Knowing the time you got vaccinated against COVID-19 is important: a study shows that it is better in the afternoon

An observational study has revealed that antibody levels are higher in people who receive the COVID-19 vaccine in the afternoon. Thus, this work, published in the journal ‘Journal of Biological Rhythms’, shows that the response to the vaccine can be affected by circadian rhythms. “Our observational study provides proof of concept that time of day affects the immune response to the SARS-CoV-2 vaccine, findings that may be relevant to optimize the efficacy of the vaccine“explains co-author Elizabeth Klerman, a researcher in the Division of Neurophysiology, Sleep Unit at Massachusetts General Hospital (MGH).

Our internal 24-hour circadian clock regulates many aspects of physiology, including response to infectious diseases and vaccination. The symptoms of some diseases and the action of many medications vary according to the time of day. People with lung diseases tend to have a greater severity of symptoms and an alteration in respiratory function at certain times of the day, for example. A study of older men who got the flu vaccine showed that they had higher antibody titers when they received the vaccine in the morning compared to the afternoon.

“Trials have shown that giving some chemotherapeutic agents at a specific time of day effectively targets cancer cells, but limits toxicity to other cells“says Klerman. This new observational study assessed post-vaccination antibody levels against SARS-CoV-2 among 2,190 UK healthcare workers. Blood samples were collected from asymptomatic hospital workers at the time of vaccination.

Antibody responses were also higher in those who received the Pfizer mRNA vaccine, in women, and in younger people.

Researchers created a model to investigate the effect on antibody levels based on time of day of vaccination, type of vaccine (Pfizer mRNA vaccine or AstraZeneca adenoviral vaccine), age, sex, and number days after vaccination. The researchers found that antibody responses were higher overall for everyone who got vaccinated later in the day. Antibody responses were also higher in those who received the Pfizer mRNA vaccine, in women and in younger people, in addition to the effect of the time of day of vaccination.

The SARS-CoV-2 study contrasts with earlier studies in older men who reported higher flu titers in the morning. These are the possible reasons for these disparate results. “The SARS-CoV-2 vaccine and the influenza vaccine have different mechanisms of action from each other, and the antibody response can vary greatly depending on whether the immune system recognizes the pathogen from previous infections, such as influenza. , or if you are facing a new virus, “says Klerman.

A limitation of the study was the lack of data on the medical and medication history of the participantsas well as your sleep and shift work patterns, which can also influence your response to the vaccine. “We must replicate our results and better understand the underlying physiology of SARS-CoV-2 and the body’s response to the vaccine before we can recommend that people who want an additional vaccine booster, such as the elderly or immunosuppressed, schedule your vaccine for the afternoon. This research is the first step to demonstrate the importance of the time of response to the vaccine against SARS-CoV-2 “, Klerman emphasizes.