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Am I eligible for a booster shot? Your COVID-19 vaccine questions answered

Missouri amended its standing order for the Pfizer COVID-19 vaccine last week to make it available for those who qualify for a booster shot. 

But what is the difference between a booster shot and a third dose? Does the booster shot come with side effects? Is it safe for pregnant people? 

We asked Missouri’s health officials to answer readers’ questions on the COVID-19 vaccine boosters. Here are their responses based on CDC guidance. 

Is the booster shot available in Missouri? Who is eligible for it? 

First, it is important to note the different authorizations. There are those eligible for a third dose who are immunocompromised (this happened in mid-August), and there are those who are eligible for a booster. Eventually, we expect all individuals who have been vaccinated to become eligible for boosters.

A third dose of the Pfizer (12 and up) or Moderna (18 and up) vaccines may be administered 28 days after a second dose to moderately to severely immunocompromised people due to a medical condition or combination of immunosuppressive medication or treatments including but not limited to the following:

  • Immunocompromised due to solid organ transplant and taking immune suppressing medications
  • Immunocompromised due to active treatment for solid tumor and hematologic malignancies
  • Immune compromised due to Receipt of CAR-T cell or hematopoietic stem cell transplant (within 2 years of transplantation or taking immunosuppression therapy)
  • Moderate to severe primary immunodeficiency (eg., DiGeorge, Wiskott-Aldrich Syndromes)
  • Immunocompromised due to Advanced or untreated HIV infection
  • Immunocompromised due to “Active treatment with high-dose corticosteroids or other drugs that may suppress immune response: high dose corticosteroids (ie.,≥ 20 mg prednisone or equivalent per day), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor-necrosis (TNF) blocker or other biologic agents that are immunosuppressive or immunomodulatory”

Missourians 18 and up who received the Pfizer vaccine can receive a booster shot at least six months after their initial series based on CDC guidance:

  • People 65 years and older and residents in long-term care settings should receive a booster;
  • People aged 50–64 years with underlying medical conditions should receive a booster;
  • People aged 18–49 years with underlying medical conditions may receive a booster; and
  • People aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting (e.g. frontline medical workers, teachers, and first responders) may receive a booster.

The list of medical conditions categorized as high-risk by the CDC is available here

When will people who received the Moderna or Johnson & Johnson vaccines be eligible? 

More data on the effectiveness and safety of Moderna and Johnson & Johnson booster shots are expected in the coming weeks. The CDC has committed to keeping the public informed with a timely plan for Moderna and Johnson & Johnson booster shots.

If I’m eligible for a booster shot, does this mean I’m no longer safe after getting the other two doses? 

The COVID-19 vaccines approved and authorized in the U.S. continue to be effective at reducing risk of severe disease, hospitalization, and death. Experts are looking at all available data to understand how well the vaccines are working for different populations.

Is the booster shot safe? Are there side effects? 

Yes, serious side effects are rare. Most reported side effects from boosters have been similar to that of the two-shot series (fatigue, pain at injection site).

Can I mix vaccines (ex: I got Moderna initially, can I now get the Pfizer booster)?

Those who received the Moderna or Johnson & Johnson COVID-19 vaccines are not yet eligible for a booster shot, but we do expect this to change fairly soon for Moderna. Currently, the CDC recommends sticking with the same vaccine brand you originally received when possible. However, third doses for immunocompromised individuals are an exception. “For [immunocompromised] people who received either Pfizer-BioNTech or Moderna’s COVID-19 vaccine series, a third dose of the same mRNA vaccine should be used,” the CDC states. “If the mRNA vaccine product given for the first two doses is not available or is unknown, either mRNA COVID-19 vaccine product may be administered.”

Will we always need booster shots every few months/years? 

We do not know at this time, but we learn more each day about how long vaccines provide protection to people, both those who are healthy and immunocompromised.

If I’m eligible, where can I get a booster shot? 

Boosters are available anywhere vaccines are currently available. Keep in mind that those getting third doses due to being immunocompromised must have had their series of Moderna or Pfizer and should get the same manufacturer if possible. Those getting a booster should’ve had their series of Pfizer six months prior and should get the same vaccine for their booster dose. Visit to find a vaccine.

How much will it cost me? 

COVID-19 vaccination is completely free. Americans cannot be charged anything for the vaccine or administration of the shot.

I’m pregnant and qualify for a booster shot. Is it safe? 

Yes, pregnancy is considered a factor that puts an individual at high risk for becoming severely ill with COVID-19. Pregnant and recently pregnant people (for at least 42 days following end of pregnancy) are more likely to get severely ill from COVID-19 compared with non-pregnant people, and we encourage these women to get vaccinated.