Home / News / A dose of facts: Answering your questions about the COVID-19 vaccines

A dose of facts: Answering your questions about the COVID-19 vaccines

Pete Zrioka

With two COVID-19 vaccines authorized for emergency use in the United States and more in development, vaccination efforts are well underway worldwide. 

The speed with which Moderna and Pfizer-BioNTech developed their vaccines, coupled with the internet’s ability to spread rumors more quickly than the coronavirus itself, means many people have questions about how the vaccines work and how safe and effective they are.

We asked experts from Arizona State University to answer some common questions about the vaccines and inoculate us against misinformation, so people can get their shots with confidence.

How does the COVID-19 vaccine work?

Both the Pfizer-BioNTech and Moderna COVID-19 vaccines are administered by injection in the upper arm. The vaccines require two doses, taken three to four weeks apart, to be fully effective.

These injections carry a little piece of the virus’s genetic code, called messenger RNA, or mRNA. mRNA contains instructions for our bodies to make a harmless piece of the virus, its spike protein. Your body identifies the spike protein as an intruder, marshaling the immune system to defend itself by creating antibodies. After creating the spike protein, your body destroys the mRNA instructions, but the antibodies remain. If you’re exposed to the coronavirus in the future, your body will recognize the spike protein and deploy antibodies in defense.

Will the COVID-19 vaccine have side effects?

Possibly. Reported side effects of the COVID-19 vaccines may include fever, chills, fatigue, headache, and pain and swelling where you received the injection. But those side effects aren’t cause for concern.

“That's a great sign. Symptoms show that your body is creating an immune response to COVID,” said Heather Ross, a clinical assistant professor in ASU’s Edson College of Nursing and Health Innovation and School for the Future of Innovation in Society. She also participated in the Moderna vaccine clinical trial over the summer.

“After the first dose, my arm was pretty sore and I had a headache, but not anything serious. After my second dose, about eight hours after the shot I had a fever, I felt super tired and pretty grumpy for about 30 hours. And then I was fine.”

These symptoms are normal signs that your body is building protection against the virus and are an expected response to a vaccine.

“The whole point is to activate your immune system,” said Anna Muldoon, who holds a master’s degree in public health and is a PhD student in the School for the Future of Innovation and Society. She currently studies the relationship between infectious disease outbreaks and social crisis in the United States. “And that means while you may feel like something activated your immune system, it doesn’t mean that something is wrong.”

While the expected side effects might be unpleasant, Ross says they pale in comparison to becoming sick with COVID-19.

“I do tell people, vaccination symptoms are a hell of a lot better than getting sick with COVID,” she said. “I have students, healthy young people, who are still getting short of breath when they try to exert themselves, months after recovering. It can be really, really disabling. We’ve seen people getting strokes after the fact from having COVID. It's really scary stuff.”

A very small number of people have had allergic reactions to the vaccine. The Centers for Disease Control and Prevention website has guidance and details on the safeguards in place. Any allergic reactions that have happened have been immediate, which is why staff members keep you at the vaccination site for about 15 minutes after you receive it to monitor for any reaction. Seasonal allergies have not been named a concern with the vaccine.

Who was the vaccine studied on?

People age 16 and older were included in the Pfizer-BioNTech study, while people 18 and up were included in the Moderna study. Combined, the clinical trials of the two vaccines included more than 70,000 people after preliminary, small-scale trials to ensure safety. Both studies included people from a variety of racial and ethnic backgrounds.

“A lot of times older adults are excluded from clinical trials, but they were definitely included here due to their vulnerability to COVID-19,” Ross said. “It was vital that these vaccines were effective for older adults.”

“If you look at the ethnic makeup of both of the vaccine trial groups, they pretty closely mirror the ethnic makeup of the United States,” said Bertram Jacobs, a professor of virology with the School of Life Sciences and a researcher in the Biodesign Institute's Center for Immunotherapy, Vaccines and Virotherapy. “And that's actually pretty unique, because for many reasons, we've had difficulty enrolling minority communities in clinical trials.”

If people close to me get vaccinated, why do I need to get a vaccine?

Getting vaccinated helps us reach herd immunity, which means most of a population is immune to a disease — either through vaccination or previous infection. It provides indirect protection to those who aren’t immune. The percentage of immune people in a population needed to reach herd immunity varies for different diseases and is unknown for COVID-19. 

“It's very possible that there might be someone in your life who can't get vaccinated, due to a suppressed immune system,” Muldoon said. “So, the more people get vaccinated, the more we can protect those people in our friend groups and families.”

Is natural herd immunity better than herd immunity by vaccination?

“Natural herd immunity” is a theoretical case of herd immunity achieved through naturally occurring infections rather than vaccines. But it may not even be possible.

“In recorded medicine, we have never reached herd immunity naturally. We have only achieved it via vaccination,” said Dr. Joshua LaBaer, executive director of ASU’s Biodesign Institute.

It would also be particularly difficult to achieve with COVID-19, because it’s unclear how long natural immunity against COVID-19 lasts after recovering from an infection.

“In this case, it's really good to have a vaccine in case natural immunity starts fading out,” Muldoon said. 

Furthermore, herd immunity through vaccination will place less strain on our health care system and will ultimately save lives. 

“Getting to ‘natural herd immunity’ means a whole lot of people are going to get sick and some are going to die,” Ross said. “And when we look at other diseases such as smallpox or polio, we would have never reached herd immunity without vaccination. What we would get is people with lifelong disabilities or who would die.”

Video by Ken Fagan/ASU

Was the COVID-19 vaccine rushed?

Yes, but that’s not a bad thing!

“It was faster than almost any other vaccine or treatment for anything in history,” Ross said. “And why was that possible? One of those reasons is that it was extremely well funded, which meant that the brain power and the work of so many people was devoted to working on these vaccines.”

Another reason the vaccines were developed so quickly is their underlying technology. Both are mRNA vaccines, which have been studied and worked on for decades. mRNA vaccines can be made using readily available materials in laboratories. This means their production can be easily standardized and scaled, hastening development.

The widespread nature of COVID-19 also allowed scientists to quickly test and develop their vaccines. To test the efficacy of a vaccine, it needs to be given to some people and not given to others. Those two groups are then followed to see who gets sick and who doesn’t.

“Normally you might have to wait years and years for enough people in a clinical trial to get exposed to an illness, but because COVID-19 is so prevalent, particularly in the United States, we had many people getting sick with it,” Ross said. “We were able to reach those study goals much faster because so many people in the clinical trials did ultimately get exposed and get sick.”

Should people who have had COVID-19 get the vaccine?

Yes. The CDC recommends that everyone be offered the vaccine, regardless of whether they have been infected. 

“We think you have some sort of immunity if you were infected,” Ross said. “But we don't know how strong it is and we also don't know how long it lasts. So yes, we are recommending that even if you had COVID-19, you should still get vaccinated.”

As more is discovered about the virus, the CDC will likely continue to update its guidance on who should receive the vaccine and when.

What do we know about the long-term effects of the COVID-19 vaccine? 

No long-term side effects have been reported for either the Moderna or Pfizer-BioNTech vaccines.

“The longest-term effects that we have are from the first people getting the vaccine back in the spring in the earliest phases of the clinical trials,” Ross said. “Those people have been followed forward and we have not seen any serious long-term effects. If there were serious long-term effects that came up, then all of that information would have been entered into the FDA process and it would not have been authorized for use.”

“The overwhelming majority of vaccine side effects show up within two months,” Muldoon said. “People don't get weird effects from a vaccine 10 years later. The body doesn't work like that.”

The Moderna and Pfizer-BioNTech vaccines contain only a few ingredients, which do not remain in the body long.

“We only have short-term data,” added Jacobs. “But I don't worry so much about long-term negative consequences, because we know they are really nonexistent in vaccines. And there's no reason to believe that this vaccine is going to be different from any others.”

What is in the COVID-19 vaccine?

The Pfizer-BioNTech and Moderna vaccines contain mRNA, lipids and saline solutions. The single active ingredient — mRNA — is contained within a protective bubble of lipids. The saline solutions in the two vaccines are commonly used in medications and vaccines and serve to keep the pH and salt levels of the mixture close to those in the human body. Both vaccines are essentially genetic material wrapped in a bubble of fat suspended in salt water.

The full ingredients of the Moderna COVID-19 vaccine are: messenger ribonucleic acid (mRNA), four lipids: SM-102; polyethylene glycol (PEG) 2000 dimyristoyl glycerol (DMG); cholesterol; 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC); and the saline solutions composed of tromethamine, tromethamine hydrochloride, acetic acid, sodium acetate and sucrose.

The full ingredients of the Pfizer-BioNTech COVID-19 vaccine are: messenger ribonucleic acid (mRNA), four lipids: (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate); 2-[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide; 1,2-Distearoyl-sn-glycero-3-phosphocholine and cholesterol; and a saline solution of potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate and sucrose.

Does the flu vaccine protect against COVID-19?

No. The flu shot does not protect against COVID-19. It protects against different strains of influenza, but influenza is a different virus than SARS-CoV-2, which causes COVID-19. 

Does the COVID-19 vaccine prevent people from getting the virus?

The Pfizer-BioNTech and Moderna vaccines are 95% and 94.1% effective. This means that almost everyone who gets vaccinated — over 94% — will be protected from getting symptomatic COVID-19 illness.

“That's very high and totally reasonable for the kinds of vaccines that we licensed in the United States regularly,” Muldoon said. “But there is no such thing as a 100% guarantee.”

The small number of people who do get infected are likely to have a milder case than they would have without the vaccine. 

“You may still get COVID-19 even after the vaccine, but it will protect you from having a serious case,” Ross added. “Because the clinical trials were designed to look for symptomatic illness, you could still get the virus, but have no symptoms and not know at all. We just don't know that yet, because that's not what the clinical trials were designed to measure.” 

For this reason, people should continue to wear masks and social distance even after vaccination.

Does the COVID-19 vaccine change your DNA?

“No, absolutely not,” Jacobs said.

While the vaccines contain genetic material (mRNA), they have no effect on our DNA. These mRNA vaccines simply deliver instructions to our cells to make a single protein from the coronavirus. Once the protein is created, those instructions are broken down and the protein piece is displayed on the surface of a cell. Our immune systems recognize that it doesn’t belong and make antibodies in defense. This is the same way our bodies respond to a natural infection.

“DNA is like a very big blueprint, let’s say 20,000 pages long. If you want to make something on page 1,000, you don’t take the whole blueprint to a factory. Instead, you make a photocopy of that page,” Jacobs said. “Then, once the factory starts making what’s on the photocopy, it’s torn up so they can start making whatever else needs to be made.”

That’s messenger RNA, Jacobs said. The mRNA does not remain in the body. It’s disposed of once it delivers its instructions and does not impact our DNA. 

Will the COVID-19 vaccines protect me from new strains of the virus? 

It’s unknown if the COVID-19 vaccines will protect from new strains of SARS-CoV-2. Preliminary research suggests that the Pfizer-BioNTech vaccine will provide protection against the more infectious strain first detected in the United Kingdom. 

Pfizer-BioNTech and Moderna vaccines prompt the body to create antibodies tailored to a region of the viral protein, and new strains of the coronavirus are exhibiting changes to that region.

“We don't think those are going to be enough changes to prevent the vaccine from working,” Jacobs said. “What we might see, though, is instead of being 95% effective, maybe the vaccines are 80% effective or 70% effective against the new strains.”

While diminished efficacy is a concern, Jacobs says both the Pfizer-BioNTech and Moderna vaccines can be quickly adapted to protect against emerging strains.

An infographic explaining how mRNA vaccines work to protect you from COVID-19.

Illustrations by Shireen Dooling

About our experts

Heather Ross is a nurse practitioner and holds a doctorate of nursing practice and PhD in human and social dimensions of science and technology. She currently serves as a special adviser to Phoenix Mayor Kate Gallego.

Anna Muldoon previously worked in the Office of the Assistant Secretary for Preparedness and Response at the Department of Health and Human Services as a science policy adviser. She currently works in Biodesign’s Modeling Emerging Threats for Arizona (METAz) Workgroup and recently co-authored COVID-19 Conspiracy Theories: QAnon, 5G, the New World Order and Other Viral Ideas

Bertram Jacobs has been working with vaccines for more than 25 years and is one of the world’s foremost experts on a poxvirus called vaccinia, a cousin of the smallpox virus. He has genetically engineered the virus as a vehicle against numerous infectious agents, bioterrorism threats, cancer and other viruses, including HIV. 

In addition to leading the Biodesign Institute, Joshua LaBaer is director of the Biodesign Virginia G. Piper Center for Personalized Diagnostics. He is an expert on using biomarkers — unique molecular signifiers of disease — as early warning signs of diseases like diabetes and cancer.