Want best protection from COVID vaccine? Time of day you get it may matter, study says

Steven Senne/AP
·4 min read

Each cell in your body can tell what time of day it is and adjust its behaviors accordingly, such as producing hormones at night that make you sleepy and telling your brain you’re hungry around noon.

Decades of research have demonstrated your immune system follows your body’s 24-hour internal clock, formally called your circadian rhythm, in ways that could affect how you respond to medications, exposure to viruses and vaccinations.

Now, new research suggests the time of day you receive your COVID-19 shot may influence how much protection your body builds.

A study of 2,784 health care workers from the U.K. found coronavirus antibody levels were higher in people vaccinated in the afternoon than in the morning, contrary to what past research on other shots, such as the flu vaccine, has shown.

Antibody responses were also higher among people who got the Pfizer COVID-19 vaccine, as opposed to the AstraZeneca shot which is not authorized in the U.S., and in women and younger people, according to the study published Dec. 4 in the Journal of Biological Rhythms.

The team measured antibody levels via blood samples collected two to 10 weeks after vaccination with a first COVID-19 vaccine dose. The study was limited by a lack of data on participants’ medical history and sleep and work patterns, which could affect vaccine responses, according to the paper. It also didn’t include children, older people or those who are immunocompromised.

Researchers from the Massachusetts General Hospital in Boston say increased antibody levels among afternoon vaccinees may indicate more intense side effects as a result, but they admit more study is needed to better understand how time influences responses to COVID-19 vaccines.

If a period of time is guaranteed to mount an elevated immune response, researchers say they and other experts could “recommend that people who want an extra boost from the vaccine, such as older individuals or those who are immunocompromised, schedule” their shot during a certain time of day, co-senior author of the study Dr. Elizabeth Klerman, research investigator of the division of neurophysiology sleep unit at Massachusetts General Hospital, said in a news release.

Until additional studies are conducted, Klerman says COVID-19 vaccination is “the most critical step in preventing” coronavirus infection, “regardless of the time of day.”

Our ‘body clock’ determines where our immune cells go throughout the day

A separate study published in 2016 found flu vaccines produced more antibodies in 276 adults over 65 when they got their shots in the morning compared to the afternoon, opposite of what the new coronavirus study found.

“The [coronavirus] 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,” Klerman noted in the release.

Other research on the Venezuelan equine encephalomyelitis virus vaccine found mornings produced more antibodies, while afternoons proved more productive for the hepatitis B vaccine.

Time of day could influence disease severity and reactions to medications, too.

Researchers say specific timing can limit “toxicity to other cells” during chemotherapy treatment and some people with lung disease can experience worse symptoms at certain times of the day.

“Our immune system is composed of many different types of immune cells that are continually patrolling the body looking for evidence of infection or damage. But it is our body clock that determines where those cells are located at particular times of the day,” Annie Curtis, a senior lecturer of medicine and health sciences at the Royal College of Surgeons in Ireland, wrote in a June post for The Conversation.

Daily fluctuations in hormones could play a role, as well, though these factors may differ depending on the type of vaccine in question.

Get vaccinated regardless of time of day, experts say

Interestingly, the receptor that allows the coronavirus to enter human cells is controlled by your body’s internal clock, Curtis said, which could explain why higher levels of it are found in your airways during certain times of the day.

“Whether the time of day we’re vaccinated against COVID-19 impacts immune response remains to be answered. Given the high effectiveness of many COVID-19 vaccines and the urgency with which we need to vaccinate, people should be vaccinated at whatever time of day is possible for them,” Curtis wrote.

“But current and future vaccines which do not have such high efficacy rates — such as the flu vaccine — or if they’re used in people with poorer immune response (such as older adults), using a more precise ‘timed’ approach may ensure better immune response,” she continued.

Our goal is to create a safe and engaging place for users to connect over interests and passions. In order to improve our community experience, we are temporarily suspending article commenting