How Helpful Is Being Hydrated Before You Get a COVID-19 Vaccine or Booster Shot?

Here's what to know—especially if you're prone to fainting.

You're probably well aware that the COVID-19 vaccine typically comes with at least a few less-than-pleasant side effects such as pain at the injection site, fever, and fatigue. However, feeling any discomfort at all isn't exactly how you want to spend the day after getting vaccinated.

To help, some pharmacies are offering up tips on what you can do before and after your COVID-19 shot to help reduce symptoms.

RiteAid suggested people "eat a nutritious meal and hydrate" before their vaccine appointment to "potentially lessen any side effects." CVS, too, urged people to "drink at least 16 ounces of water [one] hour before your appointment to help prevent side effects," in a reminder email before their vaccine appointments.

Why Do Providers Say to Drink Water Before/After COVID shot?
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But how much of a role does hydration—especially hydration from drinking water—play in alleviating discomfort from getting a COVID-19 vaccine? Here's more about the link between the two.

What Does It Mean To Be Hydrated—And Why Is It Important?

Being hydrated means that you have enough fluid in your body for the different systems to work properly so that you don't end up dealing with the effects of dehydration.

"Good hydration is great for general bodily function," said William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine. Specifically, drinking enough water helps your heart pump blood easily and your muscles work efficiently.

The Centers for Disease Control and Prevention (CDC) also stated that water helps in the following ways:

  • Maintaining a normal temperature
  • Providing joint lubrication and cushion
  • Protecting sensitive tissues, such as your spinal cord
  • Ridding the body of wastes through methods such as perspiration

Furthermore, proper hydration varies from person to person and can depend on health conditions (e.g., diabetes or heart disease), if a person sweats more than usual, or if a person has been prescribed diuretics, which are medications that cause the body to lose fluids.

So, Can Being Hydrated Lessen Side Effects Following a COVID-19 Vaccine or Booster?

Dr. Schaffner explained that "…there's no specific data to suggest that drinking 16 ounces of water or anything else will, in any way, enhance your immune system or specifically ameliorate side effects." But staying hydrated isn't usually a bad thing in any situation.

The CDC recommends that those who get the vaccine stay well hydrated after the vaccine if they end up developing a fever as a side effect. But they don't specifically advise people to drink a certain amount of water either before or after the vaccine to help prevent side effects.

CVS, however, does suggest drinking water before your vaccine for a specific reason: to help decrease the chances of a person fainting while getting the shot.

"We added the recommendation to drink water to our vaccination appointment reminder emails in April due to some incidences of fainting we observed during the administration of a COVID-19 vaccine," said CVS spokesperson Matt Blanchette. "Increasing intravascular volume by hydrating can help prevent a vasovagal syncope [loss of consciousness] event that can lead to fainting. The CDC has also identified fainting after immunization as a concern."

Specifically, the CDC says that "giving patients a beverage, a snack, or some reassurance about the procedure has been shown to prevent some fainting" but adds that "studies are being done to look more into these strategies."

"People are more likely to faint when they're dehydrated," said infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security.

And though Dr. Adalja insisted that his thought on fainting and dehydration was purely speculation on his part, Dr. Schaffner agreed. "It's possible that, if you were better hydrated, you'd be less likely to feel woozy," Dr. Schaffner added. Past that, water isn't terribly likely to help prevent side effects, per se.

What Else To Know About Being Hydrated Before and After Vaccinations

Still, while water likely won't be a preventative method for any post-COVID-19 vaccine side effects, it may make you feel better in general—and that may translate into feeling a bit better if you do happen to develop side effects.

"It's just ideal to be well hydrated when getting a vaccine in terms of how one feels post-vaccine," Dr. Adalja said. If you happen to get the vaccine while you're dehydrated, for example, "you will feel worse and possibly get more dehydrated," Dr. Adalja added.

Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo, agreed. "It makes sense that you'd want to be well hydrated if you developed symptoms like a fever," Dr. Russo said, adding that dehydration can also "exacerbate a headache." Still, Dr. Russo stressed that "there is no data to support that this will help with the COVID-19 vaccine."

A Quick Review

There is no evidence to back up the claim that staying hydrated will lessen the side effects of a COVID-19 vaccine shot or booster.

But staying hydrated, in general, is important for your body. For example, the experts interviewed speculated that proper hydration might prevent you from fainting after a vaccine, or it can help with side effects like fever.

Regardless, Dr. Russo said drinking a good amount of water before your vaccine "can't hurt"—so there's really no reason not to down a glass before your shot, just in case.

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  1. Centers for Disease Control and Prevention. Possible side effects.

  2. Rite Aid. Pre-COVID-19 vaccination guide.

  3. Centers for Disease Control and Prevention. Water and healthier drinks.

  4. American Heart Association. Stayed hydrated—staying healthy.

  5. Centers for Disease Control and Prevention. Fainting after vaccination.

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