Increased Secondary Attack Rate among Unvaccinated Household Contacts of Coronavirus Disease 2019 Patients with Delta Variant in Japan

Tsuyoshi Ogata, Hideo Tanaka, Yumiko Nozawa, Kazue Mukouyama, Emiko Tanaka, Natsumi Osaki, Etsuko Noguchi, Kayoko Seo and Koji Wada
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Tsuyoshi Ogata: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Hideo Tanaka: Fujiidera Public Health Center of Osaka Prefectural Government, Fujiidera 583-0024, Japan
Yumiko Nozawa: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Kazue Mukouyama: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Emiko Tanaka: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Natsumi Osaki: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Etsuko Noguchi: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Kayoko Seo: Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan
Koji Wada: Department of Public Health, Faculty of Medicine and Graduate School of Public Health, International University of Health and Welfare, Tokyo 107-8402, Japan

IJERPH, 2022, vol. 19, issue 7, 1-11

Abstract: This study aimed to elucidate the household secondary attack rate (HSAR) of the Delta variant in comparison to the Alpha variant, and evaluate the risk factors among unvaccinated household contacts of patients with coronavirus disease 2019 (COVID-19). We studied household contacts of index cases of COVID-19 infected with Delta (L452R mutation), Alpha (N501Y mutation), and wild strain from December 2020 through November 2021 in Itako, Japan. The HSARs of the entire household contact, and the contact of index case with Delta variant were calculated and compared across the risk factors. We used a generalized estimating equation regression model for the multivariate analysis. We enrolled 1257 unvaccinated contacts from 580 households. The HSAR was higher in household contacts of index patients with Delta (48.5%) than with Alpha variant (21.7%) (aOR = 3.34, p = 0.000). In Delta variants, the HSAR was higher in household contacts with spousal relationships to index patients (63.4%) than contacts with other relationships (45.5%) (aOR 1.94, p = 0.026), and was lower in household contacts of index patients aged ≤19 (33.1%) than for contacts of index cases aged 20–59 years (52.6%) (aOR = 0.50, p = 0.027). The result of our study can be used to devise informed strategy to prevent transmission within households.

Keywords: COVID-19; SARS-CoV-2; Delta variant; Alpha variant; household transmission; secondary attack rate; unvaccinated; spouse; index patient; Japan (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2022
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