COVID-19 Vaccine FAQ

Below are answers to commonly asked questions about COVID-19 vaccination. All answers are reviewed by Denver Health physicians. To schedule your vaccination appointment, visit our Vaccination page or call our appointment center at 303-436-7000.

Watch our latest informational videos about the COVID-19 vaccines on our YouTube playlist.

Vaccine Distribution and Timeline FAQ

Q: When can I get the vaccine?

Everyone in Colorado over the age 12 is eligible to receive the COVID-19 vaccine. As the vaccine becomes available to the general public there is likely to be a high demand, so we cannot guarantee when you may receive your vaccination. Current vaccine distribution guidelines can be found on the CDPHE website

Q. How can I get the vaccine?

Denver Health has simplified the process to get a COVID-19 vaccine appointment. Now, you can simply go to DenverHealth.org/CovidVaccine to get to our direct scheduling platform. You can choose to schedule through your existing MyChart account or simply schedule as a “guest.” You will be able to select a location by vaccine manufacturer or to simply choose the first available appointment that fits your schedule. Please remember anyone ages 12-17 must register for a Pfizer vaccine appointment. All adults 18 and over can sign up for any available vaccine appointment or type.

If you are unable to self-schedule a vaccine appointment online, you can call 303-436-7000 to be connected to our call center for scheduling. Due to high demand there may be a significant wait. Please schedule online if you are unable to make an appointment by phone. 

This process is only for people scheduling their first dose as part of a complete vaccination.

Q: I’ve heard about different COVID vaccines. Which one will I get from Denver Health?

Denver Health is using three vaccines: one from Pfizer, one from Moderna and a third from Johnson & Johnson. All three vaccines from Pfizer, Moderna and Johnson & Johnson are safe and effective. The Pfizer and Moderna vaccines are very similar vaccines in terms of how they work and how effective they are. The FDA issued full approval for the Pfizer COVID-19 vaccine for adults 16+, meaning it is now only under the Emergency Use Authorization for teens (12-15). 

 Both Pfizer and Moderna vaccines require 2 doses given approximately 3 (Pfizer) or 4 (Moderna) weeks apart. All patients must receive the same type of vaccine for both doses, and Denver Health will help keep track of which one you receive and can schedule your appointment for the second dose as soon as you have received your first. The Johnson & Johnson vaccine requires only one dose and works in a slightly different way but produces an immune response to the same COVID spike protein as Pfizer and Moderna.

Patients who are 12-17 years old will be offered the two-dose Pfizer vaccine, as that is the only vaccine approved for use in this age group.

 

Q: Can I choose which vaccine I am going to receive?

When you make your appointment online, you can select a location by vaccine manufacturer or simply choose the first available appointment that fits your schedule. Patients who are 12- 17 years can only register for the two-dose Pfizer vaccine, as that is the only vaccine approved for use in this age group.

 

Q: Can I get my vaccine at my regular doctor’s office?

If you are a Denver Health patient, you will be able to get your vaccine at your regular clinic. When making your appointment for the first dose of the vaccine, you will receive information on where it will be scheduled, and you will be given an appointment time. It is extremely important to be on time for these appointments.

Q: Why am I not able to schedule beyond a certain date?

Scheduling is limited based on the allotment of vaccines we currently have available. More appointment options will be added as we get additional doses of vaccine.

Q: Can I just call the appointment center to schedule my appointment?

If you have MyChart, you can choose an appointment at your convenience online. We will also be able to send you appointment reminders and automatically schedule your second vaccine dose as soon as the first dose is complete. Find out more about setting up a MyChart account here.

If you do not have access to MyChart, you can sign up as a guest through the link at DenverHealth.org/CovidVaccine. If you are unable to do so online, you are welcome to set up an appointment with the Denver Health vaccine hotline at 303-436-7000. Wait times may be long as volume has increased, but we want to help get your appointment scheduled as soon as possible.

Q: How do I sign up to get the vaccine if I am 12-17 years old, or if I have a child who is 12-17 years old?
Denver Health has simplified the process to sign up for a COVID-19 vaccine appointment. Now, you can simply got to DenverHealth.org/CovidVaccine to get to our direct scheduling platform. You can choose to schedule through your existing MyChart account or simply schedule as a “guest.” You will have the choice of vaccine appointments by location and open time slots. Please remember anyone ages 16-17 must register for a Pfizer vaccine appointment, as that is the only vaccine approved for use in this age group. They will also be required to have a parental consent form signed at the time of vaccine administration.

Q: Will I still need to wear a mask after I am vaccinated?

The CDC has guidelines for vaccinated individuals. If you are fully vaccinated, you can resume activities that you did prior to the pandemic, without wearing a mask or physically distancing, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance. For now, masks are still required on planes, trains, buses and other forms of public transportation.

Q: Are there plans to provide proof of vaccination for those who get it? I can envision this becoming something that airlines will request or foreign governments may ask for in order to permit entry once travel resumes.

Yes, we are going to be handing out vaccine cards to everyone at the time of vaccination, which you should keep as proof that you received the vaccine and which one you received. There will be a place on the card for the second dose of the Pfizer and Moderna vaccines so you should bring the card to your second dose if you are receiving these as well. If the card is lost, information about the vaccine you received will also be saved in your medical record.

Q: Will I have to pay for the vaccine?
No, at this time all doses are being paid for by the U.S. government. Your insurance carrier may be billed for an administration fee, but you should not receive any bill.

Q: Do I need to be a U.S. citizen to get a vaccine?

Whether you are a U.S. citizen or not, we are all in this together. If you would like a vaccine, you will be able to get one according to what vaccine phase you are in. An ID should not be required for access to the vaccine. State and local public health agencies will never share your information for any immigration or law enforcement purposes. Receiving the COVID-19 vaccine will not count against you in any public charge determinations.

COVID-19 Vaccine Safety and Efficacy FAQ

Q: Are the vaccines safe?
The three current vaccines were administered to well over 100,000 people in large studies who have been closely monitored over several months for any adverse events. All three vaccines have been very carefully evaluated by the FDA prior to authorizing their use and they all appear to be very safe. Additionally, safety of these vaccines will be evaluated on an ongoing basis among people in the clinical trials as well as in the general public.

The Johnson & Johnson vaccine has been associated with a very small risk of a rare but serious clotting disorder called Thrombosis with Thrombocytopenia Syndrome (TTS). This has occurred in a small number of younger women after receiving the Johnson & Johnson vaccine. While Denver Health paused vaccination with this product for several days, we are now restarting its use based on updated FDA and CDC recommendations.

Q: How effective are these vaccines?
Initial results of studies of the Pfizer and Moderna vaccines show that the vaccine decreased the risk of getting sick with COVID-19 by about 95%. In addition, for people who received the vaccine but did get COVID-19, the infections tended to be less severe.  The reduction in cases in the Johnson & Johnson trial was lower than the 95% which has caused some confusion, but the most important finding from the Johnson & Johnson trial was that it appeared to be 100% effective at preventing hospitalization and death, and that trial was conducted in several countries where newer variants were circulating compared to the Pfizer and Moderna trials which were largely conducted in the US.

Detailed information about each vaccine can be found on the CDC’s COVID-19 vaccine website.

Q: What are the side effects of these vaccines?
It is important to recognize that part of why these vaccines work so well is that they cause a strong immune response, which can cause people to feel unwell for a day or so after the vaccine. For some, this is described as feeling like they have a hangover, and it is more common after the second dose of vaccine. In the Pfizer and Moderna studies, the most common side effects include soreness, redness, or swelling around the injection site, fatigue, body aches, or headache. These reactions can be treated with ibuprofen (Motrin, Advil) or acetaminophen (Tylenol) if needed. The side effects in the Johnson & Johnson vaccine were very similar, though of course they only occurred once since there is only one dose required.

Q: Should I take acetaminophen or an anti-inflammatory (for example, ibuprofen) before getting the vaccine to prevent side effects?

No. In the studies of these vaccines, these medications were not allowed prior to vaccination as they could possibly lessen the immune response to the vaccine.

Q: How long does the protection of the vaccine last?

We don’t know at this time. The studies have followed people who received the vaccine for almost 6 months now without any evidence that the protection is wearing off. The hope is that the protection will be long-lasting, but it is possible that we will need booster shots in the future. We will have more information about this in the coming months.

Q: Do I really need the second dose of the Pfizer and Moderna COVID-19 vaccines?

Both the Pfizer and the Moderna vaccines were studied as two doses – Pfizer as two doses separated by 21 days and Moderna separated by 28 days—so the information we have about how well these vaccines work is based on people receiving both doses.

Q: What happens if I get only one dose of Pfizer or Moderna vaccine?

The FDA and CDC state that both doses are needed for full immunity and no one should consider themselves protected with only one dose. You may not develop protection, or your partial immunity may also go away after some time and you could still be at risk for contracting severe disease associated with COVID-19. Thus, it is essential to get your second dose as soon as it can be scheduled. At the same time, because there are limited doses available, it is possible that the scheduling of a second dose may be delayed by up to a few weeks; this is ok as long as the second shot does happen.

Q: Will the vaccines protect against the variants of the virus from South Africa, the UK and Brazil?

Several strains of coronavirus that have several mutations that help it spread more easily from person to person have been identified around the globe and these are now commonly found in the US. In addition to being more easily spread, there is some concern that some of these variants may also cause more severe disease and can infect people who were infected with the original strain. Fortunately,  scientists believe that the current vaccines will work against this strain and probably the best strategy we have to control these strains and prevent new ones from emerging is to get the population vaccinated as quickly as possible with any of the available vaccines.

Q: Do you need to quarantine from family if you receive the vaccine?

No. There is no active virus in any COVID vaccine so quarantine after receiving the vaccine is not necessary.

Q: Can the vaccines cause COVID-19? How do they work?
The Pfizer and Moderna vaccines do not contain the whole virus so they cannot cause COVID-19. The vaccines consist of mRNA that cause your body to make a protein that is on the surface of the virus and your body makes an immune response to this protein. The vaccine is basically telling your immune system what to watch out for and to be prepared to respond quickly if it ever sees the real thing. “mRNA” often makes people think of “DNA” and wonder if the vaccines interact with our genes: they do not! mRNA works in a completely different part of our cells. The Johnson & Johnson vaccine is made using a cold virus that has had its ability to replicate removed. All the vaccine virus can do is make copies of the COVID spike protein for your body to recognize, and it is eliminated from the body after a short time.

Q: I have heard about severe allergic reactions to the vaccine. What do I need to know about that?

Severe allergic reactions were not observed in the vaccine studies but have occurred in a small number of individuals since the vaccine has been administered more widely. These events occurred in people with a history of severe allergy reactions. We are asking everybody who has had a severe allergic reaction (including to food or medications) that required medical treatment to stay in the post-vaccine waiting area for 30 minutes after the vaccine and to inform our staff immediately if any worrisome symptoms arise.

Q: Is there any risk because of the extreme cold that the Pfizer vaccine requires for storage?

No. This vaccine must be fully thawed to room temperature in order to prepare it for administration. While the long-term storage needs of this vaccine vary from those we normally administer, once the vaccine is brought to normal temperature range and prepared, the administration process is the same as other vaccines.

 

 

Who Should Get the COVID-19 Vaccine?

Q: Should I get the COVID-19 vaccine if I have recently been given another vaccine?

There is little data about the safety and efficacy of COVID-19 vaccines when given too closely to another vaccine type. Therefore, it is recommended that the COVID-19 vaccine series should be given at least 14 days before or after administration of any other vaccine. Exceptions may be made at times where the benefit or need for vaccination would outweigh the possible, yet unknown, risks of taking them too close together – for example, a tetanus vaccine as part of wound management or a hepatitis A vaccine given to contain an outbreak. If a COVID-19 vaccine is administered within 14 days of another vaccine, doses do not need to be repeated for either vaccine.

Q: If I am or might be pregnant, should I get the COVID vaccine?

Pregnant women are at increased risk of severe disease when they get COVID-19 and the FDA and CDC have stated that pregnant women may receive the Pfizer, Moderna or Johnson & Johnson vaccines. However, because the trials did not enroll pregnant women, at the present time it is not possible to say if there are additional safety concerns for pregnant women, or if the vaccine will work as well as it does in people who are not pregnant. There are no specific reasons to believe that an mRNA vaccine like the Pfizer or Moderna COVID vaccines or the adenoviral vector vaccines like the one from Johnson & Johnson would pose a risk to a pregnant woman or the fetus, but any certainty about safety in pregnancy will have to wait for future study. There is no evidence that any of the COVID-19 vaccines have any impact on fertility.

If you are or might be pregnant, you are encouraged to discuss with your doctor if you have questions; CDC information is also available here.  It is not necessary to have a pregnancy test before receiving your vaccine.  It is recommended that pregnant women avoid medications such as ibuprofen (Advil, Motrin) or Naproxen. Therefore, if you are or might be pregnant, it is important that you only use acetaminophen (Tylenol) for any symptoms that might arise after vaccination.

Q: Is the vaccine safe if I am breastfeeding?

Breastfeeding mothers were not enrolled in the Pfizer, Moderna or Johnson & Johnson vaccine studies, and therefore we do not know with certainty the safety of the vaccine in this scenario or any impact on lactation. However, there is no specific reason to suspect that the vaccine or any of its components would enter breast milk or be harmful to your baby. If you have questions or concerns, you are encouraged to speak to your doctor; further information is also available from the American Academy of PediatricsCDC information is also available here.

Q: Can I receive the vaccine if I am immunocompromised?

The COVID-19 vaccine was not studied in immunocompromised individuals, though the vaccine studies did have some participants with HIV infection. While it is not expected to be harmful to individuals who are immunocompromised, we do not yet know if it will be as effective in this population.  Because each immunocompromised patient can have different health issues, we recommend that those who are immunocompromised discuss the risks and benefits with their primary care provider. CDC information is also available here.

Q: Should I get vaccinated if I already had COVID-19?

Yes. The CDC currently recommends vaccination for people who have had COVID-19 as long as they have fully recovered and are no longer required to self-isolate.

Q: Can I receive the vaccine if I have a severe penicillin allergy? What about eggs?

Yes. There is no cross-reactivity between the penicillin antibiotics and the vaccine. The Pfizer and Moderna vaccines are not manufactured using eggs so can be received by those with egg allergies.

Q: Is it recommended to administer the COVID vaccine to any person who has received the flu shot this season?

Yes, everyone who received the flu shot can get the COVID vaccine.

 

Vaccine Development FAQ

Q: Are there pediatric vaccines coming?

According to the Food and Drug Administration, the Pfizer vaccine can be given to people 12 years and older. The Moderna and Johnson & Johnson vaccines are only for adults 18 years and older. There are ongoing studies involving younger children and infants so we may learn more about how well they work and if they are safe in that age group.

Q: How many COVID-19 vaccines are currently under development?

As of March 30, more than 20 vaccines have begun and six have completed large-scale (Phase 3) clinical trials around the world and have been authorized in some countries. There are nearly 70 vaccines in various earlier stages of development. In addition to the Pfizer, Moderna and Johnson & Johnson vaccines, a few others have already been authorized in other countries, including the AstraZeneca vaccine in the United Kingdom.

You can keep track of which trials are going on and where they stand from several websites. Here are two good examples:

https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html

https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html

Q: How do I report a problem or bad reaction after getting a COVID-19 vaccine?

The CDC and FDA encourage the public to report possible adverse events to the Vaccine Adverse Event Reporting System (VAERS). This national system collects these data to look for adverse events that are unexpected, appear to happen more often than expected or have unusual patterns of occurrence. Learn about the difference between a vaccine side effect and an adverse event. Reports to VAERS help the CDC monitor the safety of vaccines.

The CDC has also developed an additional way of communicating concerns about vaccine adverse reactions called V-safe. V-safe is a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after you receive a COVID-19 vaccination. Through V-safe, you can quickly tell CDC if you have any side effects after getting the COVID-19 vaccine

Q: What are the ingredients in the vaccines?

The Pfizer and Moderna vaccines have a simple formulation and contain few ingredients, including the mRNA, a lipid capsule that protects the mRNA until it reaches our cells, sodium and potassium salts and other buffers to balance the pH to match our bodies, and sugars to help the vaccine stay effective at room temperature. Links to the precise ingredients in the Pfizer and Moderna vaccines are available.

The Johnson & Johnson vaccine contains the replication-incompetent viral vector as well as some preservatives and buffers to keep it stable at lower temperatures. The link to the precise ingredients for Johnson & Johnson is here.

Q: Why are there two doses for the Pfizer and Moderna vaccines?

Many vaccines require multiple doses, such as those for pneumonia, Hepatitis B and measles/mumps/rubella (MMR)--all require multiple doses to ensure full immunity. The first shot shows the immune system a piece of the virus which stimulates an initial immune response. The second shot is the booster, allowing the immune system to fully develop responses that are both effective and long-lasting.  The Johnson & Johnson vaccine was able to produce high levels of antibody after only one dose which is why for now a second shot is not needed. There is an ongoing study to see if a second dose of the Johnson & Johnson vaccine gives additional benefit, and there are also studies to see if only one dose of the Pfizer or Moderna vaccine will be enough.

COVID-19 Vaccine Myths

1. Myth: COVID-19 Vaccines impact fertility.

Q: Is it safe for me to get a COVID-19 vaccine if I would like to have a baby one day?
Yes. If you are trying to become pregnant now or want to get pregnant in the future, you may get a COVID-19 vaccine when one is available to you.
There is currently no evidence that COVID-19 vaccination causes any problems with pregnancy, including the development of the placenta. In addition, there is no evidence that fertility problems are a side effect of any vaccine, including COVID-19 vaccines.
Like all vaccines, scientists are studying COVID-19 vaccines carefully for side effects now and will continue to study them for many years. 

2. Myth: COVID-19 Vaccines will alter my DNA. 

Q: Will a COVID-19 vaccine alter my DNA?
No. COVID-19 vaccines do not change or interact with your DNA in any way.
There are currently two types of COVID-19 vaccines that have been authorized and recommended for use in the United States: messenger RNA (mRNA) vaccines and a viral vector vaccine. Both mRNA and viral vector COVID-19 vaccines deliver instructions (genetic material) to our cells to start building protection against the virus that causes COVID-19. However, the material never enters the nucleus of the cell, which is where our DNA is kept. This means the genetic material in the vaccines cannot affect or interact with our DNA in any way. All COVID-19 vaccines work with the body’s natural defenses to safely develop immunity to disease. 

3. Myth: If I get a vaccine, I’ll also get COVID-19.

Q: Can a COVID-19 vaccine make me sick with COVID-19?
No. None of the authorized and recommended COVID-19 vaccines or COVID-19 vaccines currently in development in the United States contain the live virus that causes COVID-19. This means that a COVID-19 vaccine cannot make you sick with COVID-19.

COVID-19 vaccines teach our immune systems how to recognize and fight the virus that causes COVID-19. Sometimes this process can cause symptoms, such as fever. These symptoms are normal and are signs that the body is building protection against the virus that causes COVID-19. Learn more about how COVID-19 vaccines work.
It typically takes a few weeks for the body to build immunity (protection against the virus that causes COVID-19) after vaccination. That means it’s possible a person could be infected with the virus that causes COVID-19 just before or just after vaccination and still get sick. This is because the vaccine has not had enough time to provide protection. 

4. Myth: Receiving the vaccine will make me magnetic.

Q: Can receiving a COVID-19 vaccine cause you to be magnetic?
No. Receiving a COVID-19 vaccine will not make you magnetic, including at the site of vaccination which is usually your arm. COVID-19 vaccines do not contain ingredients that can produce an electromagnetic field at the site of your injection. All COVID-19 vaccines are free from metals such as iron, nickel, cobalt, lithium, and rare earth alloys, as well as any manufactured products such as microelectronics, electrodes, carbon nanotubes, and nanowire semiconductors. In addition, the typical dose for a COVID-19 vaccine is less than a milliliter, which is not enough to allow magnets to be attracted to your vaccination site even if the vaccine was filled with a magnetic metal. 

5. Myth: COVID-19 Vaccines were funded by individuals wishing to track Americans every move. 

Q: Do the COVID-19 vaccines contains controversial substances or implants such as microchips or tracking devices?
No. The first two COVID-19 vaccines to be authorized by the FDA contain mRNA and other, normal vaccine ingredients, such as fats (which protect the mRNA), salts, as well as a small amount of sugar. These COVID-19 vaccines were not developed using fetal tissue, and they do not contain any material, such as implants, microchips or tracking devices.  

6. Myth: 5G mobile networks can spread COVID-19

Q: Can viruses spread through radio waves/mobile networks?
Viruses cannot travel on radio waves/mobile networks. COVID-19 is spreading in many countries that do not have 5G mobile networks.
COVID-19 is spread through respiratory droplets when an infected person coughs, sneezes or speaks. People can also be infected by touching a contaminated surface and then their eyes, mouth or nose. 

7. Myth: The COVID-19 vaccines don’t work on new strains of the virus.

Q: Will getting the COVID-19 Vaccine protect me against all new variants?
Some new variants have been shown to spread more easily or cause more severe illness. The good news is that the current vaccines protect well against the variants circulating in Colorado, such as the U.K. (B117) variant. Scientists are still studying how well the COVID-19 vaccines work against the different variants found around the world. 

8. Myth: I’ve already had COVID-19, I don’t need the vaccine. I’m immune.

Q: If you’ve already had COVID-19 is a vaccine effective to prevent re-infection?
Yes, vaccination regardless of previous COVID-19 infection is effective in combating severe disease. An individual can be re-infected with COVID-19 even after recovering from a natural infection. Early evidence suggests that natural immunity from COVID-19 may not last very long. Therefore, it is recommended that even people who have had COVID-19 should be vaccinated.

9. Myth: COVID-19 vaccines interact negatively with other medications. 

Q: Can I get the COVID-19 vaccine if I am taking other medications?
Yes, you can still get the COVID-19 vaccine if you are taking medications. Although vaccines and medications can sometimes affect each other, these interactions don’t usually cause problems. People with a variety of medical conditions were included in the Pfizer, Moderna, and Johnson & Johnson vaccine trials. 

10. Myth: COVID-19 vaccines are not safe for people with substance use disorders. 

Q: Can I get the COVID-19 vaccine if I misuse substances?
Yes, the Centers for Disease Control and Prevention (CDC) encourages people with underlying medical conditions, including substance use disorders, to be vaccinated against COVID-19. No safety issues have been reported linking substance use to adverse reactions to any of the COVID-19 vaccines available to consumers in the United States. 

11. Myth: The side effects of the COVID-19 vaccines are dangerous and not worth the shot.

Q: What are the side effects of vaccination and are they worse than just getting COVID-19?
The COVID-19 vaccines can have side effects, but the vast majority are very short term and not serious or dangerous. The vaccine developers report that some people experience pain where they were injected; body aches; headaches or fever, lasting for a day or two. These are signs that the vaccine is working to stimulate your immune system. In contrast, getting COVID-19 can cause a prolonged illness, hospitalization, and even death.

If you have allergies — especially severe ones that require you to carry an EpiPen — discuss the COVID-19 vaccine with your doctor, who can assess your risk and provide more information about if and how you can get vaccinated safely. 

 

Vaccine Booster Shot FAQ

Who is eligible for a booster shot of the Pfizer series?

- 65+ years and older
- 18+ who have underlying medical conditions
- 18+ who work in high-risk settings
- 18+ who live in high-risk settings

Can I receive a booster shot if I received the Moderna vaccine?

Yes, but only if you are immunocompromised.

None immunocompromised individuals will need to wait until full FDA/CDC approval.  

Can I receive a booster shot if I received the Johnson and Johnson vaccine?

No, the FDA has not approved Johnson and Johnson booster shots for healthcare workers yet. We will update you when this changes. 

Can I receive the influenza vaccine on the same day as the Pfizer booster vaccine?

Yes! The CDC has updated their guidance on the timing of the COVID-19 vaccine. You no longer need to space out the COVID-19 vaccine from other vaccines. You can get more than one vaccination at the same time. 

Will additional booster shots be needed every year? 

We don’t know the frequency with which booster shots will be necessary. We will update you as we obtain more information. 

Do I need to wear a mask after receiving a Pfizer booster shot?

Yes, we require all employees to wear a mask when indoors at Denver Health due to the continued high levels of COVID-19 in the community. 

How much additional benefit does the Pfizer booster shot provide to me?

In a large nationwide study, a third dose of the Pfizer vaccine given at least 5 months after completion of the initial two dose series resulted in an 11-fold decreased risk in developing confirmed COVID-19 infection 12 days or more after the booster compared to vaccinated persons who did not get the booster in person age 60 or older. In this same study the rate of developing severe COVID-19 was reduced 20-fold with boosters.1 A smaller study showed a 5-fold increase in effective antibody levels after a booster dose in persons age 18-55. 2 The increase in effective antibody levels was even higher for those over age 65. 

How long do I need to be monitored after my booster vaccine?

A period of monitoring is recommended after all vaccines, however, persons who have had their initial COVID-19 vaccination series without a serious reaction (rash, hives, swelling or trouble breathing) are not required to stay in the vaccination area after the booster. 

Should I expect even worse side effects after the booster shot?

While everyone is different and it is impossible to predict for the individual, in a small study2 of a third Pfizer COVID-19 vaccine given about 8 months after the initial series, rates of adverse events were similar, but not worse, than those seen after the second shot.