Increased Transmissibility of the SARS-CoV-2 Alpha Variant in a Japanese Population

To assess the relative transmissibility of the SARS-CoV-2 Alpha variant compared to the pre-existing SARS-CoV-2 in Japan, we performed a cross-sectional study to determine the secondary attack rate of COVID-19 in household contacts before and after the Alpha variant became dominant in Osaka. We acce...

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Bibliographic Details
Published in:International journal of environmental research and public health 2021-07, Vol.18 (15), p.7752
Main Authors: Tanaka, Hideo, Hirayama, Atsushi, Nagai, Hitomi, Shirai, Chika, Takahashi, Yuki, Shinomiya, Hiroto, Taniguchi, Chie, Ogata, Tsuyoshi
Format: Article
Language:English
Subjects:
Contact tracing
Coronaviruses
COVID-19
COVID-19 vaccines
Cross-Sectional Studies
Epidemics
Error analysis
Fever
Households
Humans
Immunization
Infections
Infectious diseases
Japan - epidemiology
Mutation
Population
Regression analysis
SARS-CoV-2
Severe acute respiratory syndrome
Severe acute respiratory syndrome coronavirus 2
Viruses
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Summary:To assess the relative transmissibility of the SARS-CoV-2 Alpha variant compared to the pre-existing SARS-CoV-2 in Japan, we performed a cross-sectional study to determine the secondary attack rate of COVID-19 in household contacts before and after the Alpha variant became dominant in Osaka. We accessed 290 household contacts whose index cases were diagnosed between 1 and 20 December 2020 (the third epidemic group), at a time when Osaka was free of the Alpha variant. We also accessed 398 household contacts whose index cases were diagnosed between 20 April and 3 May 2021 (the fourth epidemic group), by which time the Alpha variant had become dominant. We identified 124 household contacts whose index case was determined positive for the Alpha variant (Alpha group) in this fourth group. The secondary attack rates in the fourth group (34.7%) and the Alpha group (38.7%) were significantly higher than that in the third group (19.3%, < 0.001). Multivariable Poisson regression analysis with a robust error variance showed a significant excess risk in the fourth group (1.90, 95% CI = 1.47-2.48) and the Alpha group (2.34, 95% CI = 1.71-3.21). This finding indicates that the SARS-CoV-2 Alpha variant has an approximately 1.9-2.3-fold higher transmissibility than the pre-existing virus in the Japanese population.
ISSN:1660-4601
1661-7827
1660-4601
DOI:10.3390/ijerph18157752