Why your mood could affect your flu shot

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Silly cat videos could be good for your health – at least if you are about to get one of the seasonal vaccines.

For instance, when people who were in a positive mood got a flu shot that day, they produced higher levels of antibodies to help them fight the disease, according to one British study.

This data on mood and vaccines is limited, but a substantial body of research shows many other lifestyle factors – such as diet, exercise and even social interactions – may affect how much protection people get from vaccines, including, it appears covid-19 jabs.

Scientists are still trying to determine how higher antibody counts translate into disease protection in real life: After all, there are other parts of the immune system, such as T-cells, that play an important role in keeping us healthy, too. Yet for now, antibody levels are a common measurement used by scientists trying to determine vaccine efficacy, and “that is generally a correlate of protection,” says Marian Kohut, an immunobiologist at the Iowa State University.

Not all people respond to vaccines in the same way. Some develop better antibody protection than others, while immunization may fail for an unlucky few.

“The response induced by a vaccine can vary tremendously between individuals,” says Bali Pulendran, an immunologist at Stanford University. Age is part of the reason, he says, with older people generally responding less effectively than younger ones.

Genetics also play a role. Studies of twins show that for some vaccines, such as measles, almost 90 percent of the variation in antibody response is due to our genes (for other vaccines, these numbers are lower – for mumps, for instance, the variation in antibody response due to genes is 39 percent).

Yet even if you are older and didn’t win the genetic lottery, you can still improve your chances of a good vaccine response, experts say.

“Sleep is a biggie,” says Janice Kiecolt-Glaser, professor emeritus in psychiatry at Ohio State University’s College of Medicine whose research has focused on how stress and depression can alter our immune and endocrine systems. “When you’re not sleeping, you’re [impairing] your immune response.”

A 2023 meta-analysis of studies showed that sleeping fewer than six hours a night can hamper the immune system’s response to various vaccines.

In one experiment, where volunteers would sleep a mere four hours a night over a period of six days before vaccination, those who were sleep-deprived had only half the antibody response to their influenza vaccine 10 days after the jab compared with people who were allowed to sleep as much as they wished.

This is why Kiecolt-Glaser recommends “getting enough sleep, especially the night before, a couple of nights before ideally, and then getting enough sleep after the vaccine.”

Diet is important, too.

Research shows that a healthy gut microbiota plays a significant role in how well we respond to vaccination. In one 2023 study, among people receiving the Pfizer-BioNTech coronavirus vaccine, those who had a larger abundance of a beneficial gut bacteria associated with the eating of the Mediterranean diet – called Bifidobacterium adolescentis – maintained their vaccine protection longer, even six months after their second dose. Other research also found links between microbes that are known to keep the gut healthy and a better response to cholera vaccine and tetanus vaccine.

Antibiotics, meanwhile, can deplete the gut microbiome, potentially disturbing our immune response to vaccination – as Pulendran and his colleagues found in their 2019 study.

Taking antibiotics for five days “resulted in a 10,000-fold reduction in the bacteria in the gut,” he says. As a result, “people who got antibiotics had much, much lower antibody response to the flu vaccine than the control people.”

For Pulendran, such diminished efficacy of vaccines is “yet another reason” we shouldn’t prescribe antibiotics indiscriminately.

The good news is that probiotics seem to enhance the microbiome, including Bifidobacterium adolescentis, boosting the levels of antibodies produced after immunization. In one flu study, for example, taking Lactobacillus probiotics twice a day for 28 days after vaccination significantly increased the levels of antibodies. In mice, a Lactobacillus supplement helped the rodents’ immune response after a covid shot – although it’s worth noting that results in mice don’t always translate into humans.

Pulendran warns that such research doesn’t mean you should rush to the nearest store to stock up on probiotics.

“There is this bewildering array of different products,” he says, which have not been evaluated by science and are of mixed quality. This makes it difficult to assess what might boost the effectiveness of a particular vaccine.

Instead, Pulendran says, people should work on our healthy gut microbiome in the long term by eating plenty of fiber, while avoiding processed foods and added sugars.

In addition to sleep and diet, physical exercise appears to improve vaccine response in many people. Kiecolt-Glaser says this is why she tries to time her workouts for just before her annual flu and covid shots.

A 2022 meta-analysis suggests that a short bout of exercise right before or immediately after immunization can increase the efficacy of flu vaccines, especially in older adults.

Exercising the arm in which you get the jab might be particularly beneficial – doing biceps curls, for example, says Kohut, whose research focuses on factors that affect the immune response to viral infection or vaccines. These kinds of “muscle damaging types of exercise done in the muscle where the vaccine is being administered would induce inflammation – and having higher inflammation could improve immune response to the vaccine,” she says.

Exercise also may diminish side effects that some people experience after vaccination, such as swelling at the jab site, or fever, according to a 2018 study. And even going for a brisk walk, lasting 45 to 90 minutes, after the shot may boost the antibody response, Kohut says her research suggests.

There are several theories why exercise may improve immune function, Kohut says, such as muscle-secreted proteins that influence the immune response and exercise-induced changes in the production of metabolites – chemical compounds that the body generates during metabolism.

Yet, she admits, scientists still don’t fully understand the mechanisms linking exercise and vaccine efficacy.

As with diet, research suggests making exercise a permanent and regular feature in your life is probably the most effective way to boost your antibody response to a vaccine.

A large 2023 study of health-care workers showed that for regular exercisers, coronavirus vaccines were over 85 percent effective in preventing hospital admissions. But in sedentary people – those engaging in less than 60 minutes of moderate intensity physical activity per week – immunization was just 60 percent effective. (One caveat – regular exercisers may have had better diets or sleep.)

Exercise aside, if you are having a particularly stressful couple of days, Kiecolt-Glaser says, you may want to avoid scheduling vaccinations at that particular time, especially if you are not young.

“The older a person is, the more stress matters” for the efficacy of vaccines, she says.

Kiecolt-Glaser’s research on seniors (mean age 73) caring for a spouse with dementia showed that only 38 percent developed an antibody response to the influenza vaccine, compared with 66 percent of those in the same age group who were not caregivers.

Strong social connectedness tends to boost how well we react to vaccines, studies have found.

In one report, first-year university students – who were vaccinated against the flu and could name at least 13 close friends or family members with whom they met frequently – produced significantly more antibodies after the jab than peers who reported fewer close contacts.

Similar effects have been found in studies involving the pneumococcal vaccine and covid shots – people with better social networks appear to have a stronger antibody response than those who were lonelier or had few connections.

It may be a little late in this winter’s vaccine cycle to focus on addressing loneliness, nurturing relationships with neighbors or modifying your gut microbiota. But ensuring a good night’s sleep, sidestepping vaccinations on high-stress days and taking a brisk walk post-jab could all be advantageous.

And if silly cat videos make you relaxed and happy just before a shot, maybe that will help, too.