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Longer incubation periods of SARS-CoV-2 infection in infants

Objective: A large body of research has described the incubation period of SARS-CoV-2 infection, an important metric for assessing the risk of developing a disease as well as surveillance. While longer incubation periods for elderly have been found, it remains elusive whether this also holds true for infants and children, partly due to the lack of data. The present work clarified the incubation periods of COVID-19 for infants and children. Methods: Using the data released by the Chinese health authorities and municipal offices, statistical comparisons of clinical features were made between infants (aged below 1 year) and children (aged between 1 and 17 years). An age-varying incubation period distribution period was modeled using maximum likelihood estimation modified for interval censored exposure time and age. Discussion: Reported in 56 web pages, a total of 65 cases from 20 provinces dated between January and June 2020, including 18 infants and 47 children, were eligible for inclusion. Infants appeared to bear more severe clinical courses, as demonstrated by the higher prevalence of breathing difficulty as well as nasal congestion. In contrast, fever was less prominent in infants than in children. The incubation period was found to decrease with age, with infants appearing to have longer incubation periods. Conclusion: Fever remained to be one of the most commonly seen symptoms in infants and children with SARS-CoV-2 infection and have continued to determine the time of symptom onset. While shorter incubation periods should be seen in patients with weaker immune system due to weaker antiviral response that is beneficial for viral growth, the longer incubation period in infants may be due to their weaker febrile response to the virus, leading to prolonged symptom onset.