A syringe is filled with the Pfizer COVID-19 vaccine for the first immunizations offered to UCI Health frontline caregivers on Wednesday, Dec. 16, 2020.

COVID-19 Vaccine FAQ

We all want this pandemic to end. By mid-December 2020, the coronavirus has caused 75 million confirmed infections and 1.7 million deaths worldwide. More than 310,000 Americans have died due to COVID-19-related illnesses, which now exceeds heart disease as the leading cause of U.S. deaths. 

During the current winter surge, the virus is claiming about 2,500 U.S. lives every day. But safe and effective vaccines can end the pandemic if, as experts believe, at least 70% of people are vaccinated.

Two COVID-19 vaccines have received emergency approval for frontline healthcare workers and residents of long-term care homes. UCI Health infectious disease experts answer questions about these vaccines. (View the FAQ in Spanish ›)

Q. Why should I get the COVID-19 vaccine?
A. In addition to preventing infection and death by reducing your chances of getting sick, the COVID-19 vaccines also will prevent many long-lasting effects reported by COVID-19 patients. 

These include fatigue, shortness of breath, cough, muscle and joint pain, chest pain, difficulty thinking and concentrating (“brain fog”), depression, headache, and fever that comes and goes. Some people also reported heart, lung, kidney, skin, teeth and nervous system problems.

Q. Can the COVID-19 vaccines give me COVID?
A. None of the currently developed COVID-19 vaccines have the live SARS-CoV-2 virus. These vaccines cannot give you or anyone else COVID-19, nor do they make you contagious.

Q. Will I test positive for COVID-19 after being vaccinated?
A. No. The vaccine will not cause you to test positive on viral tests for COVID-19, such as PCR tests or antigen tests. However, the vaccine likely will cause you to test positive for antibody tests (also called serology) since the vaccine helps build antibodies to the virus.

Q. What COVID-19 vaccines are now available?
A. Several companies are developing vaccines that work against SARS-CoV-2, the virus that causes COVID-19. Two have been tested in large-scale clinical trials and have received emergency authorization by the FDA (Food and Drug Administration). They are:

  • Pfizer-BioNTech mRNA vaccine
    • Granted Emergency Use Authorization (EUA) on 12/11/2020
    • Large-scale trial (44,000 participants) showed 95% efficacy
    • Two-dose vaccine, requires ultra-cold storage (–70 Celsius)
    • First shipments to hospitals that can handle ultra-cold storage
    • 50 million doses to the world by end of 2020 (6.5 million to U.S.)
    • 1.3 billion doses to the world in 2021
  • Moderna mRNA vaccine
    • Emergency Use Authorization (EUA) status granted 12/18/2020
    • Large-scale trial (30,000 participants) showed 94% efficacy
    • Two-dose vaccine, requires standard cold storage (–20 Celsius)
    • First shipments to hospitals and pharmacies serving long-term care facilities
    • 20 million doses to the world by end of 2020
    • 500 million to 1 billion doses to the world in 2021

Q. Who will get the first vaccines and when?
A. The following two groups have first priority for the COVID-19 vaccine:

  • Healthcare personnel (e.g., hospitals, nursing homes)
  • Residents of nursing homes, assisted-living and other long-term care facilities

Combining the availability of both vaccines, 40 million doses are expected to be available in the United States before the end of 2020. This is enough to start two-dose inoculations in 20 million people by the end of December, with millions more to follow in 2021.

Q. When will there be enough supplies for most people to get the vaccine?
A. Vaccine manufacturing is moving at a very fast pace. Hopefully, COVID-19 vaccines will be widely available for public consumption by mid-April 2021.

In addition to the Pfizer and Moderna vaccines, several other vaccines are in current trials to be completed in early 2021. Furthermore, vaccine trials in children under age 12 have also begun.

Q. What is the difference between Emergency Use Authorization (EUA) status and full FDA (Food and Drug Administration) approval for a vaccine?
A. When an effective vaccine has been demonstrated in a trial, it can apply for EUA status with two months of post-vaccine safety data. To apply for full approval, six months of post-vaccine safety data must be provided.

The FDA is encouraging companies who receive EUA status to apply for full approval as soon as possible. Both mRNA vaccines have reported outstanding safety data with no serious side effects.

Q. What is an mRNA vaccine?
A. Many types of COVID-19 vaccines are in development. The Pfizer and Moderna vaccines are made with mRNA, or messenger ribonucleic acid that can instruct your body to make a specific protein (the spike protein) found on the surface of the SARS-CoV-2 virus.

When your body makes this virus protein, it is recognized as not human, and your body develops antibodies to it. These antibodies protect you if you encounter the virus later.

After making the protein, your body destroys the mRNA, which does not mix with your genetic code. mRNA vaccines have been used in the past for flu, rabies, CMV (cytomegalovirus) and Zika viruses.

Q. Should I worry that the vaccine was made so quickly? Were steps skipped?
A. No steps were skipped. All COVID-19 vaccines being submitted for approval must meet high U.S. safety standards. All vaccines to be distributed in the U.S. were helped by funds from the government (e.g., Operation Warp Speed), large companies or both. These funds helped speed three processes:

  • Trial enrollment — If you increase the number of staff members who are recruiting patients, you can enroll a lot of people into a clinical trial in a shorter time period. The funds helped the trials quickly enroll tens of thousands of participants.
  • Manufacturing — Funds help increase the number of available manufacturing plants, warehouses and employees. The molecular-based mRNA vaccines also can be manufactured faster because they do not require growing the virus to produce virus proteins.
  • Distribution — Funding enables the vaccines to be shipped rapidly around the nation and the world on a regular basis.

Q. How well do the vaccines work?
A. The Pfizer and Moderna COVID-19 vaccines have been tested in large trials involving more than 70,000 people. Participants were randomly assigned to two study arms, one to receive the vaccine, the other a placebo injection. They were allowed to live their lives and mix with their communities as they normally would. Since the trials are randomized, such large study groups help ensure that the type of human interactions in one study arm are similar in the other.

The trials reported a remarkable 94% and 95% efficacy in preventing COVID-19. An efficacy of 95% means the vaccine group had only 5% of the cases seen in the non-vaccine group. For example, if the placebo group had 100 cases of COVID-19, the vaccine group would have only five. The vaccine not only prevented COVID-19 cases overall, it also prevented severe cases of the disease.

Pfizer measured protection seven (7) days after the second dose; Moderna measured protection 14 days after the second dose. Summary results show:

  • Pfizer COVID-19 vaccine trial (44,000 participants)
    • 95% protection
    • All COVID-19 cases: 162 total in placebo group vs. 8 in vaccine group
    • Severe COVID-19 cases: 9 in placebo group vs. 1 in vaccine group
  • Moderna COVID-19 vaccine trial (30,000 participants)
    • 94% protection
    • All COVID-19 cases: 185 total in placebo group vs. 11 in vaccine group
    • Severe COVID-19 cases: 30 total in placebo group vs. 0 in vaccine group

Both vaccines protected well across all ages of adults studied. Trials used different age groupings when providing summary data to the FDA.

  • Pfizer
    • Ages 16 to 55: 96% efficacy
    • Over age 55: 94% efficacy
  • Moderna
    • Ages 18 to 65: 96% efficacy
    • Over age 65: 86% efficacy *

* The difference between the efficacy of Pfizer and Moderna vaccines in older adults may be due to the cut-off age for the trial. For example, it is possible that the Pfizer vaccine would have a lower protection effect had they reported data for those over age 65.

Q. Were different races and ethnicities included in the vaccine trials?
A. The people in the COVID-19 mRNA trials were of the following race and ethnicity:

  • Pfizer
    • 57% white
    • 26% Hispanic/Latinx
    • 10% Black
    • 4% Asian
    • 3% other racial groups
  • Moderna
    • 62% white
    • 20% Hispanic/Latinx
    • 10% Black
    • 5% Asian
    • < 3% other racial groups

Q. How many doses do I need?
A. Both the Pfizer and Moderna vaccines are a two-dose series. This means that you must receive both doses to achieve the 94% and 95% protection levels seen in the trials.

  • The Pfizer vaccine is two doses given 21 days apart.
  • The Moderna vaccine is two doses given 28 days apart.

Q. Am I protected as soon as I receive the vaccine? Can I stop wearing a mask?
A. No. The protection provided by the vaccine starts seven (7) days after the second Pfizer dose and 14 days occurs after the second Moderna. Until then, you should assume you have no proven benefit from the vaccine.

Even after you are vaccinated, all policies, protocols and public health orders related to COVID-19 will remain in place until you are notified otherwise.

Q. What side effects do the vaccines have?
A. So far, trials indicate that COVID-19 mRNA vaccines are highly protective and generate a strong immune response. Sometimes when vaccines produce an immune response, there may be side effects that feel like the flu. This does not mean you are infected or contagious. Instead, these symptoms are a signal that your body is successfully generating an immune response to protect you from the virus.

Data are being reviewed by the FDA and more details will become available. Here's what we know so far about side effects:

  • Pfizer mRNA vaccine
    • Any symptoms: 59% after first dose, 70% after second dose
    • Mild to moderate symptom type: fatigue 63%, headache 55%, muscle aches 38%, chills 32%, joint pain 24%, fever 14%
    • Few grade 3 (severe) side effects: fatigue 4%, headache 2%
  • Moderna mRNA vaccine
    • Limited data currently known. More data released when EUA status granted.
    • Grade 3 (severe) side effects: fatigue 10%, muscle aches 9%, joint pain 5%, headache 5%

Schedule your vaccinations when you do not have anything important planned for the next day or two, including work.

Q. If I have food or medication allergies, should I worry about an allergic reaction to the vaccine?
A. Having a significant allergy to a food or medications does not necessarily mean you are at higher risk for having an allergic reaction to the COVID-19 vaccine. The risk of an allergic reaction exists for those who have a known allergy to the vaccine (from prior doses) or a known allergy to an ingredient in a vaccine. For example, mRNA vaccines are not made in chicken eggs and there should not be any additional risk for people with known allergies to eggs.

Please consult your doctor before being vaccinated if you have many serious allergies. If you have been told to carry epinephrine (Epipen) for any reason, you should continue to do so, including at the time of vaccination.

All vaccine distribution centers must have emergency allergy medications on site. The CDC also recommends that everyone vaccinated be observed for 15, and for 30 minutes for anyone with a history of anaphylaxis. If you are unable to wait that long, we recommend being around other people for the 15 minutes or are on the phone with someone who is aware that you have just been vaccinated and knows your location.

Q. Should I take Tylenol or Motrin before my vaccination?
A. If you regularly take aspirin, acetaminophen (e.g., Tylenol) and ibuprofen (e.g., Motrin, Advil) for other medical conditions, continue to do so as directed by your physician or as needed. Otherwise, do not pre-medicate.

Taking over-the-counter medications such as acetaminophen and ibuprofen before receiving a vaccine may reduce its ability to work and blunt your immune response to the vaccine. After the vaccination, don’t hesitate to take an over-the-counter medication if you have symptoms that make you uncomfortable.

Q. What if I get the first dose then don’t want the second?
A. The Pfizer and Moderna trials were not designed to assess the effectiveness of a single shot. For example, everyone in the Pfizer vaccine group received two shots, 21 days apart. Even though overall data suggest that benefits may start after the first dose, we don’t know enough to make any conclusions.

The scientific evidence so far shows that two doses are needed to achieve 94% to 95% protection. This is why you should not start the vaccine series unless you intend to complete it.

Q. What if I missed my second dose?
A. Try to get the second dose on time. Data on vaccine benefit was based on a fixed number of weeks between doses (three weeks between Pfizer doses; four between Moderna doses). If you are late, you should still receive the second dose.

Most vaccines have rules for how many weeks you can be late before you should start the vaccine series over. For the COVID-19 vaccines, doses will be given late until the CDC or published clinical data provide guidance on when it is too late to give a second dose.

Q. If I already had COVID-19, do I need the vaccine?
A. Yes. People who have had COVID-19 should still get the vaccine. Natural immunity to COVID-19 after infection is unpredictable. The vaccine ensures you receive the same protection levels found in the trials. Vaccines should not be given to anyone who is actively infected. After full recovery, you can and should receive the vaccine.

Q. Can pregnant, breastfeeding or immunocompromised persons get the vaccine?
A. Pregnant, breastfeeding and immunocompromised persons were not enrolled in the mRNA vaccine trials so there are no data currently available to make a recommendation. While awaiting further data and guidance, we understand that pregnant or immunocompromised persons are at higher risk for more serious disease and may make the personal choice to receive the vaccine.

If you are pregnant, breastfeeding or attempting to become pregnant, you should consider your personal risk for COVID-19 based on your interactions with friends, family and the community. Second, concerns for any potential medication effects to a developing fetus are generally during the first trimester when organs are forming. Third, the mRNA in the vaccines does not cross the placenta to reach your baby. But protective antibodies you produce do pass to your baby through the placenta and breastfeeding.

The American College of Obstetricians and Gynecologists recommends that the COVID-19 vaccine be offered to pregnant and breastfeeding women, and recommends against requiring women of childbearing age to have a pregnancy test before receiving the vaccine.

The concern for immunocompromised persons is not for safety, but rather that the vaccine may not generate as strong a protective response as in persons with a healthy immune system. Nevertheless, a partial response may be an important benefit. Discuss your preferences and options with your doctor.

Q. Who pays for the vaccine?
A. At this time, the two mRNA vaccines are free because the U.S. government has purchased millions of doses. In the future, this may change: The government may purchase more doses, your insurance may cover the cost or you may be able to pay out of pocket.