Get the latest information and guidance about the three COVID-19 vaccines authorized for emergency use, updated May 27, 2021.
Illustration by Shireen Dooling
By Pete Zrioka
Jan. 20, 2021
Updated May 27, 2021
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.
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 do the COVID-19 vaccines work? [UPDATED]
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.
Learn more about how vaccines work to protect your body from ASU's Ask A Biologist.
How are the vaccines working so far? [NEW]
“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.
Will the COVID-19 vaccines have side effects?
Possibly. Reported side effects of the COVID-19 vaccines include fever, chills, fatigue, headache, and pain and swelling where you received the injection. But those side effects are typically short-lived and not cause for concern.
“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,” she says.
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,” says 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 crises 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 says. “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.”
Does the Johnson & Johnson COVID-19 vaccine cause blood clots? [UPDATED]
There have been very rare cases of blood clots following use of the Johnson & Johnson vaccine.
Six cases of blood clots were reported out of nearly 7 million Johnson & Johnson shots administered. U.S. federal regulators paused distribution of the vaccine on April 13 in order to investigate further. The pause was lifted on April 23 after regulators determined the chance of blood clots to be very low. The six cases of blood clots were in women between the ages of 18 and 48, with symptoms appearing within three weeks of the single-dose vaccination.
“This is the kind of rare event that you can only observe when you actually deploy a therapeutic in millions of people and keep very careful records,” says LaBaer. “Under less closely scrutinized circumstances, if this had been any other therapeutic, which was not watched as closely, this kind of rare event would have taken much longer to notice.”
Though he notes all drugs carry some degree of risk, LaBaer says the health risks posed by an actual COVID-19 infection remains much greater.
“COVID-19 kills about 2% of the people that it infects, that is one in 50. One quarter of the people who died in Arizona from COVID-19 were middle-aged or younger. The re-evaluation of these blood clots are for six people noted nationwide. In the same age group, 700 people died in Arizona alone from COVID19. Moreover, many more people who did not die from COVID19 may be living for a very long time with consequences of having had COVID,” he adds.
The CDC and FDA recommends that recipients of the Johnson & Johnson vaccine contact their doctors if they develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination.
Who was the vaccine studied on? [UPDATED]
People ages 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.
ASU's Ask A Biologist explains how vaccines are tested.
Were the clinical trials large and long enough to ensure safety? [NEW]
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.”
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 still 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,” says Muldoon. “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,” says LaBaer.
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,” says Muldoon.
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,” says Ross. “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.”
Was the COVID-19 vaccine rushed? [UPDATED]
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.”
Should people who have had COVID-19 get the vaccine? [UPDATED]
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.”
The above video from ASU's Ask A Biologist focuses on who should get a COVID-19 vaccine and why.
What do we know about the long-term effects of the COVID-19 vaccine?
No long-term side effects have been reported for the COVID-19 vaccines.
“The longest-term effects that we have are from the first people getting the vaccine back in spring 2020 in the earliest phases of the clinical trials,” says Ross. “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,” says Muldoon. “People don't get weird effects from a vaccine 10 years later. The body doesn't work like that.”
“We only have short term data,” adds 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 vaccines? [UPDATED]
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 comprised 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.
What is PEG and is it in the vaccines? [NEW]
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.
Does the flu vaccine protect against COVID-19?
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.
Does the COVID-19 vaccine prevent people from getting the virus? [UPDATED]
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 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,” adds Ross. “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 who have been vaccinated should continue to wear masks and social distance around unvaccinated individuals.
Should I still get tested after I get vaccinated? [NEW]
Yes, if you have symptoms or have been exposed to someone who tested positive. Vaccination is not a golden ticket to never worry about the coronavirus again. The risk of infection is reduced, but not eliminated.
“People can still get infected, which means they can still carry the virus,” says LaBaer. “And until we get a greater proportion of our population vaccinated, testing is a way of making sure people aren't asymptomatically carrying the virus.”
“It's probably a safe thing to get tested if you have had a high-risk exposure, such as prolonged close contact with somebody who's tested positive,” says Jehn. “We do know that vaccines aren’t perfect and people may still get infected. So I do think it's reasonable to continue testing for the near term while we have high levels of circulating virus in our community.”
LaBaer, who has been vaccinated, gets tested when the situation calls for it.
“If I'm going to be near somebody who hasn't been vaccinated or I travel, or I’m heading to an in-person meeting, I'll get tested,” he says.
While Pfizer-BioNTech and Moderna vaccines contain genetic material (mRNA), they have no effect on our DNA. These messenger RNA (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,” says Jacobs. “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, says Jacobs. 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 the new strains of the virus? [UPDATED]
We don’t know if the COVID-19 vaccines will protect against 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 the virus’s spike 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,” says Jacobs. “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.
“It is worth noting that even though the vaccines have not yet been formally tested on the variants, they are still proving effective when measured in geographical areas that have high rates of variants,” adds LaBaer, pointing to the Johnson & Johnson clinical trial in South Africa.
In the trial, 92% of sequenced cases were the more infectious South African variant of the virus, though the vaccine proved effective in preventing moderate to severe COVID-19 73% of the time at 14 days and 82% at 28 days.
“My guess is that the vaccines are going to be effective for a long time,” says LaBaer. “I'm hopeful, because this is not like the flu virus, which constantly changes its look and its antigens. This virus doesn't change that fast and the vaccines seem to be pretty broadly effective.”
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 advisor to Phoenix Mayor Kate Gallego.
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.
Megan Jehn received her doctorate and master's of health science degrees from the Johns Hopkins School of Public Health in clinical epidemiology. She played an integral role in Maricopa County’s Serosurvey and is a member of the Arizona CoVHORT, a collaboration between public health and medical researchers to examine COVID-19’s effects on Arizona.
In addition to leading the Biodesign Institute, Josh 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.