COVID-19 vaccines: The tough questions answered by a frontline doctor

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The arrival of highly effective COVID-19 vaccines marks a new and hopeful phase of the pandemic. Health care workers at UT Southwestern began getting vaccinated on Dec. 15.

For the last 10 months, there has been one big question hovering over the COVID-19 vaccine conversation: “When will one be ready?”

Now that two vaccines have been authorized by the Food and Drug Administration (FDA) for emergency use, there are many more questions, such as:

  • How safe and effective are the vaccines?
  • Who will be the first in line to get one?
  • What, if any, side effects do they cause?
  • And will a vaccine finally bring an end to the pandemic?

Creating and testing multiple COVID-19 vaccines in less than a year marks a major achievement for the scientific community, and it shatters the record for the fastest vaccine ever developed (mumps; four years). But now come the very real logistical concerns about how to vaccinate millions in the midst of a pandemic – while also instilling confidence in the new treatment. In a November Gallup poll, only 58% of Americans said they would get a COVID-19 vaccine, up from 50% in September. Most experts say that vaccination rates will need to reach at least 70% to have a chance at achieving herd immunity.

UT Southwestern’s epidemiologists and infectious disease specialists are continuing to review the safety data but all evidence points to the same conclusion: These two vaccines are safe and effective.

Amidst the blizzard of conflicting information about vaccines, we know you still have questions. So here are evidence-based answers about the COVID-19 vaccines from a medical professional who will be among the first in line to take one.

The Making of a COVID-19 Vaccine

See how the complex process works and how it has been accelerated to combat the pandemic.

1. What’s in the vaccine and how does it work?

The vaccines, created by Pfizer/BioNTech and Moderna, both use what’s called messenger RNA (mRNA), which in this case is a synthetic material that carries the genetic code used to make the SARS-CoV-2 spike protein. The spike is the part of the virus that attaches to human cells. The mRNA is showing your immune system a part of the virus, so that when your body encounters the whole virus in real-life, it recognizes the invader and is able to mount a quick immune response, activating antibodies (B and T-cells) to fight it. That’s how the mRNA vaccines work.

While many vaccines use a weakened or inactive version of the virus to create an immune response, mRNA doesn’t contain any live virus, so there is no risk of it causing disease. The mRNA also never enters the nucleus of the cell and does not affect a person’s DNA. The body also contains enzymes that break down mRNA quickly, reducing chances for long-range side effects.

Vaccines using mRNA are new but the technology has been around for decades and has been used in treatments for other diseases such as cancer and cystic fibrosis. Another benefit to mRNA is that manufacturing large quantities of it is easier because scientists don’t have to grow live virus in a lab to make the vaccine. Pfizer and Moderna have said they expect to deliver between 50 million and 100 million doses of their vaccines by early 2021.

2. How effective are the vaccines?

In Phase 3 clinical trials involving thousands of people, both vaccines were nearly 95% effective in preventing COVID-19, which is about as good as it gets, according to the nation’s top infectious disease experts, including Trish Perl, M.D., Chief of UT Southwestern’s Infectious Diseases Division.

For context, the FDA had suggested a coronavirus vaccine would need to be at least 50% effective to earn emergency authorization. Most experts had hoped for 70%. The early results put COVID-19 vaccines in the efficacy realm of shots for chickenpox (92%), measles-mumps-rubella (97%); and polio (99%).

According to safety data for Pfizer’s Phase 3 trial, 44,000 people participated and half of those got the vaccine; the other half were given a placebo. A total of 170 people out of the 44,000 had symptomatic cases of COVID-19, but only eight (about 5%) were in the vaccine group. None of those eight had severe complications, which could mean that even if one gets COVID-19 after receiving the vaccine, the vaccine may prevent the most severe complications, much like the results of the influenza vaccine. Moderna’s Phase 3 trial included 30,000 participants and produced 95 cases of symptomatic COVID-19. Only five in the vaccinated group got COVID-19, none with serious complications.

UT Southwestern’s Vaccine Science Review Committee independently reviewed clinical trial data of the vaccine candidates and expressed confidence that they are safe and effective.

3. Will the vaccines protect against new strains of the virus, such as the one in the U.K.?

There is no reason to think that this mutation will impact the efficacy of the two vaccines that are currently available. Several mutations of the SARS-CoV-2 virus have been documented since the beginning of the pandemic, and this new lineage detected in the U.K. has three mutations in the spike protein, which may affect its ability to bind more effectively to host cells. The scientific community will continue to investigate the mutation, which was detected during a regional surge of cases in Southeast England, but this simply reinforces the need to get vaccinated when it becomes available to you and to continue observing safety measures to reduce the spread of COVID-19.

4. How do we know steps weren’t skipped to produce the vaccines faster?

There is a well-established testing and clinical trial regimen that must be followed for the FDA to consider approving a vaccine. For these COVID-19 vaccines, the research was performed concurrently, rather than consecutively, and the wait times for review of the research were substantially reduced through Operation Warp Speed, a federal program that invested in development and manufacturing of the vaccines.

No steps were skipped, and safety was not sacrificed for speed.

An independent and transparent monitoring board of experts reviewed the trial data, and career scientists evaluated it at the FDA. All of the clinical trial information will be published in peer-reviewed journals.

5. Why do the vaccines require two shots, and what if you miss the second shot?

The first shot triggers the immune response, and the second one, often called a “booster,” primes the body to memorize the virus so it will recognize it immediately in the future and fight it off. Many vaccines require boosters, such as tetanus, shingles, and MMR.

The COVID-19 vaccines each require a second shot (21 days apart for Pfizer; 28 for Moderna). If you skip the second shot it’s less likely you’ll develop full immunity, not to mention wasting a valuable dose of vaccine. Health care providers will try to make it as convenient as possible to set up both appointments at the same time and will provide reminders to get the second shot.

6. Do the vaccines have any serious side effects?

Some trial participants experienced arm soreness, fatigue, chills, fever, or headaches that lasted a day or two, most often after the second shot. But that reaction is typically a sign that the vaccine is working – triggering the immune response (or inflammation) indicating your body recognizes this never-before-seen pathogen and is mounting a protective response against it.

The clinical trials will continue to monitor patients for side effects long after patients are vaccinated. The state of Texas will use the Vaccine Adverse Event Reporting System (VAERS), a national system co-managed by the Centers for Disease Control (CDC) and FDA, to track vaccine safety and side effects. Texas will also employ an app called v-safe, which sends vaccine recipients text messages and check-in emails to keep tabs on their health, as well as remind them when it’s time to get their second shot.

7. Do the vaccines present any long-term health risks?

Phase 3 vaccine trial participants were monitored for 60 days after receiving their second shot, which is required before any safety data can be submitted to the FDA. Typically, if a patient hasn’t experienced severe side effects in 60 days, it is extremely unlikely they will. But because these vaccines are so new, significant long-term data are still being collected.

According to clinical trial safety documents released by the FDA on Dec. 7, there were four cases of Bell's palsy, a condition that temporarily weakens the facial muscles, among Pfizer clinical trial participants who received the vaccine. The rates of Bell’s palsy, however, were no different than what occurs in the general population and there is no evidence the vaccine caused the problem. Still, the FDA is likely to recommend follow-up investigation.

Vaccine Pfizer/BioNTech Moderna
Technology mRNA mRNA
Phase 3 trial participants 44,000 30,000
Efficacy rate 95% 94.5%
Doses needed 2, 21 days apart 2, 28 days apart
Status Authorized by FDA Authorized by FDA
Storage temperature -94 degrees Fahrenheit -4 degrees Fahrenheit

Immunity across different populations

8. How long does it take for immunity to develop after getting vaccinated?

The FDA documents said the Pfizer vaccine showed more than 50% immunity 10 days after the first shot, and 95% immunity seven days after the second shot.

The booster is necessary to strengthen the immune response and provide near full protection. Also, keep in mind that exposure is still possible between doses, so continue to wear a mask and follow hand-washing and physical distancing recommendations.

9. How long will immunity to COVID-19 last?

There’s no definitive way to tell yet, but some studies have indicated it could last years, even decades. The research showed that patients who contracted COVID-19 early in 2020 had robust antibodies six months later. Studies of survivors of SARS, also caused by a coronavirus, showed that participants carried immune cells 17 years after being infected. So there are some reasons to be encouraged, but scientists will need to continue monitoring the length and strength of immune responses in vaccinated patients.

10. Do the vaccines work in older and more vulnerable people?

The vaccines appear to maintain high efficacy rates regardless of age, sex, and ethnicity. For example, Pfizer’s vaccine was 94% effective in adults over age 65, according to safety data. Both vaccines have also been tested in people with stable pre-existing conditions such as diabetes and cancer, and efficacy rates held at essentially the same levels.

11. Will the vaccines be safe for children and pregnant women?

The clinical trials did not include children or expectant mothers, so they may have to wait as the Phase 3 and Phase 4 trials continue to expand. Pfizer, which recommends its vaccine for ages 16 and up, began vaccinating children ages 12-15 in trials in October; Moderna began enrolling ages 12-17 in early December. Results could be available in early spring.

Vaccines meant for adults and children are typically tested in adults first to ensure they’re safe before pediatric trials begin. Historically, pregnant women have not been included in vaccine trials, but there were a small number of women in the Pfizer clinical trial that became pregnant during the study, without any short-term complications. The Advisory Committee on Immunization Practices has said it will issue guidance soon on when or if pregnant patients should get vaccinated.

12. Will the vaccine affect fertility in women?

There is no evidence or reason to think COVID-19 vaccines affect fertility, despite some claims to the contrary circulating on the internet. Those reports are rooted in the theory that because the SARS-CoV-2 spike protein resembles the syncytin-1 protein, which is crucial for formation of the placenta, the COVID-19 vaccines might prompt an immune response that targets the placenta protein. But virologists say the two proteins are completely unrelated and not similar enough to confuse antibodies that attack the virus.

13. Do people who have recovered from COVID-19 need to get vaccinated?

It’s unclear how long natural immunity lasts after recovering from COVID-19, and there has been some data to suggest it begins to wane after 90 days. Similarly, the level of immunity you have after COVID-19 therapies such as convalescent plasma or monoclonal antibodies is unknown. There have been a few reported cases of re-infection, so the CDC may advise people to get a vaccine even if they have been sick with COVID-19 before.

Vaccine distribution and logistics

14. Who will get the vaccine first and how is that decided?

The CDC’s Advisory Committee on Immunization Practices (ACIP) on Dec. 1 recommended that the first recipients of the vaccine should be health care workers who are most at risk of exposure to COVID-19 (about 21 million people nationwide) and residents of long-term care facilities (2 million), a group that accounts for 40% of U.S. deaths from COVID-19. Those groups, including UT Southwestern frontline workers, began receiving vaccinations in mid-December.

On Dec. 21, the Texas Department of State Health Services announced that Texans who are 65 years old and older, and those who are at least 16 with certain chronic medical conditions will be next in line for the COVID-19 vaccine. The medical conditions include but are not limited to: cancer; chronic kidney disease; chronic obstructive pulmonary disease; heart conditions; solid organ transplantation; obesity and severe obesity; pregnancy; sickle cell disease; and type 2 diabetes mellitus.

On Jan. 4, 2021, UT Southwestern began offering vaccination appointments to its eligible patients. Please visit our Vaccination Page for more details.

For updates on vaccine distribution in Texas, you can check the

15. When is the vaccine likely to be available to everyone?

When the vaccines will be available to the general public depends on many factors, including manufacturing, delivery, and distribution. Every effort will be made to distribute the vaccine equitably and as quickly as possible, but some vaccines must be transported and stored at very low temperatures, which could limit availability. For updates on UT Southwestern's vaccination efforts, please the visit the Vaccination Page on our website.

16. Why do some vaccines need to be stored in such cold temperatures?

Cold chain requirements vary and are based on the formulation of the vaccine. In some, such as the Pfizer vaccine (stored at -94 degrees Fahrenheit; think dry ice), the molecules become unstable and degrade if they are left out in warmer temperatures. Moderna’s vaccine needs to be stored at -4 degrees Fahrenheit, or about the temperature of a regular freezer.

With more study, it could become apparent that the vaccines don’t require such low temperatures, but they were developed and tested in a specific way during the clinical trials so that is the protocol to follow. Several other vaccines in development, such as one from Johnson & Johnson, require only refrigeration.

17. Will we have enough of the vaccine?

Supplies will be limited at first, which is why state and federal officials have created a phased release schedule. Operation Warp Speed pre-purchased hundreds of millions of doses from six manufacturers, all of whom have been producing vaccine even while seeking FDA approval.

Pfizer says it plans to produce 1.3 billion doses by the end of 2021. Moderna’s totals range between 500 million and 1 billion doses. But the question of whether we’ll have enough will also be determined, to a large extent, by how many people choose to get the vaccine.

18. Where will the vaccine be available?

At first, hospitals and health care facilities will be the primary places to receive a vaccine. Some states are planning to set up immunization sites in the community. Eventually, you’ll be able to get them at your doctor’s office or at retail pharmacies. Drive-up facilities, which have become commonplace for COVID-19 tests, are unlikely to be used for vaccines, at least at first, because it’s standard practice to observe a patient for a short period of time following the shot.

19. How much will a vaccine cost?

Vaccines have already been paid for by the federal government with taxpayers’ money, so officials have said repeatedly they will be free. Vaccine providers may charge an administration fee, but it would likely be covered by health insurance.

Life after getting vaccinated

20. If I get the vaccine, does that mean I can’t transmit the disease?

Both vaccines are very effective, according to safety data, but they’re not 100% effective. So it is still possible, but highly unlikely, that you could contract COVID-19 and also spread it.

Also, the vaccine trials tested whether participants would produce antibodies to shield them from developing COVID-19 symptoms or severe illness. It’s still not clear if vaccinated people could develop asymptomatic infection and potentially spread the virus.

21. Will I still need to wear a mask and social distance after getting vaccinated?

Yes. People will be getting vaccinated throughout December and much of 2021. Until a majority of the population has been vaccinated – some estimates say vaccinating 70% of Americans would help us reach herd immunity – wearing a mask, washing your hands, practicing physical distancing, and avoiding large, indoor gatherings will continue to be important tools to limit spread.

22. Do the benefits of getting the vaccine outweigh the risks?

Ultimately, this is the question you should ask yourself if you are unsure about whether to get vaccinated. But after evaluating the trial data and considering the documented record of vaccines in general, the answer is unequivocal: Yes, the benefits outweigh the risks.

Vaccinology is one of the safest interventions we have in patient care and disease prevention, and it has a long history of protecting the public – from smallpox to polio to measles. Yes, there are low-grade side effects, but they seem minor compared to the protections and freedom that safe and effective COVID-19 vaccines can provide.

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