivalent or monovalent COVID-19 vaccines between October 11, 2022, and December 17, 2022. Cox proportional hazard models were used to estimate the hazard ratio for COVID-19 infection between the groups. RESULTS: We included 29,245 matched individuals in the bivalent and monovalent vaccine groups, respectively. The bivalent vaccine recipients showed 12.2% (95% confidence interval [CI] 6.5-17.7%) additional protection against COVID-19 infection compared with the monovalent vaccine recipients. The additional protection provided by bivalent vaccines was significantly higher among residents of long-term care facilities (39.4%, 95% CI 21.6-53.1%). Maximum additional protection was observed 3 to 4 months after completing the vaccination (17.6%, 95% CI 6.6-27.3%). CONCLUSION: Bivalent COVID-19 vaccines showed significantly better protection against infection than monovalent vaccines among adults during the 2022-2023 winter season. Our results highlight that immunization programs with bivalent vaccines comprising recent variants can be an effective measure to prepare for seasonal COVID-19 circulation.

Stress, COVID-19 related knowledge, attitude, and infection control performance of nurses at long-term care hospitals.

This study aimed to identify the stress level, knowledge, attitude, and infection control performance of nurses at long-term care hospitals (LTCHs) designated for infectious disease management and to investigate factors contributing to infection control performance. A total of 178 nurses who had worked for at least 1 month at seven LTCHs designated for infectious disease management and provided care for patients confirmed with COVID-19 were enrolled in the study. Data were collected from February to March 2022 using written and online self-report questionnaires. COVID-19 infection control performance was higher among married than among single participants (t = -3.71, p < 0.001), among those aged 40-49 versus 30-39 years (F = 4.10, p = 0.003), and those with 1-2, 3-4, or ≥5 sessions versus no prior education (F = 6.41, p < 0.001). COVID-19 infection control performance was negatively correlated with stress (r = 0.26, p < 0.001) and positively correlated with knowledge (r = 0.40, p < 0.001) and attitude toward COVID-19 (r = -0.36, p < 0.001). Stress (ß = -0.17, p = 0.012), knowledge of COVID-19 (ß = 0.28, p < 0.001), attitude toward COVID-19 (ß = 0.20, p = 0.004), and marital status (ß = 0.18, p = 0.009) were identified as predictors of COVID-19 infection control performance.