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Increased Secondary Attack Rates among the Household Contacts of Patients with the Omicron Variant of the Coronavirus Disease 2019 in Japan

Author

Listed:
  • Tsuyoshi Ogata

    (Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan)

  • Hideo Tanaka

    (Public Health Center of Neyagawa City Government, Neyagawa 572-0838, 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)

  • Yukino Osaki

    (Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan)

  • Ayane Tono

    (Itako Public Health Center of Ibaraki Prefectural Government, Itako 311-2422, Japan)

  • Koji Wada

    (Department of Public Health, Faculty of Medicine, International University of Health and Welfare, Tokyo 107-8402, Japan)

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.

Suggested Citation

  • Tsuyoshi Ogata & Hideo Tanaka & Emiko Tanaka & Natsumi Osaki & Etsuko Noguchi & Yukino Osaki & Ayane Tono & Koji Wada, 2022. "Increased Secondary Attack Rates among the Household Contacts of Patients with the Omicron Variant of the Coronavirus Disease 2019 in Japan," IJERPH, MDPI, vol. 19(13), pages 1-11, June.
    • Handle: RePEc:gam:jijerp:v:19:y:2022:i:13:p:8068-:d:853054
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    References listed on IDEAS

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    1. Hideo Tanaka & Tsuyoshi Ogata & Toshiyuki Shibata & Hitomi Nagai & Yuki Takahashi & Masaru Kinoshita & Keisuke Matsubayashi & Sanae Hattori & Chie Taniguchi, 2022. "Shorter Incubation Period among COVID-19 Cases with the BA.1 Omicron Variant," IJERPH, MDPI, vol. 19(10), pages 1-7, May.
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