COVID-19 Incubation Period Varies by SARS-CoV-2 Strain

With the evolution of different COVID-19 variants, finding the mean incubation period has become more complex.

Consistent evolution and mutation of the SARS-CoV-2 virus throughout the pandemic has highlighted the importance of identifying the incubation period of variants, according to research results published in JAMA Network Open.

Researchers have conducted several studies to find the average incubation period of COVID-19; however, the evolution of different SARS-CoV-2 variants has made it increasingly difficult.

Investigators conducted a meta-analysis of 142 studies including 8112 patients with COVID-19. Of the 142 studies, 45 were strong, 82 were moderate, and 15 were weak. Most studies were conducted in China between January and March 2020.

Across these studies, the pooled incubation period was 6.57 days, with results ranging from 1.80 to 18.87 days. The incubation period for the Alpha variant of COVID-19 was 5 days while the Beta variant was 4.5 days, the Delta variant was 4.41 days, and the Omicron variant was 3.42 days. Taken together, these findings suggest a mean COVID-19 incubation period of 6.57 days—longer than those of other acute respiratory viral infections like the human coronavirus, influenza A, parainfluenza, respiratory syncytial virus, and rhinovirus.

This study contains several limitations. First, to determine incubation periods, knowledge of exposure to the virus and onset of symptoms were necessary. As most of this data was collected retrospectively, recall bias is possible.

Second, the data collected was diverse in study population, data collection periods, and methods of analysis. This resulted in the assumption that incubation periods were consistent across different populations. And third, there were not many studies on incubation periods caused by SARS-CoV-2 variants. Urgent timelines resulted in estimations of incubation periods in limited case numbers.

“Although variants such as Alpha, Beta, and Gamma are currently only prevalent in a few countries in Southeast Asia, South America, and Africa, the Delta and Omicron variants have become the dominant strains in many countries around the world,” the researchers wrote.“Identifying the incubation period of different variants is a key factor in determining the isolation period. The pooled incubation period of different variants is a key factor in determining the isolation period. The pooled incubation period of COVID-19 in this study was 6.57 days.”


  1. Wu Y, Kang L, Guo Z, Liu J, Liu M, Liang W. Incubation period of COVID-19 caused by unique SARS-CoV-2 strains: A systematic review and meta-analysis. JAMA Network Open. 2022;5(8):e2228008. doi:10.1001/jamanetworkopen.2022.28008