How Our Immune System Clocks Into Work

A recent study from the Washington School of Medicine has suggested that the COVID-19 mRNA vaccine may be better at preventing infection if doses are administered around midday^⁴. When responding to viral infections or cancer, a group of immune cells known as CD8+ T cells become activated and generate a robust immune response that attacks and destroys infected or cancerous cells. Several studies have shown that CD8+ T cells function quite differently depending on the time of day. While these cells were found to be highly active at noon, they generated much weaker antiviral responses in the mornings and evenings, entering an almost sleep-like state^³. “Chronovaccination” is an emerging concept in immunology which suggests that circadian rhythms can be harnessed to optimize vaccine responses based on the time of day. This is particularly important for higher-risk individuals whose immunocompromised state can prevent a robust vaccine response^⁵. (insert illustration of a CD8+ T cell in a sleep-like state vs active state)

So, what does the fact that vaccinations are more effective at midday mean for night owls or those who work night shifts? Research shows that we might not need to panic if our circadian clock doesn’t follow a typical pattern. A study published this year in The Lancet’s eClinicalMedicine investigates the idea that everyone has a personalized internal clock, or “chronotype”, which can be harnessed so that even those with irregular sleep schedules can benefit from circadian timing of treatment delivery^⁶. A chronotype refers to a person’s natural inclination towards certain sleep and wake times, determined by complex interactions between our genetically encoded “clock proteins”, and environmental factors like whether we are early birds or night owls^⁶. In the study, chronotypes were used to optimize the time of delivery of hypertension drugs for each patient’s sleep schedule, which reduced the risk of a heart attack. The importance of timing in drug delivery is not a new concept — doctors and scientists have known that the time of day matters for the delivery of several drugs, with an estimated 50% of prescription medications hitting targets in the body that have circadian patterns^⁷. However, recognizing that everyone operates on a unique schedule brings a new layer of personalization to medical treatment. So whether you are getting your annual flu shot, insulin injection, or life-saving chemotherapy, it’s important to know that timing can make a significant difference, and understanding your chronotype could help ensure that your immune system is ready when it matters most.