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 198 million people and more than 4 million people have died of the disease. As of September 2021, over 42 million people had been diagnosed with COVID-19 and more than 680,000 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 is in the process of applying.  All three vaccines proved in clinical trials to be highly effective at preventing people from getting sick with COVID-19 symptoms. To date, over 170 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 have 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 the Delta variant?

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 variant had not yet developed at the time the initial trials were conducted, so the Delta variant was not studied then. However, scientists have since studied the effectiveness of the vaccines against the Delta variant. All three vaccines provide highly effective protection against serious illness and death from all variants of COVID-19, including Delta.

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.

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 J&J vaccine, the CDC determined that that there is not enough data at this time to determine whether an additional dose is needed. 

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

A. According to the CDC, a booster dose 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 vaccination.

In September 2021, following FDA authorization, the CDC made recommendations for booster shots for people who have received Pfizer-BioNTech’s COVID-19 vaccine. Pfizer- BioNTech booster shots should be administered at least 6 months after receiving the second shot of the first two doses.

The CDC recommends booster shots for the following people:

  • people 65 years and older and residents in long-term care settings should receive a booster shot.
  • people aged 50–64 years with underlying medical conditions should receive a booster shot.
  • people aged 18–49 years with underlying medical conditions may receive a booster shot based on their individual benefits and risks.
  • people aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting may receive a booster shot based on their individual benefits and risks.

Pfizer- BioNTech booster shots will help increase protection against severe COVID-19 disease for these populations. If you are eligible for a booster shot, contact your healthcare professional for more information.

NOTE: The CDC has not yet released guidance on booster shots for people who have received the Moderna or Johnson & Johnson vaccines. They are currently evaluating data on the use of booster shots for the Moderna and Johnson & Johnson vaccines and will release further guidance as soon as the data are available.

The CDC also notes that while people who received the Johnson & Johnson vaccine will likely need booster shots in the future, they should NOT get shots of the Pfizer-BioNTech or Moderna vaccines.

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

A.  Which vaccine you receive will depend on which ones are available in your community. The Centers for Disease Control and Prevention (CDC) has no preference for any of the three authorized vaccines.  The most important thing is that you receive any vaccine that is available to you. Receiving any of the vaccines will provide you with protection against the most serious COVID-19 symptoms. (If you receive the Pfizer or Moderna vaccine, the second dose should be from the same manufacturer as the first dose.)

Q.  I read that the Pfizer-BioNTech vaccine has full FDA authorization, but the Moderna and Johnson & Johnson vaccines are still only authorized for emergency use. Does that mean that I should only get the Pfizer-BioNTech vaccine?

A.  All three vaccines provide protection against COVID-19. The most important thing is that you take any vaccine that is available to you.

Full FDA approval means that the Pfizer-BioNTech vaccine had an additional review process to evaluate its quality, safety, and efficacy. Pfizer-BioNTech submitted additional data and information that allowed the FDA to rule that the vaccine is safe and effective and meets the FDA’s standards for approval.

Moderna has submitted additional data that the FDA is currently evaluating and a decision is anticipated this fall.  Johnson & Johnson is in the process of applying for full FDA authorization for its vaccines. When it issued its emergency use authorization for both these vaccines, the FDA had reviewed all data from the phase 3 clinical trials and determined that both these vaccines are safe and effective.

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.

After a thorough safety review, the FDA and CDC determined that the J&J vaccine is safe and effective in preventing COVID-19, and that the vaccine’s known and potential benefits outweigh its known and potential risks.

This blood clot condition (thrombosis with thrombocytopenia syndrome) 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.

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. The Pfizer-BioNTech vaccine was found to be 95% effective at preventing COVID-19 infection, the Moderna vaccine is 94% effective, and the Johnson & Johnson vaccine is 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. All three of the vaccines have been found highly effective in preventing COVID-19–related hospitalization and death.

Q. How well do these vaccines protect against the Delta variant of COVID-19?

A. The Delta variant is more contagious and may cause more serious illness than other COVID-19 variants. Research suggests that the vaccines may be less effective in protecting infection due to the Delta variant than earlier variants.  All three vaccines provide highly effective protection against serious illness and death from COVID-19 caused by the Delta variant. Unvaccinated people are at the greatest risk of contracting the Delta variant and becoming seriously ill. Getting vaccinated is the best step people can take to protect themselves from the Delta variant.

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.

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. How much will the vaccine cost?

A. The vaccine is available free of charge. The Centers for Medicare and Medicaid Services (CMS) announced that any FDA-authorized vaccine will be 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.

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. If you do not have access to a computer, you can call 800-232-0233 for assistance (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.

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 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. The effectiveness rate of a vaccine measures how well it prevents someone from getting sick with the COVID-19 virus. The three vaccines have different rates of preventing COVID-19 infections.

However, what is most important is a vaccine's ability to prevent severe disease, especially disease severe enough to lead to hospitalization or even death. All three vaccines equally provide protection against getting severe COVID-19 disease.  

Q. I have heard that there are variants of the COVID-19 virus, such as the Delta variant. 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 and Johnson vaccines were all highly effective against getting severe 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 provides 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 September 2021