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How Do I Know If I Need a COVID-19 Booster Shot?

Jan. 6, 2022 - Katie McCallum

With COVID-19 cases rising, now is the time to get boosted if you're eligible.

But you might be wondering whether you and other members of your family actually need a COVID booster or not and, if you do, how to go about actually getting one.

Everyone 12+ is now eligible for a booster, but not everyone is eligible immediately. This varies based on which vaccine you received and how far out you are from your initial dose or doses.

Dr. H. Dirk Sostman, chief academic officer of Houston Methodist, is here to answer common questions you may have about getting an additional dose.

Three quick clarifications before we get started:

  • If you or your child (5+) are moderately or severely immunocompromised, you are eligible for a third dose after 28 days have passed since your second shot of Pfizer or Moderna. You're eligible for a booster after your third dose, as well.

  • If you're unvaccinated, get your first dose as soon as possible.

  • If you're unvaccinated and you've recently tested positive for COVID-19, find out how soon you can get vaccinated after recovering from COVID-19.

Are booster shots actually necessary?

A booster is an additional dose of vaccine that can help prolong protective immunity in someone who responded fully at first, but there's evidence that protection is declining after some time.

"In essence, it's a 'top-up' of a person's antibody-mediated immune response to the first vaccine series," says Dr. Sostman. "Circulating antibodies are the first line of defense against getting infected or becoming ill if you are infected." 

Boosters are being recommended because data is showing that protection against mild and moderate COVID-19 via the initial vaccine series declines over time — particularly for those who were vaccinated some time ago. Added to that is the concern about the new COVID-19 variant, omicron.

Fortunately, Pfizer, Moderna and J&J have all announced that laboratory studies indicate that booster doses of these vaccines offer protection against omicron.

(Related: Will We Need More Booster Shots in the Future?)

Who is eligible for a booster shot?

The eligibility criteria for a COVID booster are admittedly confusing.

The simplest place to start, though, is to consider:

  • Your age
  • Which vaccine you initially received
  • How far out you are from your initial dose or doses

COVID Booster Eligibility:

People Who Are Immunocompromised (Ages 5 & Up)

Individuals who are moderately or severely immunocompromised are eligible for a third dose after 28 days have passed since his or her second shot of Pfizer or Moderna.

A person is considered immunocompromised if he or she:

  • Is actively being treated for a solid tumor or blood cancer
  • Has received a solid-organ transplant and is taking immunosuppressive medications
  • Has received a stem cell transplant in the last two years
  • Is actively being treated with certain immunosuppressive medications, including high-dose corticosteroids
  • Has a moderate or severe primary immunodeficiency, such as DiGeorge and Wiskott-Aldrich syndromes
  • Has advanced or untreated HIV infection

This applies to anyone who is 5+, although 5 to 17-year-olds are only eligible to receive an additional primary dose of the Pfizer vaccine, as this is the only vaccine authorized for use in children of this age group.

People Who Received Pfizer 5+ Months Ago (Ages 12 & Up)

Anyone who is 18 years of age or older and received the Pfizer COVID-19 vaccine at least five months ago is eligible for a booster dose of any available vaccine.

Teens 12-17 years of age who were vaccinated at least five months ago are eligible for a booster dose of Pfizer.

People Who Received Moderna 6+ Months Ago (Ages 18 & Up)

Anyone who is 18 years of age or older and received the Moderna COVID-19 vaccine at least six months ago is eligible for a booster dose of any available vaccine.

People Who Received Johnson & Johnson 2+ Months Ago (Ages 18 & Up)

Anyone who is 18 years of age or older and received the J&J vaccine at least two months ago is eligible for a second dose of any available vaccine.

If you don't meet these criteria, you may still be able to get a Pfizer booster shot via a doctor-prescribed dose.

Because Pfizer's COVID-19 vaccine is fully approved by the FDA, your doctor can choose to prescribe the Pfizer vaccine as a booster, based on his or her best judgment for off-label prescribing. Off-label means the vaccine is being administered outside of the FDA's fully approved guidelines. It is very common for many different medications to be prescribed in this manner.

In addition, the FDA and CDC have also authorized the use of heterologous (or “mix and match”) booster doses for people who 18 years of age or older, meaning you can receive a booster of Pfizer even if it wasn't your primary vaccine series.

How do you know if you actually need a booster? Do your antibody levels matter?

"If you're eligible for a booster but aren't convinced you need another dose, consult your doctor. He or she can help you make a decision based on your individual benefits and risks of getting an additional dose," adds Dr. Sostman.

One such way your doctor may choose to help make this decision is to check your antibody levels, also called antibody titers. There are many components to immunity, and antibodies are an important one — especially in the early stages of infection.

"COVID-19 vaccination elicits robust antibody production in most people, but the levels of these antibodies wane over time," explains Dr. Sostman. "If you're unsure whether you need a booster, your antibody titers can be one piece of information your doctor uses while counseling you on your decision. If your titers are very low, a booster shot may be recommended. However, we do not recommend routine use of titer measurements."

Can you mix and match vaccines during your booster?

If you are 18+, you are able to choose which vaccine you receive as a booster dose if you meet the criteria above for a such a dose.

For these adults, the known and potential benefits of receiving a different vaccine as a booster dose outweigh the known and potential risks of mixing and matching.

Do you still need a booster if you've recently had COVID-19?

COVID-19 immunity is complicated, especially for those who have both natural immunity (from recent infection) and vaccine-induced immunity. Understanding how these two might work together and whether protection can be additive has yet to be answered.

"We know that having COVID-19 can elicit an increase in antibodies that protect you from re-infection with the virus, so there's likely some time in which natural immunity can act as a 'booster'," says Dr. Sostman.

He points out that we don't know how long this might last, though, so eventually you will still need an actual booster shot.

"In addition, there is some data suggesting that COVID-19 infection followed by vaccination may provide extremely strong immunity, but we just do not have enough data to know whether this can substitute for a vaccine booster shot," he adds.

If you have recently had COVID-19 and are eligible for a booster, it's recommended that you get your shot after your symptoms have resolved and the recommended time has elapsed since your primary series of either Pfizer (5 months), Moderna (6 months) or J&J (2 months). People who received monoclonal antibodies as part of their COVID-19 treatment plan will need to wait 90 days before getting a COVID booster.

How do you actually get your COVID booster?

Get Your COVID-19 Vaccine or Booster
Everyone 5+ can receive a COVID-19 vaccine and those who are 12+ may be eligible for a booster. We offer walk-ins and online scheduling for free Pfizer vaccines.
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