Consolidating Estimates of the Incubation Period for Omicron Subvariants From the Literature and Their Comparison to the Estimate From Taiwan: A Systematic Review and Meta‐Analysis, September 2024

BACKGROUND: The COVID-19 pandemic was characterized by waves driven by distinct viral variants, including the Omicron variant, which emerged in October 2021. To formulate effective public health strategies and understand disease spread, accurate estimates of the incubation periods of these variants are important. Existing estimates often conflict due to biases caused by epidemic dynamics and selective inclusion of cases. Using data from Taiwan, where disease incidence remained low and contact tracing was comprehensive during the first months of the Omicron outbreak, this study aims to accurately estimate the incubation period of the Omicron (BA.1) variant incubation period. METHODS: We reviewed the first 100 Omicron BA.1 symptomatic cases reported in Taiwan's contact-tracing records (between December 2021 and January 2022). Of these, 69 had usable information. Data on exposure and symptom onset dates were fitted with the generalized gamma. A systematic search and meta-analysis on incubation periods for Omicron BA.1/2/4/5 subvariants was then conducted to derive pooled mean estimates for the incubation periods of each subvariant. RESULTS: The mean incubation period was estimated at 3.5 days (95% credible interval: 3.0-4.0 days), with no clear differences based on vaccination status or age. This estimate aligned closely with the pooled mean of 3.7 days (3.3-4.0 days) for Omicron BA.1 and of 3.7 days (2.3-5.1 days) for all considered Omicron variants BA.1/2 and BA.5. CONCLUSIONS: Omicron subvariants have a relatively shorter incubation period compared to previous SARS-CoV-2 variants. A continuous update of incubation period estimates, based on available data, is necessary to develop guidelines that can reduce the socioeconomic costs associated with COVID-19.