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Editor's note: This story, originally published Jan. 19, has been updated on March 2 with information about the third vaccine, Johnson & Johnson, which received emergency-use authorization on Feb. 27, as well as new guidance overall. The updated and/or new questions are clearly marked below.
With three 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, Pfizer-BioNTech and Johnson & Johnson 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.
MORE INFORMATION: ASU's COVID-19 vaccine page
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.
The SARS-CoV-2 virus is covered in a crown, or corona, of spike proteins that give coronaviruses their name. The viruses use these spike proteins to gain access to human cells.
The vaccines turn spike proteins against the virus, by teaching our bodies to recognize them as intruders and protect us from infection.
There are currently two types of COVID-19 vaccines authorized for use in the U.S. — adenovirus and messenger RNA (mRNA) vaccines. Both types of vaccines use the virus’s genetic instructions for building these spike proteins to provoke an immune response.
The Johnson & Johnson vaccine requires a single dose, administered by injection in the upper arm.
The Johnson & Johnson shot contains an adenovirus, a common virus that usually causes cold- or flu-like symptoms. This virus, however, has been reprogrammed so that it can’t replicate or make you sick. Instead, it carries DNA with instructions for the coronavirus’s spike protein.
The adenovirus is absorbed into cells where it injects its DNA into the nucleus. The cell copies the instructions for the spike protein into a messenger RNA molecule. The cell uses this mRNA like a blueprint to start building spike proteins. The spike proteins make their way to the outside of the cell, where your body recognizes them as intruders and mobilizes an immune response.
The Pfizer-BioNTech and Moderna vaccines work in a similar way, but they skip the adenovirus step. Instead of having your cells build the mRNA from DNA, they give your cells the mRNA directly. These vaccines require two doses taken 3-4 weeks apart, given by injection into the upper arm.
In both types of vaccines, the genetic instructions are destroyed after use, like a self-destructing “Mission Impossible” message. However, the antibodies created by your immune system remain. If you’re exposed to the coronavirus in the future, your body will recognize the spike protein trying to access your cells and deploy antibodies in defense.
“They are working extremely well,” says Josh LaBaer, MD, executive director of ASU’s Biodesign Institute. “The two best places to look would be in the United Kingdom and Israel, where they've had relatively successful vaccination rates among their population.”
Both nations have seen a sharp reduction in severe illness, hospitalization and death from COVID-19. This reinforces the findings of the Moderna and Pfizer-BioNTech clinical trials.
“Israel is much further along in terms of their vaccination program than we are here,” adds Megan Jehn, an infectious-disease epidemiologist and associate professor in ASU’s School of Human Evolution and Social Change. “So we have a lot of good, real-world effectiveness data showing that the vaccine seems to be performing about as we would expect it to from the clinical trial data, which is great news.”
In addition, early data suggests that the vaccines are also reducing transmission of the virus.
Research published in The Lancet examining infection rates among health care workers in the United Kingdom suggests that those who received two doses of the Pfizer-BioNTech vaccine were much less likely to become infected with the virus at all. The study reports vaccine effectiveness was 72% three weeks after the first dose and 86% seven days after the second dose, concluding that the “vaccine effectively prevents both symptomatic and asymptomatic infection in working-age adults.”
By getting vaccinated, you are not only protecting yourself from the risk of severe disease, you are also protecting the health of those around you because you’re less likely to unknowingly transmit the virus asymptomatically to friends, family members and others, says Jehn.
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. Most 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.
People age 16 and older were included in the Pfizer-BioNTech study, while people 18 and up were included in the Johnson & Johnson and Moderna studies. Combined, the clinical trials of the three vaccines included more than 110,000 people after preliminary, small-scale trials to ensure safety. All studies included men and women 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,” says Ross. “It was vital that these vaccines were effective for older adults.”
“If you look at the ethnic makeup of the Pfizer-BioNTech and Moderna vaccine trial groups, they pretty closely mirror the ethnic makeup of the United States,” says 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.”
In addition to the clinical trials, public health agencies are continuing to monitor the millions of people who have received vaccines since they were authorized, so our body of knowledge continues to grow.
Yes. While vaccine development and trials moved quickly, it was for good reason.
“This emergency situation warranted an emergency response, but that doesn't mean that there were any shortcuts that would compromise the safety of the vaccine or the scientific review process,” says Jehn. “Essentially, a number of steps that are usually done back-to-back were layered on top of one another, which is why the process was faster. For example, we started manufacturing vaccines before we knew if they would be effective, which is a big financial risk, but essential to getting vaccine out quickly.
“In order to get the emergency-use authorization, the manufacturer had to follow at least half the study participants for at least two months after completing their full vaccine series, which makes sure the vaccines are safe and effective,” Jehn adds.
Furthermore, the safety of the vaccines shown in clinical trials is being reflected in the general population.
“The rates of serious adverse effects were very low in the trials,” says LaBaer. “But more importantly, we've given this vaccine out to millions of people at this point, and we're still not seeing serious adverse events. So the number of adverse events that have been observed in all the people who are getting it today is extremely low.”
The CDC recently released a safety report examining adverse reactions to the BioNTech and Moderna vaccines from Dec. 14, 2020–Jan. 13, 2021.
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.”
“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,” LaBaer says.
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
Yes, but that’s not a bad thing!
“It was faster than almost any other vaccine or treatment for anything in history,” says Ross. “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 some of the vaccines were developed so quickly is their underlying technology. The first vaccines authorized for use, Pfizer-BioNtech and Moderna, use messenger RNA, or mRNA, which has 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 Johnson & Johnson vaccine is also based on decades of research. The company previously produced an adenovirus-based Ebola vaccine, which was approved for general use by the European Commission in July 2020.
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,” says Ross. “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.”
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,” says Ross. “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.”
Emerging data suggests that a single shot of the Pfizer-BioNTech vaccine offers strong protection to those who were previously infected. Visit the CDC vaccine FAQ page for the most updated guidance on who should receive the vaccine and when.
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.”
The Pfizer-BioNTech and Moderna vaccines contain messenger RNA (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.
The Johnson & Johnson vaccine contains a modified adenovirus with coronavirus DNA, as well as various stabilizers, alcohol for sterilization, an anticoagulant, an emulsifier to hold the ingredients together and salt.
The full ingredients of the Johnson & Johnson vaccine are: recombinant, replication-incompetent adenovirus type 26 expressing the SARS-CoV-2 spike protein, citric acid monohydrate, trisodium citrate dihydrate, ethanol, 2-hydroxypropyl-β-cyclodextrin (HBCD), polysorbate-80 and sodium chloride.
Polyethylene glycol, or PEG, is a petroleum-derived compound that’s found in everything from medicine and food to cosmetics and industrial products. PEG is in both the Pfizer-BioNTech and Moderna vaccines, where it’s used as a stabilizing agent for the mRNA.
“It’s used in the vaccines to make sure the active component doesn't fall apart, dry up, degrade or become unusable until it gets delivered to the body,” says LaBaer. “It’s used in all kinds of substances that we take all the time. Generally speaking, the vast majority of people have no problem with polyethylene glycol, but there are individuals that have allergic reactions to PEG.”
The Johnson & Johnson vaccine does not contain PEG, but it does contain polysorbate. A small number of people are allergic to polysorbate.
If you have a history of severe allergic reactions, check the CDC guidelines to see if you should receive a COVID-19 vaccine.
No. The flu shot does not protect against COVID-19. The flu is caused by influenza viruses, while COVID-19 is caused by a type of coronavirus.
The vast majority of people who get vaccinated will be protected from getting severe, COVID-19 illness, and most people will be protected from getting sick at all.
Johnson & Johnson reports their vaccine to be 66% effective in preventing moderate to severe cases of COVID-19 and 85% effective in preventing severe forms of COVID-19. The Pfizer-BioNTech and Moderna vaccines have reported efficacy of 95% and 94.1%.
“That's very high and totally reasonable for the kinds of vaccines that we licensed in the United States regularly,” says Muldoon. “But there is...