Longer incubation period of coronavirus disease 2019 (COVID‐19) in older adults

OBJECTIVE: The aim of this study was to explore any age‐related change in the incubation period of COVID‐19, specifically any difference between older (aged ≥65 years) and younger adults. METHODS: Based on online data released officially by 21 Chinese cities from January 22 to February 15, 2020, the incubation period of COVID‐19 patients who had travelled to Hubei was studied according to age. Previous studies were reviewed and compared. RESULTS: The study recruited 136 COVID‐19 patients who had travelled to Hubei during January 5‐31, 2020, stayed for 1‐2 days, and returned with symptom onset during January 10‐February 6, 2020. The median age was 50.5 years (range 1‐86 years), and 22 patients (16.2%) were aged ≥65 years. The age‐stratified incubation period was U‐shaped with higher values at extremes of age. The median COVID‐19 incubation period was 8.3 (90% confidence interval [CI], 7.4‐9.2) days for all patients, 7.6 (90% CI, 6.7‐8.6) days for younger adults, and 11.2 (90% CI, 9.0‐13.5) days for older adults. The 5th/25th/75th/90th percentiles were 2.3/5.3/11.3/14.2 days for all, 2.0/5.0/10.5/13.2 days for younger adults, and 3.1/7.8/14.4/17.0 days for older adults. There were 11 published studies on COVID‐19 incubation periods up to March 30, 2020, reporting means of 1.8‐7.2 days, and medians of 4‐7.5 days, but there was no specific study on the effect of age on incubation period. One study showed that severe COVID‐19 cases, which included more elderly patients, had longer incubation periods. CONCLUSION: Based on 136 patients with a travel history to Hubei, the epicenter of COVID‐19, the COVID‐19 incubation period was found to be longer in older adults. This finding has important implications for diagnosis, prevention, and control of COVID‐19.