Abstract
This study investigated the household secondary attack rate (HSAR) of patients with coronavirus disease (COVID-19) during the omicron variant-dominant period. The HSAR of COVID-19 cases during the omicron variant-dominant period (4-20 January 2022) was calculated and compared with the delta variant-dominant period (20 August to 7 November 2021) in Itako, Japan. In Itako, all 47 and 119 samples tested during the omicron and delta variant-dominant periods were negative and positive, respectively, for the L452R mutation. We used a generalized estimating equation regression model. The HSAR was 31.8% (95% confidence interval (CI) 27.7-36.2) for 456 household contacts during the omicron variant-dominant period; it was higher than that during the delta variant-dominant period (25.2%) (adjusted risk ratio [aRR] 1.61, CI 1.13-2.28). During the omicron variant-dominant period, HSAR was lower for the household contacts of completely vaccinated index patients (27.3%) than for contacts of other index patients (41.2%) (vaccine effectiveness for infectee 0.43, 95% CI 0.16-0.62) and was significantly higher for female contacts than for male contacts (36.2% vs. 26.1%; aRR 1.29, 95% CI 1.01-1.65). The HSAR was significantly higher during the omicron variant-dominant period than the delta variant-dominant period. The vaccination of index patients might protect household contacts.
Keywords: COVID-19; Delta variant; Japan; Omicron variant; SARS-CoV-2; household transmission; secondary attack rate; sex; vaccine effectiveness.
【저자키워드】 COVID-19, SARS-CoV-2, Sex, delta variant, secondary attack rate, Japan, household transmission, Omicron variant, vaccine effectiveness., 【초록키워드】 coronavirus disease, Vaccine, vaccination, Mutation, Delta, risk, omicron, delta variant, secondary attack rate, L452R, attack rate, Regression model, male, female, Patient, Effectiveness, Japan, household transmission, Omicron variant, household contact, household contacts, risk ratio, Contact, 95% CI, 95% confidence interval, COVID-19 case, Itako, PROTECT, tested, investigated, calculated, adjusted, significantly higher, aRR, negative and positive, 【제목키워드】 household, attack, secondary, Rate, Increased,