Not getting enough sleep shortly before or after getting a vaccine could reduce its effectiveness, especially in men, according to a study published Monday in Current Biology.

Study details and key findings

For the study, researchers looked at seven previous studies on 299 adults between the ages of 18 and 60 evaluating the relationship between sleep and immune function following vaccinations for influenza A and Hepatitis A and B.

The researchers analyzed both self-reported studies, where participants submitted their own sleep patterns, and objective studies, where participants' sleep patterns were tracked either by devices or in a sleep lab.

The self-reported studies found a reduction in antibodies among those who slept less than six hours, but the results were not "statistically significant." However, the objective studies saw a "robust decrease in antibody response" among men.

The researchers suggested the lack of statistically significant results in the self-reported studies may be due to participants overestimating how many hours they slept.

"Good sleep not only amplifies but may also extend the duration of protection of the vaccine," said senior author Eve Van Cauter, professor emeritus at the University of Chicago.

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Marc Siegel, a clinical professor of medicine at NYU Langone Medical Center, said he wasn't surprised by the study's findings.

"Studies have shown that people who don't get sufficient or full-quality (deep REM) sleep are more susceptible to viral infections if exposed," he said, adding that a lack of sleep "also impacts recovery time from illness."

Aric Prather, a professor of psychiatry and behavioral science at the University of California, San Francisco, said it's "well-known that sleep plays an important role in regulating the immune system."

"How that happens is not well understood, but data suggests that aspects of sleep — like slow wave sleep, or the hormones released during sleep, like growth hormones — may directly communicate with the immune system to support protection," he said.

Why men had worse vaccine response than women

Prather said he was surprised at the differences in immune response between men and women.

"There are some data to suggest that vaccines work differently in men and women, with some data to support an advantage for women, including for the COVID-19 vaccine," he said. "However, this meta-analysis suggests that men who get insufficient sleep are more likely to experience suboptimal vaccination response compared to women."

Phyllis Zee, a neurology professor and director of the Center for Circadian and Sleep Medicine at Northwestern University's Feinberg School of Medicine, noted that there are "known sex differences in immune response to foreign antigens, like viruses, and also to self antigens, like in autoimmune disorders."

"In general, women have stronger immune response, including (to the) flu vaccine," Zee said. "The evidence is that these differences reflect hormonal, genetic and environmental differences, which can change over the lifespan, so these differences may be less prominent among older adults."

According to Karine Spiegel, from the French National Institute of Health and Medicine who was lead author on the study, immunity in women "is influenced by the state of the menstrual cycle, the use of contraceptives, and by menopause and post-menopausal status, but unfortunately, none of the studies that we summarized had any data about sex hormone levels."

Would the study results apply to COVID-19 vaccines?

While the study did not cover the relationship between sleep and responses to the COVID-19 vaccines, Michael Irwin, distinguished professor of psychiatry and biobehavioral sciences at the UCLA Geffen School of Medicine and a coauthor on the study, said he believes the results would be the same.

"How we stimulate the immune system is the same whether we're using an mRNA vaccine for Covid-19, or an influenza, hepatitis, typhoid or pneumococcal vaccine," he said. "It's a prototypical antibody or vaccine response, and that's why we believe we can generalize to Covid."

The researchers performed an analysis that found that if a person showed up for a COVID-19 vaccination without enough sleep, their antibody response to the vaccine would be weakened by the equivalent of two months.

"You would have already lost two months of immunity, so to speak, even though you just got the shot," Irwin said. "If you have a poor immune response, you are less likely to get full protection from Covid." (Rudy, Fox News, 3/13; LaMotte, CNN, 3/13; Moniuszko, CBS News, 3/14)