Study: Why it’s better to get vaccinated in the afternoon

An observational study has revealed that antibody levels are higher in people who receive the Covid-19 vaccine in the afternoon or evening.

The study, published in the Journal of Biological Rhythms, shows that the response to the vaccine may be affected by circadian rhythms.

“Our observational study provides proof that time of day affects the immune response to the SARS-CoV-2 vaccine, findings that may be relevant to optimising vaccine efficacy,” 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, for example, people with lung disease often have more severe symptoms and impaired respiratory function at certain times during the day.

A study of elderly men who were vaccinated against influenza showed that they had higher antibody titres when they received the vaccine in the morning compared to the afternoon.

Klerman says: “Trials have shown that administration of some chemotherapeutic agents at a specific time of day effectively targets cancer cells, but limits toxicity to other cells.”

This new observational study assessed antibody levels following SARS-CoV-2 vaccination among 2,190 healthcare workers in the UK. Blood samples were collected from asymptomatic hospital workers at the time of vaccination.

The researchers created a model to investigate the effect on antibody levels at certain times of the day, vaccine types (Pfizer mRNA vaccine or AstraZeneca adenoviral vaccine), age, sex and number of days post-vaccination.

The researchers found that antibody responses were higher overall for all those vaccinated later in the day. Antibody responses were also higher in those who received Pfizer’s mRNA vaccine, in women and in younger people.

A limitation of the study was the lack of data on the participants’ medical and medication history, as well as their sleep and shift work patterns, which may also influence the response to the vaccine.

“We need to 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 immunocompromised, schedule their vaccination for the evening.”

“This research is the first step in demonstrating the importance of the timing of the response to the SARS-CoV-2 vaccine,” Klerman adds.

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