Ask the Geriatrician: The COVID-19 Vaccine


Timothy Farrell, MD Timothy Farrell, MD
Associate Professor of Medicine and Adjunct Associate Professor of Family Medicine, University of Utah School of Medicine
Physician Investigator, VA Salt Lake City Geriatric Research, Education, and Clinical Center

The highly infectious SARS-CoV2 virus has caused the worldwide spread of COVID-19, a disease that causes mild to severe respiratory illness.  According to the World Health Organization, this worldwide pandemic has sickened more than 273 million people and more than 5 million people have died of the disease. As of December 2021, over 50 million people had been diagnosed with COVID-19 and more than 802,000 people had died from the virus in the United States.

As of August 2021, the U.S. Food and Drug Administration (FDA) has provided full authorization for the Pfizer-BioNTech vaccine and emergency use authorization for the Moderna and Johnson & Johnson/Janssen (J&J) vaccines. Moderna has applied for full FDA authorization, and Johnson & Johnson expects to apply by the end of 2021.  All three vaccines proved in clinical trials to have efficacy at preventing people from getting sick with COVID-19 symptoms. To date, over 203 million Americans have been fully vaccinated.

If you feel like the news you read about the COVID-19 vaccination seems to change daily, you’re not alone. That’s why we asked Timothy Farrell, MD, a geriatrician and Associate Professor of Medicine at the University of Utah School of Medicine, about how he answers his patients’ questions. Here, he shares his expertise with us. [Click on the plus sign to open the text for each topic below.]

Vaccine Development

Q. What are vaccine trials and why should we trust them?

A. First, it’s important to understand that safety has been key to the development and approval process for COVID-19 vaccines.

Tens of thousands of people participated in carefully designed and controlled clinical trials of COVID-19 vaccines. These trials determined how safe and effective the vaccines are. Following the completion of those trials, the U.S. Food and Drug Administration (FDA) and independent, expert advisory boards reviewed the clinical trial data to make sure that the data are correct.

Q. Who was included in the vaccine trials?

A. Currently, three vaccines have completed a phase 3 clinical trial (a late-stage trial to determine effectiveness and monitor adverse reactions in participants) in the U.S. and received FDA Emergency Use Authorization. The FDA issues an emergency use authorization only if the benefits of a vaccine outweigh its risks. Under an emergency use authorization, vaccines are still considered investigational. As of August 2021, Pfizer-BioNTech vaccine has received full FDA authorization, so it is no longer considered investigational.

The Pfizer-BioNTech COVID-19 vaccine (now also known as Comirnaty) began a phase 3 clinical trial in late July 2020 and enrolled some 44,000 participants worldwide. Approximately 42 percent of the global participants and 30 percent of US participants have racially and ethnically diverse backgrounds. In addition, 41 percent of the global and 45 percent of U.S. participants were 56 to 85 years of age. The results of the study were consistent across age, gender, race, and ethnicity demographics.   (See the FDA’s Pfizer-BioNTech fact sheet for recipients and caregivers here.)

The Moderna Covid-19 vaccination began a phase 3 clinical trial (known as the COVE study) in October 2020 and enrolled some 30,000 US participants ages 18 and older, including those at high risk for severe complications of COVID-19 disease. The COVE study includes more than 7,000 Americans over the age of 65. It also includes more than 5,000 Americans who are under the age of 65 but have high-risk chronic conditions, such as diabetes, severe obesity, and cardiac disease, that put them at increased risk of severe COVID-19. These medically high-risk groups represent 42 percent of the total participants in the Phase 3 COVE study. The study includes more than 11,000 participants from communities of color, representing 37 percent of the study population, which is similar to the diversity of the U.S. at large. This includes more than 6,000 participants who identify as Hispanic or Latinx, and more than 3,000 participants who identify as Black or African American.

According to the results published in The New England Journal of Medicine, people who received two doses of the Moderna vaccine, taken 28 days apart, reported no major side effects. In people over 65 years of age, the Moderna COVID-19 vaccine was over 86 percent effective against COVID-19.  (See the FDA’s Moderna fact sheet for recipients and caregivers here.)

There is an additional vaccine, from Johnson & Johnson/Janssen (J&J). Their vaccine phase 3 trial, known as the ENSEMBLE trial, enrolled 43,783 adult volunteers in the U.S., Latin America, and South Africa. The global participants were 59% White/Caucasian, 45% Hispanic and/or Latinx; 19% Black/African American; 9% Native American and 3% Asian. In the United States, the participants were 74% White/Caucasian, 15% Hispanic and/or Latinx; 13% Black/African American; 6% Asian, and 1% Native American.

Forty-one percent of participants in the study had conditions that raised the risk for serious COVID-19 disease, including obesity, type 2 diabetes, high blood pressure, and HIV.  The protection provided by the vaccine was similar across race and age groups, including adults over 60 years of age. (See the FDA’s Johnson & Johnson fact sheet for recipients and caregivers here.)

All three vaccines are highly effective against getting severe COVID-19.

Q. Did the vaccine trials investigate variants?

A. All three vaccine trials investigated how well the vaccines worked to protect people from the variants of COVID-19 that were active at the time. The Delta and Omicron variants had not yet developed at the time the initial trials were conducted, so they were not studied then. However, scientists have since studied the effectiveness of the vaccines against the Delta variant. All three vaccines provide  effective protection against serious illness and death from most variants of COVID-19, including the Delta variant. The Johnson & Johnson vaccine prevents fewer COVID-19 hospitalizations, ICU admissions, and death than mRNA vaccines (Pfizer-BioNTech or Moderna).  Vaccine effectiveness against the Omicron variant is under investigation.

Vaccine Administration

Q. How many shots do I need to get in order to be vaccinated?

A. The Pfizer-BioNTech and Moderna vaccines require two shots. The Pfizer-BioNTech shots are administered 21 days apart, while the Moderna shots are administered 28 days apart. The Johnson & Johnson vaccine only requires one shot. Booster shots are also available for all 3 vaccines; see below for more details. The CDC currently recommends receiving an mRNA vaccine (Pfizer-BioNTech or Moderna) instead of the Johnson & Johnson vaccine due to the severity of safety issues with the Johnson & Johnson vaccine and higher vaccine effectiveness of mRNA vaccines compared with the Johnson & Johnson vaccine.

Q.  I am immunocompromised. Do I need an additional dose of the vaccine?

A. In August 2021, the CDC recommended that people who received the Pfizer-BioNTech or Moderna COVID-19 vaccines and who are moderately to severely immunocompromised should receive an additional dose of the same vaccine that they originally received. This shot should be given after 28 days from the second dose of the Pfizer-BioNTech or Moderna vaccines. Since the first two shots may not provide full protection for immunocompromised people at the time of administration, the additional doses can increase their level of protection against COVID-19. For people who received the Johnson & Johnson vaccine, the CDC does not recommend an additional primary dose. 

Q. Are there any updates on whether I will need a “booster” shot?

A. A booster shot is another dose of a vaccine that is given to someone who has built enough protection after vaccination, but whose protection decreased over time. This is unlike immunocompromised people, who may not build enough protection after initial vaccination.

As of December 2021, the CDC recommends booster shots for all adults 18 and over who have already been fully vaccinated. Older adults in particular are encouraged to receive a booster shot. 

For those who received Pfizer-BioNTech & Moderna

It is recommended that all adults 18 and over receiver a booster shot, to be administered at least 6 months after receiving the second dose of the vaccine. The booster shot may be any of the three approved vaccines; the Moderna booster is a half-dose of the amount received in the first two shots.

For those who received Johnson & Johnson

Anyone 18 years old or older who received the Johnson & Johnson vaccine should receive a booster shot at least 2 months after receiving their second dose. The booster shot may be any of the three approved vaccines.

Mix and Match Boosters

The CDC says that people can “mix and match” booster shots. That means that you can receive a booster dose from a different manufacturer than your initial dose. For example, if you received a Pfizer-BioNTech shot for your initial vaccination, you can receive a Moderna or Johnson & Johnson vaccine for your booster dose.

Q.  As an older adult, which vaccine should I get?

A.  The CDC recommends that individuals receive an mRNA vaccine: Pfizer-BioNTech or Moderna.  In most situations, Pfizer-BioNTech or Moderna COVID-19 vaccines are preferred over the Janssen COVID-19 vaccine for primary and booster vaccination due to the severity of safety issues with the Janssen vaccine and higher vaccine effectiveness of mRNA vaccines compared with the Janssen vaccine.  However, the most important thing is that you receive the vaccine that is available to you. Receiving a vaccine will provide you with protection against the most serious COVID-19 symptoms. (If you receive the Pfizer-BioNTech or Moderna vaccine, the second dose should be from the same manufacturer as the first dose. Booster shots do not have to be from the same manufacturer, however.)

Q.  Is it safe to receive the Johnson & Johnson (J&J) vaccine?

A. In April 2021, the distribution of the J&J vaccine was put on “pause.” This is because six people who received the J&J vaccine developed a rare condition that causes blood clots with low platelets. In response, the FDA and CDC paused the use of the J&J vaccine to further investigate its safety.

This blood clot condition (thrombosis with thrombocytopenia syndrome, or TTS) is also very rare. The cases that occurred were at a rate of 7 per 1 million vaccinated women between 18 and 49 years old. For women 50 years and older and men of all ages, this adverse event is even more rare.

While these cases all occurred in younger women, older adults who have received the Johnson & Johnson vaccine should look out for symptoms of blood clots with low platelets for 3 weeks after their shot. These include:

  • Severe or persistent headaches or blurred vision
  • Shortness of breath
  • Chest pain
  • Leg swelling
  • Persistent abdominal pain
  • Easy bruising or tiny blood spots under the skin beyond the injection site
If you experience any of these symptoms, seek medical attention immediately.

Additional cases of TTS due to the Janssen vaccine have been documented since the pause including 8 deaths. There were only 2 cases of TTS and no deaths in person 65 years and older.  The FDA added a contraindication that the Johnson & Johnson vaccine should not be administered to individuals with a history of thrombosis with thrombocytopenia following the Johnson & Johnson COVID-19 vaccine. The CDC recommends, in most situations, that the Pfizer-BioNTech or Moderna COVID-19 vaccines are preferred over the Johnson & Johnson COVID-19 vaccine for primary and booster vaccination.

You may also view the FDA Fact Sheet for the Johnson & Johnson vaccine here for more information.

Q. I have heard that the three vaccines have different effectiveness rates. Will I have less protection against COVID-19 if the vaccine I receive has a lower effectiveness rate?

A. Vaccines have two roles in protecting you. The first is preventing you from contracting COVID-19 at all. In the clinical trials, when neither the Delta nor Omicron variant were circulating, the Pfizer-BioNTech vaccine was found to be 95% effective at preventing COVID-19 infection, the Moderna vaccine 94% effective, and the Johnson & Johnson vaccine 66% effective.

The second role of the vaccine in protecting you is how well it prevents you from getting seriously ill or dying if you do get COVID-19.  The COVID-19 vaccines currently approved or authorized by FDA are effective in preventing serious outcomes of COVID-19, including severe disease, hospitalization, and death.  mRNA vaccines (Pfizer-BioNTech or Moderna) have higher effectiveness compared with the Johnson & Johnson vaccine. Effectiveness against the Omicron variant is under study.  

Q. How well do these vaccines protect against variants of COVID-19?

A. The Delta variant is currently the main variant in the United States. However, the Omicron variant is spreading. Delta is more contagious and may cause more serious illness than other COVID-19 variants. Not enough is yet known about Omicron, but it appears to spread more easily than the original COVID virus. It is not yet known if Omicron causes more serious illness.
Research suggests that the vaccines may be less effective in protecting infection due to the current variants than earlier variants.  All three vaccines provide effective protection against serious illness and death from COVID-19 caused by the Delta variant. Unvaccinated people are at the greatest risk of contracting variants and becoming seriously ill. Getting vaccinated. including a booster shot, is the best step people can take to protect themselves from the variants.

Q. How available is the vaccine, and when can I get mine?

A. Everyone 12 years of age and older is now eligible to get a COVID-19 vaccination.  Get a COVID-19 vaccine as soon as you can. Get a booster as soon as you can if you have not already.

If you need help or more information, contact your state health department to find specific information on how to get vaccinated in your state.

Q. Where can I get vaccinated?

A. The federal government has created a website and other resources to assist people in finding a COVID-19 vaccination. searches for vaccination providers (such as pharmacies or healthcare professionals) in your local area. It also allows you to search by vaccine manufacturer to see which ones are offered by pharmacies in your area.  You can also text your zip code to 438829 or call 1-800-232-0233 to find COVID-19 vaccine locations (help is available in Spanish and other languages). You can also contact your own healthcare provider to make a vaccination appointment in the office.

If you or someone you care with has difficulty accessing a vaccination site, in-home vaccinations may be available. Medicare recipients can call 800-633-4227 (TTY 1-877-486-2048). The Disability Information and Access Line (DIAL) hotline is also available at 1-888-677-1199.

Q. How much will the vaccine cost?

A. The vaccine is available free of charge. Any FDA-authorized vaccine is covered under Medicare at no cost to you. People with Medicaid and private health insurance will also receive the vaccine at no cost during this public health emergency.

BE AWARE: you may receive a phone call, text, or email promising access to the vaccine in exchange for payment. These communications are scams. Do not share personal or financial information with anyone you do not know. You cannot pay to put your name on a list to get the vaccine or get early access to the vaccine.


Vaccine Function

Q. What are the risks and benefits of the vaccine?

A. We encourage everyone to discuss any concerns regarding risks and benefits of receiving a vaccination with your primary healthcare provider. Please also see the FDA fact sheets for information specific to each available vaccine: Pfizer-BioNTech, Moderna, and Johnson and Johnson.

Q. How does the vaccine work?

A. The approved vaccines train 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 a sign that the body is building protection against the virus that causes COVID-19.

It typically takes a few weeks after vaccination for the body to build immunity (protection against the virus that causes COVID-19). That means it’s possible that 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. Learn more about how COVID-19 vaccines work.

Q. I have heard that there are variants of the COVID-19 virus, such as Delta and Omicron. Will the vaccine protect me against variants?

Variants are caused when the COVID-19 virus changes (known as mutation). Different variants may spread more easily, may cause more serious disease, and may not respond as well to treatment.

Currently, the COVID-19 vaccines protect against the known variants. Vaccination is still the best protection available. However, no vaccine provides 100% protection against COVID-19 and its variants. Therefore, even people who are vaccinated should keep following recommended steps to protect themselves and others.

Q. Can getting vaccinated infect me with COVID-19?

A. 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. 

Q. Will getting a COVID-19 vaccination help prevent me from getting seriously ill with the virus?

A. Yes!  The Pfizer-BioNTech, Moderna, and Johnson & Johnson vaccines are all highly effective against getting severe illness from COVID-19.

And, if you’re around people who are at increased risk for becoming seriously ill from COVID-19, getting yourself vaccinated may help protect them as well.

After Receiving the Vaccine

Q. What’s this “herd immunity” I keep hearing about? Does it mean I don’t need the shot?

A. No, it doesn’t. “Herd immunity” means a group of people are protected against an infectious disease because the people have all become immune to it. Either they have gotten vaccinated, or they’ve developed immunity through already having the disease. Our public health experts support achieving herd immunity through vaccination, which reduces unnecessary infections and deaths.

It’s true that if you get COVID-19 and recover, you may become immune to getting the virus again. But CDC experts say that we don’t know how long this immunity might last. What’s more, your risk for becoming severely ill with COVID-19—or dying—is far riskier than any benefits of so-called “herd immunity.” When you are vaccinated against COVID-19, you experience the benefits of immunity without getting sick.

Q. I am a member of an underserved community. What COVID-19 resources are available to me?

A. As mentioned above, if you are a Medicaid recipient, you will not have to pay to receive the vaccine. Additionally, CMS’ Office of Minority Health has a set of tip sheets for vulnerable populations, including rural residents, racial and ethnic minorities, and people with disabilities.

Q. So, once I get the vaccine, can I stop wearing a mask and end social distancing?

A. Although the vaccine and the booster provide protection against catching COVID-19, many people are still not vaccinated, and the COVID-19 virus can still spread. It is still very important that we continue to use all the tools available to us to help stop this pandemic, including wearing a mask over your nose and mouth in public, washing your hands often, and staying at least 6 feet away from others in public. Getting the COVID-19 vaccination and following the CDC’s recommendations for how to protect yourself and others from getting sick will offer you the best possible protection from getting and spreading COVID-19. 


Last Updated December 2021