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Updated: Sep 21, 2025
Author Spotlight: A Pseudotype Virus System for Assessing Omicron Subvariants and Neutralizing Antibodies in SARS-CoV-2 Research
Published on: September 8, 2023
Shorter Incubation Period among COVID-19 Cases with the BA.1 Omicron Variant
Hideo Tanaka1, Tsuyoshi Ogata2, Toshiyuki Shibata3
1Public Health Center of Neyagawa City, Neyagawa 572-0838, Japan.
Abstract:
We aimed to elucidate the range of the incubation period in patients infected with the SARS-CoV-2 Omicron variant in comparison with the Alpha variant. Contact tracing data from three Japanese public health centers (total residents, 1.06 million) collected following the guidelines of the Infectious Diseases Control Law were reviewed for 1589 PCR-confirmed COVID-19 cases diagnosed in January 2022. We identified 77 eligible symptomatic patients for whom the date and setting of transmission were known, in the absence of any other probable routes of transmission. The observed incubation period was 3.03 ± 1.35 days (mean ± SDM). In the log-normal distribution, 5th, 50th and 95th percentile values were 1.3 days (95% CI: 1.0−1.6), 2.8 days (2.5−3.1) and 5.8 days (4.8−7.5), significantly shorter than among the 51 patients with the Alpha variant diagnosed in April and May in 2021 (4.94 days ± 2.19, 2.1 days (1.5−2.7), 4.5 days (4.0−5.1) and 9.6 days (7.4−13.0), p < 0.001). As this incubation period, mainly of sublineage BA.1, is even shorter than that in the Delta variant, it is thought to partially explain the variant replacement occurring in late 2021 to early 2022 in many countries.
Insights
The Omicron variant of SARS-CoV-2 has a significantly shorter incubation period (3.03 days) compared to the Alpha variant (4.94 days). This rapid incubation may explain Omicron
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- The SARS-CoV-2 Omicron variant (B.1.1.529) rapidly replaced previous variants globally.
- Understanding the incubation period of Omicron is crucial for effective contact tracing and control measures.
Purpose of the Study:
- To compare the incubation period of the SARS-CoV-2 Omicron variant with the Alpha variant.
- To investigate the potential impact of incubation period on variant replacement dynamics.
Main Methods:
- Retrospective analysis of contact tracing data from 1.06 million residents across three Japanese public health centers.
- Identification of 77 symptomatic COVID-19 cases linked to known transmission events for Omicron (BA.1 sublineage) and 51 cases for Alpha.
- Calculation of incubation periods using mean, standard deviation, and log-normal distribution percentiles.
Main Results:
- The mean incubation period for Omicron was 3.03 ± 1.35 days, with 5th, 50th, and 95th percentiles of 1.3, 2.8, and 5.8 days, respectively.
- This is significantly shorter than the Alpha variant's mean incubation period of 4.94 ± 2.19 days (5th, 50th, 95th percentiles: 2.1, 4.5, and 9.6 days).
- The Omicron incubation period is also shorter than that observed for the Delta variant.
Conclusions:
- The SARS-CoV-2 Omicron variant exhibits a significantly shorter incubation period compared to the Alpha variant.
- This shortened incubation period likely contributed to the rapid global spread and replacement of previous SARS-CoV-2 variants by Omicron.
