A valid measurement of the SARS-CoV-2 incubation period is needed for
case definitions and for adapting appropriate isolation measures but is
challenging in an emergency context. The objective was to systematically
review recent literature of reported estimates of the distribution of
incubation period of SARS-CoV-2 for describing the distribution and its
variability and dispersion through meta-analysis. A systematic review
search was carried out up to July 1st 2020 of all identified references
available reporting the SARS-CoV-2 incubation. Individual mean and
standard deviation were used to produce the pooled estimate.
Heterogeneity was also assessed using I2 statistics and sources of
heterogeneity were explored using a meta-regression. The main outcome
was the SARS-CoV-2 incubation period defined as the time from exposure
to onset of clinical illness. In total, 43 studies were eligible,
including 12 (27.9%) cohorts and 31 (72.1%) case reports and series.
The pooled estimate of the mean incubation period across the studies was
6.24 days, 95% CI [5.80;6.69] ranging from 2.33 to 17.60 days.
Shorter incubation periods were reported in cohorts compared to case
series (p<0.01) and among studies with high proportions of
males (p<0.05). The mean incubation period will help for
identification times of exposure but determinants of its
variations/range might be explored for potential links with clinical
outcome or early pathogenic steps. The impact of individuals with
extreme values of incubation on the outbreak dynamic should be evaluated
taking account for the basic reproductive number. A real time of
meta-analysis, called the InCoVid Lyon, is proposed.