COVID-19 Incubation Periods Differ Depending on Variant

Incubation periods are one of the most significant epidemiological parameters when studying infectious diseases. Understanding incubation periods can impact the recommended public health strategies to minimize infection. Previously, little research was done to understand the differences in incubation periods between COVID-19 variants. A study in JAMA Network Open determined that COVID-19 incubation periods differ based on the variant. The Alpha variant had the most prolonged incubation period, and the Omicron variant had the shortest.

The incubation period is the time between exposure and the first onset of symptoms.

“Knowledge of the disease’s incubation period is of great significance for case definition, management of emerging threats, estimation of the duration of follow-up for contact tracing and secondary case detection, and the establishment of public health programs aimed at reducing local transmission,” stated the researchers in the publication.

Researchers in this publication conducted a systematic review and meta-analysis using data from 142 studies. The average incubation period for the 8112 patients included in this study was 6.57 days; however, the range was between 1.80 and 18.87 days.

After looking at the overall incubation period, the researchers looked at the incubation times for the Alpha, Beta, Delta, and Omicron variants separately.

The average incubation period for cases caused by the Alpha variant was 5.00 days, approximately 1.58 days longer than the 3.42 day incubation period for the Omicron variant.

The Beta and Delta variants had similar incubation periods at 4.50 and 4.41 days, respectively.

On top of observing variations in incubation times for different variants, researchers were also able to analyze differences among age groups. For patients over 60 years old, the average incubation time was 7.43 days, less than the 8.82 days for children under 18.

Despite the plethora of data presented, this trial did have some limitations. First, the sample size for each variant differed due to limited access to information. While 6,374 patients were used to determine the incubation period for the Alpha variant, only 10 patients were observed for the Beta variant.

“The estimate of the incubation period was computed with data with considerable heterogeneity. Possible sources of heterogeneity included difference in study population, data collection period, and method of analysis,” noted the investigators in the study.

While the data collected in this study does have some limitations, it can be used to guide additional studies on incubation periods which in turn will inform public health strategies. A focus on incubation period research may assist in developing improved methods for combating infectious disease spread.