COVID-19 Vaccine FAQ

Having questions about COVID-19 vaccines is completely understandable. Medical and public health experts are still learning about COVID-19 and COVID-19 vaccines, but there is a lot we do know. Check out the below answers to some of your most common questions. 

What COVID-19 vaccines are currently being used?

Three vaccines are currently in use to protect against COVID-19 in the U.S. Two vaccines have been authorized for emergency use by the FDA: the Moderna vaccine and the Janssen Biotech vaccine. The Pfizer/BioNTech vaccine was fully approved and licensed by the FDA on August 23, 2021. The Moderna and Pfizer vaccines are mRNA vaccines and require two doses of the same vaccine three weeks apart (Pfizer) or four weeks apart (Moderna) for full protection. The Janssen vaccine is an adenovirus viral vector vaccine and requires only one dose. Learn how the different vaccines work.

Are the vaccines safe?

Yes. No corners were cut in developing safe vaccines, despite the speed at which they were developed. The authorized vaccines underwent the same rigorous approval process as other vaccines. Vaccine manufacturers are required to follow guidance issued by the Federal Drug Administration (FDA) when developing any vaccine, including COVID-19 vaccines. Each is required to provide their clinical trial data to the FDA, which the FDA and other experts use to conduct a thorough review of the vaccine’s safety and efficacy before authorizing it for use. The results of all COVID-19 vaccine clinical trials are reviewed by over 50 independent experts by the time the vaccine is authorized. The authorized vaccines will be continuously monitored through many different safety systems to ensure the vaccines' safety. Many of these systems have existed for many years and work well to ensure that the benefits of vaccination continue to far outweigh any risks. 

  • Do COVID-19 vaccines cause blood clots?
    On April 23, the Advisory Committee on Immunization Practices (ACIP) of the CDC voted to lift the pause on the use of the Johnson & Johnson COVID-19 vaccine after careful review of safety data. The vote to resume use of the vaccine comes after it was paused after reports of a rare and serious kind of blood clot in the days and weeks following vaccination. Out of the nearly 8 million J&J shots that have been given so far, CDC and FDA identified just 15 cases of these rare blood clots. The risk to your health if you get COVID-19 is serious and the benefits of the J&J vaccine far outweigh the risk of a rare side effect like this. The pause and thorough review of the vaccine's safety and efficacy proves that vaccine safety monitoring systems are working and that safety is a top priority. Experts will continue to monitor the situation to ensure the benefits of the vaccine continue to outweigh the risks. There is no concern about this adverse event in people who have received the Moderna or Pfizer vaccines. For additional information, please visit Vaccinate Your Family's website.
  • Do COVID-19 vaccines cause heart inflammation? 
    You may have heard that a small number of teens and young adults (about 140 out of 1 million doses of vaccine given) have experienced cases of mild heart inflammation, myocarditis and pericarditis, after getting an mRNA COVID-19 vaccine (Pfizer or Moderna). The cases were observed mostly in older teens and young adults, more often in males, more often after the second dose of vaccine, and within four days following vaccination. While heart issues can seem scary, myocarditis and pericarditis can be mild and treatable. The CDC has been studying these cases closely and based on the latest evidence, determined that heart inflammation appears to be an incredibly rare side effect of mRNA COVID-19 vaccines (whereas the risk of myocarditis from COVID-19 infection is much higher) and concluded that the benefits of COVID-19 vaccination outweigh the risks. People with a history of myocarditis or pericarditis can choose to consult with their doctor before getting vaccinated.
  • Do COVID-19 vaccines cause Guillain-Barré syndrome (GBS)?
    You may have heard that a small number of people (100 as of July 13) have reported developing Guillain-Barré syndrome (GBS) following vaccination with the Johnson & Johnson vaccine, out of 12.5 million doses administered in the U.S. Although the available evidence suggests an association between the J&J vaccine and GBS, it is not enough to establish a casual link. The FDA has reviewed the cases and determined that the known benefits of J&J vaccine continue to outweigh the known and potential risks. The FDA has issued a revised Johnson & Johnson (Janssen) COVID-19 Vaccine EUA Fact Sheet to include information about GBS and notes that vaccine recipients should seek medical attention right away if they develop any GBS symptoms after receiving the J&J COVID-19 Vaccine. Every year in the U.S. an estimated 3,000 - 6,000 people develop GBS and most recover fully. The FDA will continue to monitor reports of GBS following vaccination.
  • Do COVID-19 vaccines impact fertility?
    No. Scientists agree that the COVID-19 vaccines do not impact puberty or fertility in females or males, now or at any time later in life. The mRNA vaccines teach our cells to make a harmless piece of spike protein so that our body builds antibodies and can fight off future COVID-19 infections. It’s biologically impossible for those antibodies to attack other kinds of proteins that would in turn affect eggs, sperm, or cells in the reproductive organs. The Pfizer COVID-19 vaccine is safe and effective for teens. And all of the COVID-19 vaccines are strongly recommended by the CDC for pregnant people. Pregnant people who become infected with COVID-19 are 15 times more likely to die and 22 times more likely to have pre-term births than pregnant people not infected. COVID-19 vaccines are safe for pregnant people, and can drastically reduce the risk of adverse pregnancy and neonatal outcomes.

Who can receive the COVID-19 vaccine?

Everyone ages 12 and older who wants a vaccine can and should receive one. (Note: The Pfizer COVID-19 vaccine is the only vaccine currently available to children ages 12 to 18.) Read on below for specific guidance for pregnant persons, immune-compromised people, people with allergies, and young children.

I'm hearing a lot about boosters. Am I eligible for a booster dose of COVID-19 vaccine?

Some studies have shown that after getting vaccinated against COVID-19, vaccine protection against the virus may wane over time and may not be as strong, decreasing its ability to protect against infection. This lowered effectiveness is likely also due to the greater infectiousness of the Delta variant. Because of this, on September 24, the CDC recommended booster doses of Pfizer's COVID-19 vaccine for certain groups, including adults 65 and older, residents of long-term care facilities, and people ages 18-64 with underlying health conditions. They also gave the green light for booster shots for those ages 18-64 who live or work in a place that puts them at high risk for becoming infected with COVID-19. The recommendations are only for people who initially received the Pfizer vaccine as their two-dose series. Decisions about booster doses for Johnson & Johnson's and Moderna's COVID-19 vaccines have not yet been made. 

 Additionally, as of September 2, it is recommended that moderately to severely immune-compromised individuals who received an mRNA vaccine for their initial two doses of COVID-19 vaccine receive a third, additional dose of the same vaccine at least 28 days after their second dose. This additional dose is not the same as a booster dose because it is considered part of the initial vaccine series, whereas a booster is not. The CDC made this recommendation because this population is especially vulnerable to COVID-19 and may not build the same level of immunity as those who are not immune-compromised. A third dose will help immune-compromised individuals mount a better immune response to COVID-19.

Will I be required to get a COVID-19 vaccine?

Some people will be required to get a COVID-19. This depends on a variety of factors, like where you work and/or where you go to school.

  • Work Requirements
    Beginning September 20, all Colorado state employees must either be fully vaccinated against COVID-19 or submit to twice-weekly testing. All Colorado staff who work in health care facilities licensed by the state health department are also be required to be vaccinated. Federal employees and contractors will also be required to be vaccinated by November 22, with no option to instead submit to regular testing. And lastly, anyone in the U.S. working for an employer with 100+ employees will be required to get vaccinated or submit to weekly testing.
  • School Requirements
    There is currently no vaccine requirement in place for COVID-19 vaccines for Colorado K-12 schools and students. However, some colleges and universities have implemented COVID-19 vaccine requirements for students, staff and faculty. Please check with your college or university to understand their specific requirements.

Where can I get a COVID-19 vaccine in Colorado?

Coloradans ages 12 and older can receive a COVID-19 vaccine at numerous vaccination sites and clinics across Colorado. For information about where to get vaccinated in your area, visit the state health department's Where to Get Vaccinated webpage or call the vaccine hotline at 1-877-COVAXCO (1-877-268-2926). The hotline is available 24 hours a day, 7 days a week with answers available in multiple languages. 

For information about vaccine equity clinics and other pop-up clinics happening across the state, visit the Colorado Vaccine Equity Taskforce's Get Vaccinated webpage. Some vaccination sites and clinics require appointments, while others are available for walk-ups.

What do I do if I need transportation support to or from a COVID-19 vaccine clinic?

Don’t let transportation challenges stop you (or your family or friends) from getting vaccinated. Mile High United Way is providing access to free rides to vaccination sites across Colorado, Monday - Friday, 8am - 5pm, through their Ride United Program. Dial 2-1-1 or visit to learn more. 

Are the vaccines effective?

The available vaccines are very effective. In clinical trials, both the Moderna and Pfizer vaccines demonstrated over 94% efficacy with two doses. The Janssen Biotech vaccine demonstrated 85% efficacy at preventing severe cases of COVID-19 and 66% efficacy at preventing moderate and severe disease. All of the vaccines were shown to be effective at preventing hospitalizations and death due to COVID-19. However, no vaccine is 100% effective, which is why it's important to continue practicing other disease-prevention measures like wearing a mask in public, washing your hands and maintaining distance from those outside your household until enough of the community is vaccinated to offer community immunity

  • Why are some vaccinated people testing positive for COVID?
    COVID-19 vaccines are incredibly effective, but they aren’t 100%. We know from clinical trials that Modern and Pfizer are 95% effective, which is very high, but means that some people (about 4-5%) could get COVID-19 even if they are vaccinated. As of October 1, there have been ,3,519 breakthrough cases reported out of 3.2 million fully vaccinated Coloradans, which is a rate of about 0.001%. While this number may be underreported, it still signals a very high vaccine efficacy. If you do get COVID-19 after being vaccinated, your risk of getting severely ill, being hospitalized or dying is very low. In Colorado, if you are vaccinated, you are 3.3 times less likely to get COVID-19, 4.9 times less likely to be hospitalized for COVID-19, and 5.9 times less likely to die from COVID-19. All COVID-19 vaccines are nearly 100% effective at preventing severe illness leading to hospitalization and death. And since the Delta variant, which is the dominant strain currently causing COVID-19 infections, spreads more easily and quickly among unvaccinated people, there’s a lot more virus circulating, which is also contributing to breakthrough cases.

How many people were involved in the clinical trials?

Trials for all vaccines currently authorized for use in the U.S. included people from all communities to closely match the demographics of the U.S. population and ensure representation from different age groups, races and ethnic backgrounds.

In the Pfizer/BioNTech clinical trials, there were over 44,000 participants over the age of 16. The trial for 12 - 15 year olds included 2,260 adolescents. About 30% of U.S. participants in the Pfizer trials were from racial and ethnic minorities, and about 45% of U.S. participants were between 56 – 85 years of age.

In the Moderna trials, there were over 28,000 participants. 37% of participants were from racial and ethnic minorities, 7,000 participants were people age 65 and older, and over 5,000 participants were younger people with chronic diseases like obesity, cardiac disease and diabetes. 

In the Janssen Biotech trials, there were about 40,000 participants. About 20% of trial participants were 65 years and older, about 45% were Hispanic or Latinx, about 17% were Black or African American, about 8% were American Indian or Alaska Native, and about 40% had at least one medical condition like obesity or high blood pressure.

How do mRNA vaccines work?

mRNA vaccines provide a set of instructions that teach our cells how to make a piece of a spike protein that triggers an immune response in our bodies and causes it to begin making protective antibodies, just like it would if we encountered COVID-19 virus. These antibodies are then prepped and ready to fight off the virus if we are ever exposed to it -- before it causes infection. mRNA vaccines cannot make you sick with COVID-19 because they do not use the live virus that causes COVID-19. mRNA vaccines do not change or alter your DNA. Once the vaccine is done triggering our cells to create the spike protein, our cells break down the mRNA and get rid of it.

How do viral vector vaccines work?

Viral vector vaccines work by using a different virus (in the Janssen COVID-19 vaccine, this virus is called an "adenovirus") as a vector to deliver important instructions in the form of a gene to our cells. In the the COVID-19 vaccine, this gene instructs our cells to make the SARS-CoV-2 spike protein, which triggers production of antibodies and a resulting immune response. The vaccine cannot cause infection with either COVID-19 or the virus vector (adenovirus). Viral vector vaccines have been well-studied and have even been used to respond to recent Ebola outbreaks.

Which vaccine will give me the most protection?

All three vaccines currently available for public use are shown to be highly protective and effective (nearly 100% in fact) at preventing hospitalization and death due to COVID-19. All of the vaccines are effective tools for helping end the pandemic. The best vaccine is the one most readily available to you. 

Do COVID-19 vaccines protect against virus variants?

Yes. You may have heard that there are variants of the COVID-19 virus that are circulating. According to the CDC, the current vaccines available in the U.S. help protect against these variants, including one that you may be hearing a lot about called Delta. The Delta variant was first found in the U.S. in March 2021 and has since been deemed a "variant of concern" because it spreads much more easily and quickly than other variants and may cause more severe disease. As of October 1, the Delta variant is causing 99% of the COVID-19 cases in the U.S. and cases and hospitalization rates are again rising, especially in areas with low vaccination rates. Health officials have claimed that this is now a "pandemic of the un-vaccinated" as those who are unvaccinated account for about 99% of deaths and 97% of hospitalizations due to COVID-19. As a precaution to help stop the spread of the Delta variant, state and local officials may choose to require masks to help protect those who are not fully vaccinated.

Is the vaccine free? Will I have to show an ID?

Yes, the vaccine is free and no, you will not be required to show identification. No one, whether they are privately insured, on Medicaid or Medicare, or uninsured will have to pay to get the COVID-19 vaccine. Everyone, regardless of documentation status, can receive a vaccine. In Colorado, a vaccine provider should not ask to see your ID. You may need to provide basic information like name and phone number before getting your vaccine for contact purposes.

Can I take paid sick leave from my job to go get the vaccine?

Yes. In Colorado, the Healthy Families and Workplaces Act concerning paid leave rights allows employees to use supplemental public health emergency (PHE) leave to seek preventative care, including getting vaccinated, during a public health emergency.

If I have allergies, can I get vaccinated?

People with severe allergies to a COVID-19 vaccine ingredient, a previous dose of COVID-19 vaccine, or to polysorbate should not get the COVID-19 vaccines. People who have had a severe allergic reaction to other vaccines in the past should consult their health care provider before receiving the vaccine. People with severe allergies to anything else (medications, foods, bees, etc.) are allowed to get the COVID-19 vaccine, but should wait at the location the vaccine was given for 30 minutes, instead of the 15 minutes that the general population are recommended to wait.

I'm pregnant. Can I get vaccinated?

Yes. People who are pregnant or breastfeeding are strongly recommended to get vaccinated for COVID-19. According to the CDC, pregnant people who become infected with COVID-19 are 15 times more likely to die and 22 times more likely to have pre-term births than pregnant people not infected. COVID-19 vaccines are safe for pregnant people, and can drastically reduce the risk of adverse pregnancy and neonatal outcomes. Pregnant and breastfeeding persons can consult with their health care provider before being vaccinated but aren’t required to. People who are trying to get pregnant do not need to avoid pregnancy after getting a COVID-19 vaccine.

I have a weakened immune system. Can I get vaccinated?

People who take drugs to suppress their immune systems can be vaccinated so long as they do not have another condition for which vaccination is not advised. A conversation with a healthcare provider may be useful in answering patient-specific questions. As of September 2, it is recommended that moderately to severely immune-compromised individuals who received an mRNA vaccine for their initial two doses of COVID-19 vaccine receive a third dose of the same vaccine at least 28 days after their second dose. The CDC made this recommendation because this population is especially vulnerable to COVID-19 and may not build the same level of immunity as those who are not immune-compromised. A third dose will help immune-compromised individuals mount a better immune response to COVID-19. Those who received the Johnson & Johnson vaccine, are not recommended to receive a third dose of COVID-19 vaccine, however this recommendation could change.

Can my child get the vaccine?

COVID-19 vaccines have not yet been approved for use in people younger than 12 years old. The Pfizer vaccine is available to children as young as 12, and the Moderna and Johnson & Johnson vaccines are available to those 18 and older. Pfizer and Moderna are currently testing their vaccines in children ages 6 months and older, though it is not certain when the vaccine will be available to children in this age group. Estimates range from fall of 2021 to early 2022. You can still protect your younger children from COVID-19 by making sure the adults around them get a COVID-19 vaccine, and by continuing to follow public health measures like mask-wearing (when required), hand-washing and physical distancing.

I've already had COVID-19. Should I get vaccinated?

Yes. People who have previously had COVID-19 infection can and should be vaccinated. Those currently infected should wait until their illness has resolved to get the vaccine. Because reinfection with the coronavirus is uncommon in the 90 days following initial infection, people who have had recent infection can still get vaccinated but may choose to delay vaccination until the end of that 90-day period, but are not required to do so. It is unclear how long natural immunity from COVID-19 disease lasts, or if it will protect from new variants. Getting vaccinated if you've already had COVID-19 adds an extra layer of protection against reinfection.

Why should I get the vaccine?

COVID-19 vaccines are one of the best tools we have to fight the COVID-19 pandemic and help restore health and economic security for our families and communities. Getting the COVID-19 vaccine will help protect yourself, your family and your community from COVID-19. Together, we can help end the pandemic; it's up to all of us.

What's being done to ensure equitable access to the vaccine for people of color?

The pandemic has hit Black, Latinx, Native American and immigrant communities particularly hard due to systemic inequities fueled by historic racism. The vaccine will be critical for mitigating COVID-19’s continued impact on these communities. In Colorado, the Colorado Vaccine Equity Taskforce was formed to ensure that all groups – regardless of race, ethnicity, ability and other factors – have all the facts to make informed decisions about the safety of vaccines for their families, and to hold leaders accountable for ensuring access to these vaccines for all. 

How long will vaccine protection last?

It is not currently known how long protection from the COVID-19 vaccine will last. However, COVID-19 has caused serious illness and death for many people, and getting the COVID-19 vaccine is far safer than getting COVID-19 and spreading it to others. Because scientists are still researching the vaccine’s protective longevity, it is important to continue disease prevention habits like wearing a mask and physically distancing from others. Health officials have announced the potential for approval of booster doses of mRNA vaccines to "boost" the immune system and offer bolstered protection; these booster doses could roll out in September, 2021. These boosters would be recommended for individuals who received both doses of either Pfizer or Moderna's COVID-19 vaccine, 8 months after their second dose. A third dose of COVID-19 vaccine is currently recommended for immune-compromised individuals.

What are the side effects of the vaccine?

People who get the COVID-19 vaccine may experience no side effects at all. Others may experience mild side effects, which may include pain, swelling or redness at the injection site, fatigue, low-grade fever, chills or headache. These side effects are common and a sign that the vaccine is doing its job and mounting a robust immune response in your body. Experiencing side effects does not mean you have COVID-19. Remember, the vaccine cannot give you COVID-19.

What information will I need to provide in order to be vaccinated?

Your information won’t be used for anything other than vaccine distribution and follow-up information about the vaccine. Like other routine vaccinations, you will need to share some personal information with your vaccine provider when you get a COVID-19 vaccine. This may include your name, date of birth, and contact information. You do not need to be a U.S. citizen to get a COVID-19 vaccine, and you will not need to provide a government-issued ID to get the vaccine in Colorado. Your immunization records are confidential, personal medical information, and public health will never share them publicly. 

Will I need to continue wearing a mask, washing my hands and practicing physical distancing?

In August, CDC updated it's guidance on mask-wearing, recommending that everyone, fully vaccinated or not, wear a mask indoors in public if you are in an area of substantial or high transmission. Everyone is required to wear masks on planes, buses, trains and other public transit. People who are not fully vaccinated should continue to wear masks indoors everywhere and around others outside of their household. For more information on Colorado's mask requirements, visit

People who are vaccinated but have weakened immune systems should consider continuing mask-wearing and other disease prevention measures at all times, and should consult their doctor to discuss these protections. Even with new evidence about the COVID-19 vaccines' effectiveness, continuing to wear a mask even when and where one is not required is ultimately an individual choice and everyone should continue to do what is most comfortable for themselves and their families based on their risk and preference. 

For additional information and answers to other common questions, visit CDPHE's COVID-19 Vaccine FAQ.