A new study published in the Journal of Biological Rhythms demonstrates that antibody levels may be higher when people receive the SARS-CoV-2 vaccine in the afternoon versus the morning, according to a news release from Massachusetts General Hospital.
“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 optimizing the vaccine’s efficacy,” said co-senior author Elizabeth Klerman, MD, PhD, Research Investigator, Division of Neurophysiology, Sleep Unit, at Massachusetts General Hospital (MGH).
The observational study evaluated antibody levels after SARS-CoV-2 vaccination among 2,190 healthcare workers in the United Kingdom. As part of the UK’s infection prevention program, 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 based on time of day of vaccination, vaccine type (Pfizer mRNA vaccine or AstraZeneca adenoviral vaccine), age, sex, and the number of days post-vaccination.
The researchers found that antibody responses were higher, in general, for everyone who was vaccinated later in the day. The 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 time of day of vaccination.
The SARS-CoV-2 study contrasts with earlier studies in elderly men that reported higher anti-influenza titers in the morning. Potential reasons for the disparate findings: “The SARS-CoV-2 vaccine and the influenza vaccine have different mechanisms of action from each other, and antibody response may vary greatly depending on whether the immune system recognizes the pathogen from earlier infections, such as influenza, or whether it is confronted by a novel virus,” says Klerman.
A limitation of the study was the lack of data on participants’ medical and medication history, their sleep and shift-work patterns, which can also influence vaccine responses.
“We need to replicate our findings and develop a better understanding of the underlying physiology of SARS-CoV-2 and the body’s response to vaccination(s) before we can recommend that people who want an extra boost from the vaccine, such as older individuals or those who are immunocompromised, schedule their vaccine for the afternoon,” says Klerman. “This research is the first step in demonstrating the importance of time-of-day response to SARS-CoV-2 vaccine.” Klerman emphasizes that getting vaccinated, regardless of the time of day, is the most critical step in preventing COVID-19 infection.