What is a Booster Vaccine & Should I Get One?

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woman with a band aid on her arm from a vaccine

Booster shots have been part of our lives since childhood. Nearly all vaccines require a booster at some point. Chair of the UnityPoint Clinic Vaccine Committee, Dr. Stephen Rinderknecht, explains all you need to know about booster shots, including the COVID-19 booster, and why they’re so important.

Childhood Through Adulthood Booster Shots 

What is a Vaccine Booster Shot? 

During your first or primary vaccine dose(s), your body reacts by creating specialized proteins called antibodies in your blood, which recognize and eliminate the targeted foreign invader (often a virus or bacteria) should you encounter it in the future. While your immune system has an impressive ability to remember how to protect you, the antibodies from some vaccines can fade away. In those cases, immunity lessens as your antibody protection is reduced. This is where booster shots enter the picture.

What’s the Purpose of a Booster Shot?

The purpose is to boost your immune system after the initial immune response to a vaccine, or series, has dropped over time. It offers a nice reminder to the immune system about how to keep your body protected. Those who get appropriate boosters are more protected against disease than those who don’t get booster shots.

Which Vaccines Require a Booster Shot? 

Most vaccines you receive as part of the recommended CDC childhood, adolescent and adult immunization schedules require a booster shot sometime after the primary series is complete. The number of booster doses needed is based on how long immunity lasts, which has been determined over the years with the help of science. It may be as few as one booster shot (like the chickenpox vaccine), and you’re set for life-long protection. Or, some boosters are needed every 5-10 years (like tetanus and whooping cough).

What’s the Difference: Booster Shot vs. Extra Dose?

The difference isn’t in the product itself, but rather the recipient of the vaccine.

  • Booster shot. A booster shot or booster dose is needed to help improve immunity that has decreased over time. Usually there is some time the separates the primary series and the booster dose.
  • Additional/extra dose. An additional dose or extra dose is needed when the response to the primary series wasn’t strong and didn’t create enough antibodies to begin with. This is often for people with a weakened immune system (like those with cancer) who don’t respond as well to the vaccine. Often an additional dose if given closer in time to the initial doses and is considered part of the primary series in qualifying people.

Why Isn’t the Annual Flu Vaccine Called a Booster Shot?

Booster doses are the same vaccines as the original vaccine. The annual flu vaccine isn’t called a booster because it’s a different vaccine each year. The continual changes in the influenza virus structure can be slight (antigenic drift) or drastic (antigenic shift). How much change occurs from previous seasons determines how much of a threat it is each year. The World Health Organization makes an annual educated guess to determine how to best match the vaccine to the expected virus for the upcoming season.

Specifics About COVID-19 Boosters

Is the COVID-19 Booster Shot for Everyone? 

The COVID-19 booster shot is currently (as of May 2022) approved for everyone 5 and older.


Is it Safe to Mix-and-Match Brands for a Booster Dose?

The CDC authorized mix-and-match boosters based on results of several clinical study and experiences from other countries. The Pfizer, Moderna and J&J booster each demonstrated an immune response, regardless of which vaccine the participants initially received. 

However, the CDC voted that Pfizer and Moderna mRNA vaccines should be given priority over the J&J vaccine for primary and booster vaccinations. That decision was made due to the risk of blood clots associated with the J&J product. 

What’s the Different Between the Booster and the Primary COVID-19 Vaccine Doses?

The Pfizer (Comirnaty) booster shot contains the same amount of mRNA as each of the two primary doses. So, it’s the exact same thing. The Moderna booster has half of the mRNA that’s in the two primary doses, which still provides plenty of protection. The Johnson & Johnson/Janssen booster, which doesn’t contain mRNA, is no different than the primary dose.

How Long After the COVID-19 Booster Shot Does Immunity Increase?

Just like with the primary series, you’ll experience an increased immunity two weeks after a booster dose.

Are There Side Effects after the COVID-19 Booster?

You may experience side effects after your booster similar to what you experienced with the initial series. That could include a sore arm, tiredness and headache. Other reactions could include fever, chills or muscle pain.

Do I Need a Booster if I Contracted COVID-19 after the Primary Two-Dose Series?

It’s always a good idea to get vaccinated and boosted, even if you’ve experienced a breakthrough COVID-19 infection. The antibody level after vaccination is more predictable, durable and protective compared to “natural” immunity. This is evident by looking at the increased chance of reinfection after disease as compared to breakthrough infection after vaccination.

If you’ve contracted COVID-19 or knowingly been exposed, you should follow CDC guidelines for isolation or quarantine before getting your booster. That’s simply to prevent any healthcare workers from becoming ill.

Does the Booster Help Protect Me from Variants?

Yes, antibody levels are higher in those who are vaccinated and boosted than people who’ve previously had a COVID-19 infection and are unvaccinated. The strong antibody levels created by vaccination can better neutralize an attack by any variant of COVID-19, including delta and omicron.

How Many Boosters Will We Need?

The need for ongoing, regular booster doses of COVID-19 vaccines will be determined by the duration of immunity provided by the current booster, as well as the behavior of the pandemic. All of that'll be decided by the vaccine makers, the FDA and the CDC as testing and data collection continues. 

It’s possible once the world’s population develops a high state of immunity, transmission of the virus stops and the pandemic smolders and goes away. Vaccine hesitancy (in the U.S.) and lack of vaccine resources (in Africa) will prolong the process. The longer the virus can circulate, the greater the chance that virus variants will develop. If those variants are different enough to evade our current immunity, the whole cycle starts over again.