This week Fred and Nick discuss the anecdotal reports on infection rate differences between shifts taking place at different times. There has been some data that demonstrates a higher incidence in two otherwise identical cohorts of individuals undergoing training. The daytime group operating during daylight hours has a much lower rate of COVID-19 infection based on the testing that takes place daily than the group that trains during the nighttime hours.

We discuss potential causes including:

• The impact of sleep on the immune system
• Possible selection bias based on those in the night shift
• Different activities and exposure outside the training time

The data is intriguing and warrants a more detailed look to see if there are any patterns to discern that night suggest causative effects.