Covid vaccine shot - Morning, afternoon? A recent study show “time of day affects immune response to Covid vaccination" and further suggest, “antibody levels are higher people take their shots later in the day." The research, published in the Journal of Biological Rhythms, demonstrates that our internal 24-hour circadian clock regulates many aspects of physiology, including the response to infectious disease and vaccination. "Our observational study provides proof of concept that time of day affects immune response to SARS-CoV-2 vaccination, findings that may be relevant for optimising the vaccine’s efficacy," said study co-senior author Elizabeth Klerman from Massachusetts General Hospital (MGH), US. Circadian signalling and how it works