Volume 28, Number 8—August 2022
Research
Transmissibility of SARS-CoV-2 B.1.1.214 and Alpha Variants during 4 COVID-19 Waves, Kyoto, Japan, January 2020–June 2021
Yasufumi Matsumura
, Miki Nagao, Masaki Yamamoto, Yasuhiro Tsuchido, Taro Noguchi, Koh Shinohara, Satomi Yukawa, Hiromi Inoue, and Takeshi Ikeda
, Miki Nagao, Masaki Yamamoto, Yasuhiro Tsuchido, Taro Noguchi, Koh Shinohara, Satomi Yukawa, Hiromi Inoue, and Takeshi Ikeda
Table 2
COVID-19 cases associated with households or clusters during the third and fourth disease waves, Kyoto, Japan*
| Variables | Third wave | Fourth wave |
|---|---|---|
| Date | 2020 Dec–2021 Feb | 2021 Apr–May |
| Total no. cases (mean no./d) | 4,592 (51.0) | 4,181 (68.5) |
| Total no. (%) secondary cases among households | 1,228 (26.7) | 1,208 (28.9) |
| Total no. (%) cases associated with clusters | 849 (18.5) | 449 (10.7) |
| Median no. cases associated with each cluster (IQR) | 11 (9–20.5) | 7 (6–9) |
| Total no. clusters (mean no./day) | 50 (0.56) | 43 (0.70) |
| Median test positivity of each cluster, % (IQR)† | 18 (9.7–37) | 34 (15.6–66.3) |
*IQR, interquartile range. †Calculated by using epidemiologic data available for 48 clusters in the third wave and 35 clusters in the fourth wave.
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