Analysis of data of over 1000 people who tested positive for COVID-19 in Wuhan, China has led researchers to conclude the incubation period of the virus could extend beyond a week.
Incubation period refers to the duration between onset of infection and emergence of symptoms. Incubation period of a disease can vary from person to person, however it is important to determine the average duration in order to control the disease spread. Incubation period helps authorities determine the duration of quarantine and to understand the nature of disease transmission and identify the cause of the outbreak. Currently, the estimated incubation period for COVID-19 is around 4 to 5 days, however, there is considerable ambiguity about this owing to the novelty of the virus and the limited research on the subject. The NIH (National Institutes of Health) have initiated a study which allows experts to frame a longer approximation regarding the incubation of COVID-19.
The researchers analysed data of 1,084 individuals from Wuhan, China who had tested positive for COVID-19, and found that the incubation period was around 7.6 days. The team reached this conclusion after following pre-symptomatic people from when they left Wuhan till the symptoms fully developed. The data was collected from public domains such as health commissions in China and health ministries from other countries. The team considered factors such as age, gender, date of first symptoms, date of onset, date of diagnosis, travel history, and date of leaving Wuhan. Incubation period was estimated using a mathematical model (renewal theory) which studies probability of processes over the course of time. The method diminishes recall bias regarding mistakes made while recalling past events such as travelling information.
Results showed that median incubation period was 7.76 days and mean incubation period was 8.3 days on average. In some cases, incubation period was found to be longer. For instance, it was 2 weeks for 10% of the people and around 20 days for 1%. Moreover, the youngest person in the study was 6-months old, and the eldest was 86 years old. Although, no evidence pointed out age as a determiner for a longer incubation period.