RESUMO
BACKGROUND: We evaluated the effectiveness of coronavirus disease 2019 vaccination in high-risk facilities in the Republic of Korea during the period when the highly transmissible Delta variant was prevalent. Additionally, we aimed to explore any disparities in vaccine effectiveness (VE) across various types of institutions, specifically distinguishing between non-medical and medical establishments. METHODS: We examined 8 outbreak clusters covering 243 cases and 895 contacts from 8 high-risk facilities divided into 2 groups: group A (4 non-medical institutions) and group B (4 medical institutions). These clusters were observed from July 27, 2021 to October 16, 2021 for the attack rate (AR) and VE with respect to disease severity. A generalized linear model with a binomial distribution was used to determine the odds ratio (OR) for disease severity and death. RESULTS: AR was notably lower in group B (medical institutions). Furthermore, VE analysis revealed that group A exhibited higher effectivity for disease severity and death than group B. The OR for disease severity was 0.24 (95% confidence interval [CI], 0.03-2.16) for group A and 0.27 (95% CI, 0.12-0.64) for group B, with the OR for death at 0.12 (95% CI, 0.01-1.32) in group A and 0.34 (95% CI, 0.14-0.87) in group B. CONCLUSION: Although VE may vary across institutions, our findings underscore the importance of implementing vaccinations in high-risk facilities. Customized vaccination programs, tailored response plans, and competent management personnel are essential for effectively addressing and mitigating public health challenges.
RESUMO
OBJECTIVES: Household contacts of confirmed cases of coronavirus disease 2019 (COVID-19) areexposed to a high risk of viral transmission, and secondary incidence is an important indicatorof community transmission. This study analyzed the secondary attack rate and mRNA vaccineeffectiveness against transmission (VET) for index cases (patients treated at home) confirmedto be infected with the Delta and Omicron variants. METHODS: The subjects of the study were 4,450 index cases and 10,382 household contacts.Logistic regression analysis was performed to compare the secondary attack rate byvaccination status, and adjusted relative risk and 95% confidence intervals were identified. RESULTS: The secondary attack rate of the Delta variant was 27.3%, while the secondary attackrate of the Omicron variant was 29.8%. For the Delta variant, groups with less than 90 daysand more than 90 days after 2 doses of mRNA vaccination both showed a VET of 37%. For theOmicron variant, a 64% VET was found among those with less than 90 days after 2 doses ofmRNA vaccination. CONCLUSION: This study provides useful data on the secondary attack rate and VET of mRNAvaccines for household contacts of COVID-19 cases in South Korea.
