top of page

UC Davis

How COVID-19 vaccines work: Answers for you (

The real facts about common COVID-19 vaccine myths (

John Hopkins Medical Clinic

COVID-19 Vaccines: Myth Versus Fact | Johns Hopkins Medicine

Is the COVID-19 Vaccine Safe? | Johns Hopkins Medicine

Mayo Clinic

Coronavirus disease 2019 (COVID-19) from Mayo Clinic - Mayo Clinic

COVID-19 vaccine myths debunked – Mayo Clinic News Network

National Institutes of Health

COVID-19 Vaccines | NIH COVID-19 Research


John Hopkins

MYTH: The COVID-19 vaccine can affect women’s fertility.

FACT: The COVID-19 vaccine will not affect fertility.


The truth is that the COVID-19 vaccine encourages the body to create copies of the spike protein found on the coronavirus’s surface. This “teaches” the body’s immune system to fight the virus that has that specific spike protein on it.

Confusion arose when a false report surfaced on social media, saying that the spike protein on this coronavirus was the same as another spike protein called syncitin-1 that is involved in the growth and attachment of the placenta during pregnancy. The false report said that getting the COVID-19 vaccine would cause a woman’s body to fight this different spike protein and affect her fertility. The two spike proteins are completely different and distinct, and getting the COVID-19 vaccine will not affect the fertility of women who are seeking to become pregnant, including through in vitro fertilization methods. During the Pfizer vaccine tests, 23 women volunteers involved in the study became pregnant, and the only one who suffered a pregnancy loss had not received the actual vaccine, but a placebo. Getting COVID-19, on the other hand, can have potentially serious impact on pregnancy and the mother’s health. Learn more about coronavirus and pregnancy. Johns Hopkins Medicine encourages women to reach out to their medical providers to discuss other questions they have about COVID-19 as it relates to fertility or pregnancy.


Fact: The vaccines do not cause infertility.

“There is no evidence at all that they have any effect on fertility,” Blumberg said.


The 50-plus page briefings from the Vaccines and Related Biological Products Advisory Committee


(VRBPAC) for both Pfizer and Moderna to the full FDA detail all the findings from the clinical trials about effectiveness, safety and side effects. There are no reports of any impact on fertility.

Mayo Clinic

Key takeaways


If you are pregnant or breastfeeding, it’s recommended that you get a COVID-19 vaccine. Getting a COVID-19 vaccine can protect you from severe illness due to COVID-19. Vaccination can also help pregnant women build antibodies that might protect their babies.


COVID-19 vaccines don’t cause infection with the COVID-19 virus, including in pregnant women or their babies. None of the COVID-19 vaccines contain the live virus that causes COVID-19.


While further research is needed, early findings suggests that getting an mRNA COVID-19 vaccine during pregnancy poses no serious risks for pregnant women who were vaccinated or their babies.


Keep in mind that the mRNA COVID-19 vaccines don’t alter your DNA or cause genetic changes. In addition, vaccines that use the same viral vector as the Janssen/Johnson & Johnson COVID-19 vaccine have been given to pregnant women in each trimester of pregnancy in clinical trials. No harmful effects were found.


If you have concerns, talk to your doctor about the risks and benefits.

John Hopkins

MYTH: If I’ve already had COVID-19, I don’t need a vaccine.

FACT: Evidence continues to indicate that getting a COVID-19 vaccine is the best protection against getting COVID-19, whether you have already had COVID-19 or not.

  • study published in August 2021 indicates that if you had COVID-19 before and are not vaccinated, your risk of getting reinfected is more than two times higher than for those who were infected and got vaccinated.

  • While evidence suggests there is some level of immunity for those who previously had COVID, it is not known how long you are protected from getting COVID-19 again. Plus, the level of immunity provided by the vaccines after having COVID-19 is higher than the level of immunity for those who had COVID but were not subsequently vaccinated.

  • Getting vaccinated provides greater protection to others since the vaccine helps reduce the spread of COVID-19.

At the time of vaccination, be sure to tell your care provider about your history of COVID-19 illness, including the kind of treatment, if any, you received and when you recovered. Wait until your isolation period ends before making an appointment to get the vaccination.

Mayo Clinic

Key takeaways

Getting COVID-19 might offer some natural protection or immunity from reinfection with the COVID-19 virus. But it’s not clear how long this protection lasts.

Because it’s possible to get reinfected and COVID-19 can cause severe medical complications, the Centers for Disease Control and Prevention recommends that people who have already had COVID-19 get a COVID-19 vaccine.

If you were treated for COVID-19 with monoclonal antibodies or convalescent plasma, wait 90 days before getting a COVID-19 vaccine.

John Hopkins

MYTH: Researchers rushed the development of the COVID-19 vaccine, so its effectiveness and safety cannot be trusted.

FACT: Studies found that the two initial vaccines are both about 95% effective — and reported no serious or life-threatening side effects. There are many reasons why the COVID-19 vaccines could be developed so quickly. Here are just a few:

  • The COVID-19 vaccines from Pfizer/BioNTech and Moderna were created with a method that has been in development for years, so the companies could start the vaccine development process early in the pandemic.

  • China isolated and shared genetic information about COVID-19 promptly, so scientists could start working on vaccines.

  • The vaccine developers didn’t skip any testing steps, but conducted some of the steps on an overlapping schedule to gather data faster.

  • Vaccine projects had plenty of resources, as governments invested in research and/or paid for vaccines in advance.

  • Some types of COVID-19 vaccines were created using messenger RNA (mRNA), which allows a faster approach than the traditional way that vaccines are made.

  • Social media helped companies find and engage study volunteers, and many were willing to help with COVID-19 vaccine research.

  • Because COVID-19 is so contagious and widespread, it did not take long to see if the vaccine worked for the study volunteers who were vaccinated.

  • Companies began making vaccines early in the process — even before FDA authorization — so some supplies were ready when authorization occurred.

UC Davis

Fact: The vaccines are safe and went through full reviews by experts.

“The vaccines have been very well studied,” Blumberg said. “There were 43,661 people enrolled in the randomized Pfizer clinical trial, including 225 at UC Davis Health, which was one of 150 sites to take part the trial. The results were carefully reviewed. Both vaccines have been scientifically proven to be very safe.” 

The U.S Food & Drug Administration (FDA) and other experts reviewed the data from Covid-19 vaccine trials more quickly than usual by looking at data as information came in. In most cases, they wait until the trials are complete. They used the same demanding safety and efficacy standards as always and no safety protocols were changed or skipped. 

“No safeguards were sacrificed,” he said. 

Fact: The vaccines were developed quickly because of the worldwide effort.

 “The vaccines were made at record speed,” Blumberg said. “Vaccines often take 7-10 years.” 

The COVID-19 vaccines went through careful clinical trials and a full safety review. The evidence clearly shows they are effective and safe.

Along with the constant review by regulatory experts that sped up the process, there were two other reasons for the speed. The first was our urgency. Vaccine manufacturers and the scientific community dropped everything to develop a vaccine. 

“We’ve never seen anything like this before,” Blumberg said. “There was a huge effort from universities, public health experts, manufacturers, epidemiologists and many others. If you spend unlimited time and money, you can overcome a lot of problems really fast.” 

The second was that the innovative mRNA approach was already in development. Researchers had already created the way of getting the mRNA into the body – what’s called an mRNA platform – for trials on cancer efforts and other vaccines. What they needed to learn was the genomic sequence of the coronavirus. 

“The vaccine platforms were developed just in case there was a pandemic,” Blumberg said. “Much of the research was to figure out what to put into the COVID-19 vaccines.” 

Mayo Clinic

Data must show that a COVID-19 vaccine is safe and effective before the Food and Drug Administration (FDA) can give emergency use authorization or approval. The safety of COVID-19 vaccines is closely monitored by the Centers for Disease Control and Prevention (CDC) and FDA.

The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 16 and older. The FDA approved Comirnaty after data found the vaccine is safe and effective.

Vaccines with emergency use authorization by the FDA include:

  • Pfizer-BioNTech COVID-19 vaccine for children ages 12 to 15

  • Moderna COVID-19 vaccine

  • Janssen/Johnson & Johnson COVID-19 vaccine

John Hopkins

MYTH: Getting the COVID-19 vaccine means I can stop wearing my mask and taking coronavirus precautions.

FACT: The CDC continues to monitor the spread of COVID-19 and makes recommendations for wearing face masks, both for those who are fully vaccinated as well as those who are not fully vaccinated.

The CDC also recommends that masks and physical distancing are required when going to the doctor’s office, hospitals or long-term care facilities, including all Johns Hopkins hospitals, care centers and offices.

Johns Hopkins Medicine’s current mask safety guidelines have not changed, and we still require all individuals to wear masks inside all of our facilities.

Mayo Clinic

Key takeaways

After you’re fully vaccinated, you can more safely return to doing activities that you might not have been able to do because of the pandemic. You can also stop wearing a mask or social distancing in any setting, except where required by a rule or law. However, if you are in an area with a high number of new COVID-19 cases in the last week, the CDC recommends wearing a mask indoors in public and outdoors in crowded areas or when you are in close contact with unvaccinated people. If you are fully vaccinated and have a condition or are taking medications that weaken your immune system, you may need to keep wearing a mask. You’re considered fully vaccinated two weeks after you get your second dose of a messenger RNA (mRNA) vaccine, such as Pfizer-BioNTech or Moderna, or two weeks after a single dose of the Janssen/Johnson & Johnson vaccine.

John Hopkins

MYTH: Getting the COVID-19 vaccine gives you COVID-19.

FACT: The vaccine for COVID-19 cannot and will not give you COVID-19.

The two authorized mRNA vaccines instruct your cells to reproduce a protein that is part of the SARS-CoV-2 coronavirus, which helps your body recognize and fight the virus, if it comes along. The COVID-19 vaccine does not contain the SARS-Co-2 virus, so you cannot get COVID-19 from the vaccine. The protein that helps your immune system recognize and fight the virus does not cause infection of any sort.


Fact: The vaccines will not give you COVID-19.

“There is absolutely no way you can get COVID-19 from the vaccine. It is not possible,” said Blumberg. “None of the vaccines being developed use the live virus. There is nothing in the vaccine that could cause COVID-19.” 

The Pfizer and Moderna vaccines use mRNA, which stands for messenger ribonucleic acid. In simple terms, mRNA carries instructions to your body about how to build a protein. In this case, it’s telling your body to make the spike protein that’s on the coronavirus. 

“The vaccines have been scientifically proven to be very safe ... No safeguards were sacrificed.”

— Dean Blumberg

The proteins your body makes are solitary, and they do not connect or reproduce. Then your immune system recognizes the protein as foreign and develops antibodies to destroy it. Your immune system remembers the protein and is ready to attack and eliminate the real SARS-CoV-2 virus. 

“Our own cells make the protein and it can’t replicate,” Blumberg said. “The mRNA doesn’t stay around long. Your body breaks it down and gets rid of it. The vaccines teach your body to fight the virus so your immune response will protect you.” 


John Hopkins

MYTH: The side effects of the COVID-19 vaccine are dangerous.

FACT: In April 2021, the CDC temporarily paused and then resumed use of the Johnson & Johnson vaccine. 

Read full story.

The Pfizer and Moderna COVID-19 vaccines can have side effects, but the vast majority are very short term —not serious or dangerous. The vaccine developers report that some people experience pain where they were injected; body aches; headaches or fever, lasting for a day or two. These are signs that the vaccine is working to stimulate your immune system. If symptoms persist beyond two days, you should call your doctor.

If you have allergies — especially severe ones that require you to carry an EpiPen — discuss the COVID-19 vaccine with your doctor, who can assess your risk and provide more information about if and how you can get vaccinated safely.


Could I get COVID-19 from the vaccine?

“There is absolutely no way you can get COVID-19 from the vaccine. It is not possible,” said Blumberg. “None of the vaccines currently authorized in the U.S. use the live virus. There is nothing in the vaccine that could cause COVID-19.”


Vaccine side-effects

How COVID-19 vaccine works, potential side effects | Coronavirus | UC Davis Health


Mayo Clinic

Key takeaways


COVID-19 vaccines can cause mild side effects after the first or second dose, including:

  • Pain, redness or swelling where the shot was given

  • Fever

  • Fatigue

  • Headache

  • Muscle pain

  • Chills

  • Joint pain

  • Nausea and vomiting

  • Swollen lymph nodes

Most side effects happen within the first three days after vaccination and typically last only 1 to 2 days.

In the U.S., there has been an increase in reported cases of myocarditis and pericarditis after mRNA COVID-19 vaccination, particularly in male adolescents and young adults age 16 and older. Myocarditis is the inflammation of the heart muscle, while pericarditis is the inflammation of the lining outside the heart. These reports are rare. The CDC is investigating to see if there is any relationship to COVID-19 vaccination.

Serious side effects of the Janssen/Johnson & Johnson COVID-19 vaccine can occur within three weeks of vaccination and require emergency care. Possible symptoms include:

  • Shortness of breath

  • Persistent stomach pain

  • Severe or persistent headaches or blurred vision

  • Chest pain

  • Leg swelling

  • Easy bruising or tiny red spots on the skin beyond the injection site

Mild to moderate headaches and muscle aches are common in the first three days after vaccination and don’t require emergency care.

Rarely, some people may develop Guillain-Barre syndrome after getting the Janssen/Johnson & Johnson COVID-19 vaccine. Seek immediate medical care if you have weakness or tingling sensations, difficulty walking, difficulty with facial movements, double vision, and difficulty with bladder control.

John Hopkins

MYTH: The COVID-19 vaccine enters your cells and changes your DNA.

FACT: The COVID-19 vaccines are designed to help your body’s immune system fight the coronavirus.


The messenger RNA from two of the first types of COVID-19 vaccines does enter cells, but not the nucleus of the cells where DNA resides. The mRNA does its job to cause the cell to make protein to stimulate the immune system, and then it quickly breaks down — without affecting your DNA.


Fact: The vaccines will not change your DNA. 

There is nothing in either vaccine that could affect anyone’s genetic makeup.

“There is no DNA of any kind in either vaccine. The vaccines don’t change us in any way, except to help us build immunity to COVID-19.”

— Dean Blumberg

“These are not DNA-based vaccines. They’re mRNA based. They do not enter the cell nucleus, where our DNA is. They cannot modify any cell DNA,” Blumberg said. 

He said one of the wildest myths is that the vaccine will introduce non-human DNA into our bodies. That is not possible. 

“There is no DNA of any kind in either vaccine,” Blumberg said. “They don’t change us in any way, except to help us build immunity to COVID-19.” 


Key takeaways

COVID-19 vaccines cause the immune system to make antibodies to fight the COVID-19 virus.

The Food and Drug Administration (FDA) has given emergency use authorization to two types of COVID-19 vaccines and approval to one vaccine. Coronaviruses have a spikelike structure on their surface called an S protein. Messenger RNA (mRNA) vaccines give your cells instructions to build a harmless piece of an S protein. Viral vector vaccines place genetic material from the COVID-19 virus into a modified version of a different virus. When this different virus enters your cells, it delivers genetic material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Both vaccines then cause the immune system to make antibodies to fight the COVID-19 virus.

John Hopkins

MYTH: The messenger RNA technology used to make the COVID-19 vaccine is brand new.

FACT: The mRNA technology behind the new coronavirus vaccines has been in development for almost two decades.


Vaccine makers created the technology to help them respond quickly to a new pandemic illness, such as COVID-19.

John Hopkins

MYTH: The COVID-19 vaccine was developed with or contains controversial substances.

FACT: The first two COVID-19 vaccines to be authorized by the FDA contain mRNA and other, normal vaccine ingredients, such as fats (which protect the mRNA), salts, as well as a small amount of sugar.


These COVID-19 vaccines were not developed using fetal tissue, and they do not contain any material, such as implants, microchips or tracking devices.


Fact: There is no microchip and no tracking device of any kind in either vaccine.

This debunked myth morphed into a conspiracy theory after Bill Gates suggested creating a digital certificate of vaccine records. Gates, in fact, has been the top subject of COVID-19 misinformation since early in the pandemic, according to media analysis company Zignal Labs. 

“It’s almost hard to deny this stuff because it’s so stupid or strange that even to repeat it gives it credibility,” Gates said in June on a call with reporters to announce The Bill & Melinda Gates Foundation’s $1.6 billion pledge to global vaccine alliance Gavi, according to Business Insider.

Mayo Clinic

Myth: The COVID-19 vaccine was developed as a way to control the general population either through microchip tracking or nano transducers in our brains. 

Fact: There is no vaccine "microchip" and the vaccine will not track people or gather personal information into a database.


This myth started after comments made by Bill Gates from The Gates Foundation about a digital certificate of vaccine records. The technology he was referencing is not a microchip, has not been implemented in any manner and is not tied to the development, testing or distribution of the COVID-19 vaccine. 

Myth: The COVID-19 vaccine will alter my DNA.

Fact: The first COVID-19 vaccines to reach the market are likely to be messenger RNA (mRNA) vaccines.


According to the CDC, mRNA vaccines work by instructing cells in the body how to make a protein that triggers an immune response. Injecting mRNA into your body will not interact or do anything to the DNA of your cells. Human cells break down and get rid of the mRNA soon after they have finished using the instructions.

Myth: COVID-19 vaccines were developed using fetal tissue.

Fact: Neither the Pfizer/BioNTech COVID-19 vaccine nor the Moderna COVID-19 vaccines contain fetal cells nor were fetal cells used in the development or production of either vaccine.

bottom of page