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The Shrinking Incubation Period of COVID-19

The incubation period of the original, wild-type COVID-19 strain was 6.65 days, while the Omicron variant's incubation period has shortened to 3.42 days.

How long after a potential COVID-19 exposure will you become infected? Though many studies have estimated the incubation period of COVID-19, it is not well known whether the virus’s average incubation period has changed throughout the course of the pandemic.

A recent study, published this week in JAMA, conducted a systematic review of the incubation periods of different COVID-19 variants of concern. The investigators also sought to determine the overall pooled incubation period of COVID-19 and the average COVID-19 incubation period across different vulnerable populations.

Knowledge of COVID-19’s incubation period is vital, as it informs virus definition, contact tracing, patient follow-up, and public health protocol.

The meta-analysis utilized PubMed, EMBASE, and ScienceDirect to find peer-reviewed studies using the keywords novel coronavirusSARS-CoV-22019-nCoV, or COVID-19 and either incubation period or incubation. A total of 142 studies, with 8112 patients, met the inclusion criteria. From this review, the investigators determined the average incubation period to be 6.57 days, ranging from 1.80 to 18.87 days.

The incubation period of the wild-type, Wuhan strain was determined to be 6.65 days. Broken down by variants of concern, the incubation period of COVID-19 was 5.00 days for Alpha, 4.50 days for Beta, 4.41 days for Delta, and 3.42 days for Omicron. This suggests that as COVID-19 mutates, the incubation time decreases.

Analyzed by other demographics, the mean incubation period was 8.82 days for children, 7.43 days for patients over 60 years of age, 6.99 days for patients with non-severe illness, and 6.69 days for patients with severe illness.

COVID-19 seemed to have a longer incubation period than other acute respiratory viral infections, including human coronavirus (3.2 days), influenza A (1.43-1.64 days), parainfluenza (2.6 days), respiratory syncytial virus (4.4 days), and rhinovirus (1.4 days). Previous SARS studies have found the incubation period of to be correlated with disease severity, and fatal cases had the shortest incubation period.

These study findings indicate COVID-19 has and will likely continue to mutate, producing variants with enhanced transmission and virulence. Identifying the incubation period is vital to inform the length of isolation after an exposure. This highlights the importance of taking COVID-19 precautions to prevent its spread and inhibit infectious mutations.