top of page

From contact to symptoms – how long was the clock ticking for Omicron

Updated: Aug 28, 2023

Launched in October 2020, the ComCor study investigates the environment, practices and places visited by people recently infected with SARS-CoV-2. The aim is to identify factors that might influence the COVID-19 incubation period, in other words the time between an infectious contact with the virus and the onset of the first symptoms.

Estimating the number of days from contact with an infected individual to the onset of symptoms, the incubation period, is crucial for designing strategies to combat infectious disease. Based on it, epidemiologists establish the duration of the quarantine, the testing, and the tracing of exposed individuals. Initially, the time from encountering someone infected by SARS-CoV-2 to when you started to feel the consequences was estimated to range between 5.1 and 6.5 days. But this range was changing as new variants emerged throughout the COVID-19 pandemic.

A study conducted on a subset of participants from the French population (ComCor case-control study) infected by SARS-CoV-2 between October 2020 and February 2022 analysed the SARS-CoV-2 incubation period and factors that influenced it. The SARS-CoV-2 variant that first appeared in France (historical variant) was used as the reference, with symptoms arising after 4.6 days. However, omicron caused a one-day earlier onset of symptoms than all other previously predominant variants (3.6 days). Shorter incubation periods were also observed in younger men, non-smokers, and upon contact with a highly contagious person (high viral inoculum) who was either “unmasked” or displayed symptoms. The elderly population, over 70 years old, had a more extended incubation period, experiencing symptoms about half (0.4) a day later.

The evidence of a shorter incubation period is essential to start tracing contacts and isolate as soon as possible. In addition, infectious disease modelling can use this evidence to estimate the effects of COVID-19 on health-care systems.

How long was your incubation period?


Galmiche S, Cortier T, Charmet T, Schaeffer L, Chény O, von Platen C, Lévy A, Martin S, Omar F, David C, Mailles A, Carrat F, Cauchemez S, Fontanet A. SARS-CoV-2 incubation period across variants of concern, individual factors, and circumstances of infection in France: a case series analysis from the ComCor study. Lancet Microbe. 2023 Jun;4(6):e409-e417. doi: 10.1016/S2666-5247(23)00005-8. PMID: 37084751

bottom of page