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COVID-19 Vaccine Frequently Asked Questions

Jestin N Carlson MD, Roya Caloia DO, FACEP, FAAEM, John Bedolla MD, Coburn Allen MD, Sameer Ismailjee MD

USACS is committed to the safety of our patients and providers. One of the most effective public health initiatives to help protect one another and ourselves is through vaccinations. There are several COVID-19 vaccines that are being developed and this page has been created to help summarize some important aspects of each.


COVID-19 FACTS





Basics & development

  • How do vaccines work?

    Vaccines work by causing your body to develop an immune response. Each time your body is exposed to either a vaccine (or virus) it creates antibodies to help fight off the infection and develops immune ‘memory’ to help fight off future infections. This immune response gets stronger each time the body comes in contact with the virus or vaccine, which is why many vaccines require at least two doses.

    immune response chart

    USACS National Director of Clinical Education Dr. Jestin Carlson describes exactly how the COVID-19 vaccination works.

  • What types of vaccines are there for COVID-19?

    The goal of the COVID-19 vaccines is to introduce some of the viral material into your body so that your body can develop antibodies to help fight the virus in the future and this can be done in several different ways. Most of the COVID-19 vaccines types are just like the ones you received during childhood. This involves injecting either an inactivated or ‘killed’ version of the virus or some of the proteins from COVID-19 inside another virus that our body can defend against referred to as a ‘viral vector’. There are also newer types of vaccines that are being tried for COVID-19 using only parts of the virus such as mRNA or DNA to create an immune response. In these cases, it is not the whole COVID-19 virus, just a small part.

  • What are the main vaccines that are being administered?

    Pfizer (mRNA), Moderna (mRNA) and Johnson and Johnson (viral vector) are being administered in the United States. On August 23, 2021, the Pfizer vaccine recieved full approval from the FDA. Both the Moderna and Johnson and Johnson vaccines are approved under Emergency Use Authorization.

  • Can you combine vaccine brands? (As in, the first shot, Pfizer; the second, Moderna?) If no, why not?

    It is not recommended to combine vaccines as the impact on efficacy is unknown.

  • What are the downsides of these vaccines?

    Minor side effects such as pain at the injection site, headache, fatigue muscle aches and 1-2 days of a fever are common. Serious side effects are very rare (<0.1%).*


    * The CDC and FDA have examined the Johnson and Johnson vaccine regarding potential concerns related to blood clots and found the vaccine to be safe and effective.
  • Why are the symptoms so severe with the second vaccine?

    Our bodies have a stronger immune response to the second dose which may contribute to the symptoms.

  • Why are they rolling the vaccine out in stages?

    Different groups of people are at different risks of complications from COVID. The vaccine is being rolled out in stages to it can get to people at higher risk.



Safety & effectiveness

  • What is different about these vaccines and are they safe?

    The Pfizer and Moderna vaccines use just a small part of the COVID-19 virus, the mRNA. This technique has been around for decades and has been shown to be safe.

    USACS National Director of Clinical Education Dr. Jestin Carlson answers the question of whether the COVID-19 vaccine is safe.

  • How effective are they?

    The vaccines have different efficacy but overall are very effective:

    • Pfizer ~ 95% effective
    • Moderna ~ 95% effective
    • Johnson & Johnson ~72% effective*
      *The Johnson & Johnson vaccine is a single injection.

    For comparison, the annual flu shot is usually 40-50% effective.

  • Are the vaccines safe in specific groups of people (children, pregnant women, people with a weak immune system)?

    The Pfizer vaccine has been approved to children as young as 12 years old. In addition, we have information from a number of other vaccines over the past 50 years showing that vaccines are safe in children and during pregnancy. Previous vaccines that only include part of the virus (mRNA and DNA) have been safely given to people with weak immune systems such as those receiving chemotherapy.

  • Do the current vaccines work against new strains of COVID-19?

    This is still being studied and there are several variants of the COVID-19 virus; however, many of the available vaccines have some efficacy against various strains of COVID-19.



Myths & misconceptions

  • Can companies track you after you have received the vaccine?

    No, they do not have the ability to track you. The FDA asks companies to perform post-market surveillance to ensure the vaccine continue to be safe. This is done with other things that the FDA approves such as when a new medication is approved.

  • Does the vaccine cause autism?

    The CDC has studied vaccines and there is no relationship between vaccines and autism.

  • Is there a microchip in the COVID-19 vaccine?

    USACS National Director of Clinical Education Dr. Jestin Carlson addresses rumors about a microchip being embedded in the COVID-19 vaccine.

  • Does the vaccine change my DNA?

    USACS National Director of Clinical Education Dr. Jestin Carlson addresses the rumor that the COVID-19 vaccine changes an individual’s DNA.

  • Was the vaccine rushed too quickly?

    USACS National Director of Clinical Education Dr. Jestin Carlson describes the development and timeline of the COVID-19 vaccination.

  • Will the vaccine cause infertility or other problems?

    USACS National Director of Clinical Education Dr. Jestin Carlson addresses the risks associated with the COVID-19 vaccine.

  • Can you get COVID-19 from the vaccine?

    USACS National Director of Clinical Education Dr. Jestin Carlson addresses concerns about whether a patient can contract COVID-19 from the Coronavirus vaccination.



Getting the vaccine

  • Who should get the vaccine?

    Right now, vaccines are approved for those 12 years and older for Pfizer and 18 years and older for both Moderna and Johnson and Johnson). The CDC recommends that almost everyone should get the vaccine including pregnant patients and those with impaired immune systems. Talk to your health care provider about the vaccine if you have more questions.

    USACS National Director of Clinical Education Dr. Jestin Carlson explains who should receive the COVID-19 vaccine.

  • Why should I get the vaccine?

    USACS National Director of Clinical Education Dr. Jestin Carlson shares why he encourages his patients to get the COVID-19 vaccine.

  • What if I already had COVID-19? Do I still need to receive the vaccine?

    The CDC still recommends that individuals get the vaccine, even if they have previously had COVID-19. While not yet proven, it is believed that the vaccine may help to reduce the chances that you may contract the virus a second time and can potentially reduce the risk of spreading the virus to others.

    USACS National Director of Clinical Education Dr. Jestin Carlson addresses the misconception that individuals do not need the COVID-19 vaccination if they already have had the virus.

  • Should I receive the vaccine if I’m pregnant?

    USACS National Director of Clinical Education Dr. Jestin Carlson explains the reasoning behind the recommendation that pregnant women be vaccinated for the COVID-19 virus.

  • What if I’m immunocompromised or have a weakened immune system? Should I still get the vaccine?

    USACS National Director of Clinical Education Dr. Jestin Carlson explains why those who are immunocompromised or have a weakened immune system should obtain the COVID-19 vaccine.

  • If a patient gets COVID between the first and second dose, is it safe to get the second dose, or should the patient wait?

    Yes, you can still get the second dose.

  • What does it mean to be 'fully vaccinated?'

    After receiving a vaccination, it takes some time for your body to develop immunity.  The term 'fully vaccinated' refers to an individual who is at least 14 days after their final dose of the COVID vaccine (14 days after the second dose of either the Pfizer or Moderna vaccine or 14 days after a single dose of the Johnson and Johnson vaccine).

    Read more from the CDC

  • What can I do after I am fully vaccinated?

    As of September 1, 2021, the CDC recommends that vaccinated individuals wear masks in crowded indoor settings in areas with high number of COVID cases or when in close contact with individuals who are not fully vaccinated.

    Read more from the CDC

  • Should I get a booster shot if I am fully vaccinated?

    At this time, the FDA only recommends boosters with either the Pfizer or Moderna vaccine for individuals with a significantly weakened immune system such as those who have had a solid organ transplant.

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