Flu season is coming and many of us will be getting a flu vaccine. It’s recommended everyone older than 6 months gets a flu shot, with a few rare exceptions. But did you know that you can make the flu shot more effective just by getting it at the right time?
Getting your flu vaccine at the right time of year will keep you protected at key points of the flu season, and getting your shot at the right time of day can boost how many antibodies your body makes, meaning you’re better protected from the virus.
Below, we’ll dive into the best time of day and year to get the flu jab, as well as other simple things you can do to boost how effective it is.
Looking to book your seasonal flu shot appointment? Opt for a morning time slot if possible. Research suggests getting your flu jab in the morning may make it more effective compared to getting it in the afternoon.
This is because of your circadian rhythm, or your internal biological clock. Your circadian rhythm runs on a roughly 24-hour cycle and dictates everything from when you feel awake and sleepy, when your body produces certain hormones, and when your body temperature rises and falls throughout the day and night.
And it turns out your circadian rhythm also has an impact on how your body reacts to vaccines, drugs, and treatments.
When it comes to jabs, a 2016 study looked at whether the time of day of vaccination changed older adults’ immune responses to the flu vaccine. The researchers analyzed vaccines given between 9 a.m. and 11 a.m. and those given between 3 p.m. and 5 p.m. One month after vaccination, they looked at patients’ antibody responses to three different flu virus strains.
They found that in two out of three different virus strains, the antibody response was higher when the vaccine was administered in the morning compared to in the afternoon. There was no difference for the third strain of influenza virus.
Dr. Anna Phillips, the principal investigator of the study said, “We know that there are fluctuations in immune responses throughout the day and wanted to examine whether this would extend to the antibody response to vaccination. Being able to see that morning vaccinations yield a more efficient response will not only help in strategies for flu vaccination, but might provide clues to improve vaccination strategies more generally.”
Older adults are less able to produce antibodies due to their aging immune systems, and they’re the age group most likely to be hospitalized or killed by flu, so getting the timing right is even more important in this population.
The researchers said this difference between morning and afternoon flu shots could be down to the fact that the immune system responds differently to challenges depending on the time of day, so the timing of vaccination can impact how well your immune system creates antibodies.
Heads-up: If you can’t get a morning appointment for whatever reason, getting the flu shot at a less-than-ideal time is better than not getting it at all.
It’s not just the flu shot. An earlier study by the same researchers found men’s immune response to both the flu shot and hepatitis A vaccine was better in the morning than in the afternoon.
Although the same wasn’t found in women, the researchers did note this study had a smaller sample size and it looked at both younger and older patients. Both men and women showed greater immune responses to the morning flu shot in the 2016 study.
Beyond hepatitis A, one 2021 study found morning COVID vaccines were more effective than afternoon vaccines. But there is some conflicting research here (more on that soon).
Morning may not be best for all vaccines, however. In the 2016 study we mentioned above, the researchers stated: “It is possible that the best time of day for vaccination may be different for different vaccines, as they stimulate different types of immune response for protection.” More research needs to be done.
Delivering a drug or treatment at a time that’ll make it more effective based on your circadian rhythm is called chronotherapy. Beyond vaccines, researchers are finding there’s a right time to do everything from undergoing open-heart surgery to getting chemotherapy.
Even medications are impacted by your circadian rhythm. A 2017 paper found, “the tolerability of nearly 500 medications varies by up to fivefold according to circadian scheduling.”
Your circadian rhythm affects how effective a drug is because it determines:
Even getting the correct diagnosis can depend on the time of day. According to Russell Foster and Leon Krietzman in Rhythms of Life, an asthma diagnosis can change throughout the day. Potential asthmatics get the function of their airways tested, but this is usually higher in the afternoon compared to the morning. So, getting an early-morning doctor’s appointment could help asthmatics get the right diagnosis.
Why isn’t chronotherapy more mainstream? Well, there is some pushback from some medical professionals, and hospital treatments often need to be administered at a time that suits the shift work staff (think cancer treatments).
When at home, you’re told to take a drug at a set time each day, but this is usually to try to increase compliance rather than efficacy. Plus, it’s hard to work out the circadian rhythm of individual patients and how each treatment or drug will be affected.
While the RISE app can’t tell you when to get open-heart surgery or an asthma diagnosis exactly, the app can predict your circadian rhythm each day and show you when your body naturally wants to wake up, go to sleep, and when your energy levels will fluctuate throughout the day.
Beyond chronotherapy, knowing how to work with your circadian rhythm can help with everything from boosting your energy levels to falling asleep faster at night. RISE guides you through 20+ daily sleep hygiene habits and tells you the ideal time to do them each day based on your own circadian rhythm.
RISE users on iOS 1.202 and above can click here to set up their 20+ in-app habit notifications.
For your flu shot to be the most effective you need to get it at the right time of year, as well as the right time of day. Ideally, aim to get your shot before seasonal influenza starts spreading.
After getting a flu shot, it takes about two weeks to reach full immunization, or for your body to reach peak levels of antibodies. So, you should get the flu shot before the end of October.
However, you don’t want to get it too early, either. The protection slowly wears off, so you don’t want to be left more vulnerable towards the end of flu season and get sick then.
It’s advised that those who have a higher risk of flu complications — like older people, pregnant women, or those with asthma or heart disease — or those living in places with high flu activity should get their flu shots as soon as possible.
Those who aren’t at high risk of serious complications and who live in a low-flu-activity place may want to wait until later in the influenza season, so they’re protected later into the year.
For example, your risk of catching flu is lower during fall than in winter, so you may want to wait until early winter to get vaccinated, so your protection doesn’t drop off towards the end of the season.
But, as with the time of day, getting it at the less ideal time of year is better than not getting it at all. You’ll still have some protection if you get it “too early” in the year, and getting it “too late” will at least protect you for the rest of the winter.
As well as getting it at the right time, here’s what to do to boost how effective your flu shot is.
Sleep debt is the running total of how much sleep you owe your body. It’s measured against your sleep need — the amount of sleep you personally need — and in the RISE app, we calculate sleep debt over the last 14 nights.
So, if your sleep need is 8 hours 30 minutes, but you’ve only been getting 7 hours of sleep lately, you’ll have built up a lot of sleep debt.
One study suggests the average sleep need is 8 hours 40 minutes, plus or minus 10 minutes or so, but 13.5% of us may need 9 hours or more sleep a night.
RISE users on iOS 1.202 and above can click here to view their sleep need.
RISE users on iOS 1.202 and above can click here to view their sleep debt.
What’s this got to do with the flu shot? Well, when we’re sleep deprived our immune systems don’t work as well as they should. High sleep debt doesn’t just impact your mood, productivity, and energy levels, your response to flu vaccinations is affected, too.
And it doesn’t take a lot of sleep deprivation to have an effect, either. One study looked at two groups of participants. One group had four hours of sleep for six nights, followed by seven nights of 12-hour nights of sleep to recover. They got vaccinated in the morning on their fourth day. The other group got enough sleep before and after their vaccination.
After 10 days, the results showed the antibody levels in the sleep-deprived group were less than half of those in the group who were getting enough sleep.
Antibody levels were equal three to four weeks after vaccination, however. But, antibody production was compromised at first in those with sleep debt, even though participants had those 12-hour-long recovery sleeps.
Getting enough sleep after a vaccine can also boost its effectiveness. Research found participants who had a normal night of sleep after a hepatitis A vaccine had almost twice as many antibodies as participants who stayed awake the night after getting the vaccine.
You don’t need to miss a whole night of sleep to get an impaired antibody response though. Shorter sleep duration has been found to result in lower antibodies after a vaccine compared to longer sleep durations.
So, when you’ve booked your flu shot, start paying more attention to your sleep debt in the lead-up to the jab and afterward.
The RISE app works out how much sleep debt you have and keeps track of it as you pay it back. We recommend keeping this number below five hours to feel your best, and to give your flu shot a chance at maximum effectiveness.
In the run-up to your flu shot (and any other time), you can pay down sleep debt by:
Having low sleep debt will not only boost how effective the flu shot is, it’ll reduce your chances of getting ill with flu — as no vaccine is 100% protective. Having low sleep debt will also protect you from other illnesses, like the common cold and COVID.
When you’re living out of sync with your circadian rhythm, your energy levels take a hit and you increase your risk of everything from obesity to depression to cancer.
You might be out of sync if:
You don’t just have one circadian rhythm to deal with, though.
You have your master clock, controlled by a central pacemaker called the suprachiasmatic nucleus, which is found in the hypothalamus region of your brain. This master clock controls things like your sleep-wake cycle, hormone production, and body temperature fluctuations.
It also communicates with other clocks throughout your body. These body clocks are called peripheral clocks and they’re present in almost every organ group and tissue, including your metabolism, your digestive system, and — you guessed it — your immune system.
Your immune system runs on a cycle. At certain times, it’s more alert and ready to attack bugs when you’re more likely to encounter them. And at other times, it’s ready to stand down when it’s not needed, which reduces the chances of the immune system attacking itself.
But when we’re sleep deprived and not living in sync with our circadian rhythm, the immune system’s timing gets thrown off, making you more vulnerable to illness and meaning you take longer to recover, too.
To make sure your immune system is working as it should get in sync with your circadian rhythm. Here’s how:
RISE users on iOS 1.202 and above can click here to see their circadian rhythm on the Energy screen.
Light exposure is not only great for waking you up, it may increase how effective the flu vaccine is.
A 2021 study looked at older adults with dementia and whether the amount of daytime light exposure they got affected their response to the flu vaccine. The results showed that those who got more light exposure during the day had “significantly greater” levels of antibodies after the vaccine compared to those who got less light exposure.
The researchers concluded: “Increasing daily light exposure may have beneficial effects on the human immune system, either directly or via circadian rhythm stabilization.”
While this study was on older adults with dementia, the benefits of light may help anyone after a flu vaccine. So, aim to get more daytime light exposure after your flu shot by going for a long walk, taking your workout outside, or working by a window.
Getting light exposure as soon as possible after waking up will also help to reset your circadian rhythm, keeping you in sync. The RISE app can remind you when to get light in the morning and when to avoid it in the evening.
RISE users on iOS 1.202 and above can click here to set up their Bright Light Control Habit.
Most of the time, flu jab side effects are mild and should clear up within a day or two.
Common side effects include:
Compare this to the common flu symptoms of fever, chills, sore throat, sneezing, a cough, headaches, fatigue, and generally feeling like you can’t get out of bed for a week, and they don’t sound so bad.
A flu illness can be a much more serious illness, too. The respiratory illness kills half a million people worldwide each year, and those with pre-existing health conditions are at risk of developing complications.
The pandemic isn’t over, so beyond an influenza vaccine, a COVID vaccine or booster should also be on your list. But the COVID-19 vaccine, and indeed COVID-19 itself, is relatively new, more research needs to be done to see if the time of day affects this jab.
For example, a 2021 study found antibody levels were higher when people were vaccinated in the afternoon compared to the morning. But a different 2021 study found antibody levels were higher in those vaccinated in the morning. More recently, an April 2023 study suggests the best time to get the COVID vaccine is around midday or between 10 a.m. to 2 p.m. (with the correlation found to be the strongest in children and teenagers, as well as adults over 50). This same study says the least favorable vaccination timeframe is 4 p.m. to 7 p.m.
So clearly, more research needs to be done on the coronavirus vaccine. But, just like with flu, getting the vaccine at a less-than-ideal time is better than not getting it at all.
Heads-up: It is safe to get your flu shot and your COVID booster at the same time. You may feel a few more side effects, but these should be mild.
Research suggests your body will produce more antibodies after a morning flu shot than an afternoon one. And the best time of year to get it would be before flu starts spreading if you’re vulnerable, and a little later in the season, to extend how long you’re protected for, if you’re not vulnerable.
To make your flu shot even more effective, use the RISE app to lower your sleep debt before your jab, keep it low afterward, and get in sync with your circadian rhythm. Bonus: doing these things will help you feel and perform your best each day, even when flu season has passed.
The best time of day to get a flu shot may be in the morning. Research suggests you’ll produce more antibodies after a morning flu shot compared to after an afternoon one.
The best time of year to get a flu shot is before flu starts spreading, so in fall or early winter. If you’re at risk of flu complications, get vaccinated earlier. If you’re not, consider waiting a little longer to get vaccinated so you’re protected later into the flu season, as protection from the vaccine wears off over time.
If you don’t get a flu jab in fall or early winter, it’s not too late to get one later in the year. You’ll still be protected for the rest of the flu season, which can sometimes extend into spring.
According to the Centers for Disease Control and Prevention (CDC), everyone over six months of age should get a flu jab. People with severe allergies to ingredients in the flu jab should not get the vaccine, and those with an egg allergy or those who have Guillain-Barré syndrome should talk to a healthcare professional before getting the flu vaccine.
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