Why You Need a Booster Even If You’re Vaccinated

Medically Reviewed by Melinda Ratini, MS, DO on October 25, 2022
4 min read

Vaccines are your best protection against serious illness from COVID-19. If you’re fully vaccinated, the chance you’ll get very sick, end up in the hospital, or die from the disease is much lower.

But studies show COVID-19 vaccines become less effective over time, especially in people ages 65 and older. In general, protection seems to wane about 2 months after a Johnson & Johnson shot and 5 months after your second Pfizer or Moderna shot.

If you’re eligible, the CDC and FDA both recommend a COVID-19 booster shot.

The goal of a booster is to restore and extend your defense against the coronavirus, including variants such as Omicron.  

But a booster isn’t the same as an “additional dose.” Additional doses are extra vaccines given to people who didn’t build much or any protection after their first shots. You might need one if you have a medical condition or treatment that weakens your immune system.

The CDC considers you to be up to date with your COVID-19 vaccines if you have completed a COVID-19 vaccine primary series and also received the most recent booster dose recommended for you.

  • The CDC bases the COVID-19 vaccine recommendations on three things:
    your age
  • the vaccine you first received
  • the length of time since your last dose. 

If you have a moderate-to-severely weakened immune system, the CDC recommends that you get an extra primary series dose if receiving the Moderna or Pfizer-BioNTech series. Your doctor can let you know what’s right for you.

According to the CDC, people ages 5 years and up should get one updated (bivalent) booster if it has been at least 2 months since their last COVID-19 vaccine dose, whether that was their final primary series dose, or an original (monovalent) booster. 

They also recommend an updated (bivalent) booster for those who have gotten more than one original (monovalent) booster.

COVID-19 vaccines are safe and effective. But talk to your doctor about the pros and cons of each kind. They’ll let you know which vaccine is right for you.

For children ages 5 and up, the CDC recommends getting the updated (bivalent) booster at least 2 months after 2nd dose of their primary series or last booster. Children aged 5 years can only get a Pfizer updated (bivalent) booster, whereas children ages 6 years and up can get either a Pfizer or Moderna booster.


Tell your doctor if you’ve tested positive or have symptoms of COVID-19. They may suggest that you delay your next vaccine dose (primary dose or booster) by 3 months from when your symptoms started or, if you had no symptoms, when you first received a positive test.
You are less likely to catch COVID-19 again in the weeks to months after infection but certain things such as if you or a close contact are at high risk for severe disease, your local COVID-19 Community Level is high, or which variant is circulating could be reasons to get a vaccine sooner rather than later.

They’ll also let you know how long you need to isolate and recover before it’s safe to get your shot.

It’s normal to have some side effects. That’s a natural sign your immune system is working to build protection against the coronavirus.

Your post-shot symptoms might be similar to the ones you had after your first or second vaccine dose. They should go away in a few days.

Common booster side effects include:

  • Redness, pain, or swelling where you got the shot
  • Fever and chills
  • Body aches and headache
  • Tiredness
  • Swollen lymph nodes in your armpit

Call your doctor if you start to feel worse.

Experts don’t advise taking medicine to prevent vaccine side effects. But you can probably use some over-the-counter drugs to feel better after getting a booster. Ask your doctor if it’s safe to take:

  • Acetaminophen
  • Antihistamines
  • Aspirin
  • Ibuprofen

Do not give aspirin to anyone under the age of 19 unless their doctor says it’s OK. It’s linked to a rare but very serious condition called Reye syndrome.

COVID-19 vaccines and boosters are available for free. But you’ll likely need to make an appointment to get one. You can go to the pharmacy or clinic that gave you your original vaccine or somewhere different.

Bring your CDC COVID-19 vaccine card with you. A health professional will update it with the date and location of your booster. If you don’t have a card, or you lost your old one, ask your pharmacy or state health department how you can get one.

Places that offer a COVID-19 booster might include:

  • Retail pharmacies
  • Hospitals or health centers
  • Walk-up vaccine clinics

If you have trouble getting to a vaccination site, a health care worker might be able to come to you. You can:

  • Contact your doctor or health provider.
  • Call the Medicare hotline at 800-633-4227.
  • Call 211 to find other health services.
  • Get help for an older loved one by calling 800-677-1116.

Check state or local health resources to find a vaccine location near you. You can also visit www.vaccines.gov or call 800-232-0233. People with disabilities can get COVID-19 vaccine info by calling 888-677-1199.

There’s evidence that COVID-19 booster shots might become less effective over time. But it’s not yet clear if that means you’ll need another dose of vaccine in the future.

Drugmakers think we might need coronavirus vaccines every year. Some are working on a single shot that’ll protect against both COVID-19 and the flu. If they’re successful, that could make yearly vaccination easier.