Is there a best time of day to get vaccinated?
Does it matter whether you receive a vaccine in the morning or the afternoon? This was the question explored by our team member Dr Cathy Wyse in a recent episode of the Light O'Clockpodcast.
Light O'Clock is a science podcast that explores how light and biological timing shape human health, sleep, and daily life, and is produced at the Max Plank Institute for Biological Cybernetics, Tübingen, Germany.
Cathy joined the podcast to discuss her systematic review, Circadian Variation in the Response to Vaccination: A Systematic Review and Evidence Appraisal. The review examined research investigating whether the time of day at which a vaccine is administered can influence the immune response. This review was completed during Cathy's time as a Research Fellow at Maynooth University, together with colleagues from the Kathleen Lonsdale Institute: Laura Rudderham (former research assistant), Enya Nordon (PhD student), Professor Andrew Coogan and Professor Lorna M. Lopez, as well as collaborator Dr Louise M. Ince, University of Texas at Austin, Austin, Texas, USA.
As explained in the podcast, there is good reason to ask the question. The human immune system follows circadian rhythms, with immune-cell activity, movement, and metabolism changing across the day. This makes it biologically plausible that our response to vaccination could also vary depending on timing.
However, the findings from Cathy's review show that the evidence so far is inconsistent. Studies differ substantially in their design, the vaccines and populations investigated, and even how they define morning and evening. Some studies have reported stronger responses following morning vaccination, others following an afternoon or evening vaccination, while others have found no meaningful difference.
The takeaway message from Cathy's research is clear, there is currently not enough evidence to recommend a particular time of day for vaccination. More carefully designed studies, including randomised controlled trials and better consideration of individual circadian timing, will be needed to determine whether vaccination timing could eventually have clinical relevance.
In the podcast, Cathy discusses these findings alongside the fascinating relationship between our body clocks and immune system, the challenges of studying vaccination timings in humans, and what future research in this area might look like.
