Fact-check: 9 myths about the COVID-19 vaccines

Last update March 8, 2021

Myths and misconceptions about the COVID-19 vaccines may be impacting the decisions you make about whether to get vaccinated – or what to do once you’ve gotten the vaccine.

To help separate fact from fiction, we asked our medical experts to weigh in on several common myths and misconceptions surrounding the COVID-19 vaccines.

1. Myth: You shouldn’t get a COVID-19 vaccine if you’re currently receiving cancer treatment.

Fact: After carefully reviewing all available data on these vaccines, MD Anderson medical experts have determined that COVID-19 vaccines are safe and recommended for current and former cancer patients.

There are no safety concerns about vaccination for patients who are currently receiving cancer treatment, but the vaccines will likely be more effective if timed in coordination with your treatment schedule. Your oncologist can help you decide when the right time is to be vaccinated, to maximize the chances that you'll get the full benefit of the vaccine.

If you’re currently receiving chemotherapy, immunotherapy, CAR T-cell therapy, stem cell transplants or are enrolled in a clinical trial, check with your provider about vaccine appointment timing. Patients who have recently had surgery should wait for 2 weeks after their surgery date to receive the vaccine.

All other patients can go ahead and schedule a COVID-19 vaccine appointment without contacting their provider for further guidance.

2. Myth: I can’t spread COVID-19 to others once I’ve been vaccinated.

Fact: “While we know the vaccine will protect against COVID-19 disease, we don't know yet whether it will protect against asymptomatic transmission of the coronavirus, which would allow you to pass on the virus to another individual,” says infectious diseases specialist David Tweardy, M.D.

“Our national COVID-19 vaccine supply is still limited right now and not everyone around you will be able to get vaccinated right away,” adds Tereffe, “so until all of us have the opportunity to be vaccinated and reach a level of herd immunity, masking, hand washing and social distancing are the best ways to keep everybody else safe.”

3. Myth: The Pfizer and Moderna vaccines contain a live coronavirus that can make me sick.

Fact: Both of these vaccines use mRNA technology. The vaccines do not include a live virus.

You may experience side effects of the vaccine, but you're not going to get the actual virus from the vaccine.

4. Myth: The vaccines were produced too quickly to be safe.

Fact: Medical experts were involved in every step of the development of these vaccines. No corners were cut in their development or the trials that showed that they worked.

In order to be authorized by the Food and Drug Administration, a vaccine has to be at least 50% effective at preventing symptomatic infection. The Pfizer and Moderna vaccines are 95% effective at preventing symptomatic infection. Johnson & Johnson's Janssen vaccine was 67% effective overall in preventing moderate to severe COVID-19.

“Using mRNA for vaccines to prevent viral infections has been studied for years,” says Tweardy of the technology used for the Pfizer and Moderna vaccines. “Part of the reason researchers were able to develop these vaccines so quickly is because COVID-19 is caused by a coronavirus similar to SARS and MERS, and researchers were able to build upon previous work creating mRNA vaccines for these viruses as they searched for a vaccine against COVID-19.”

5. Myth: You don’t need the second vaccine dose of the Pfizer or Moderna vaccines.

Fact: “If you’re getting the Moderna or Pfizer vaccine, you need to get both doses. The data from the clinical trials for these vaccines established that the second dose really achieves a much higher level of protection than the first dose alone,” says Tweardy.

The Pfizer vaccine is delivered in two separate doses that are given 3 weeks apart. The Moderna vaccine is delivered in two separate doses given 4 weeks apart.

6. Myth: The vaccine will cause you to test positive for COVID-19.

Fact: If you take the vaccine and you don’t have a COVID-19 infection, you should not test positive for the coronavirus on a PCR or antigen test since this inactivated vaccine does not contain the SARS-CoV-2 virus. If you take a COVID-19 test and it’s positive after your first dose or second dose of vaccine, you have an active infection and may have been exposed to someone with the coronavirus.

She adds that any time you test positive for COVID-19, stay home and contact your health care provider for guidance.

7. Myth: You don’t need to get vaccinated if you’ve already had COVID-19.

Fact: “If you’ve been diagnosed in the past with COVID-19, we recommend that you still get the vaccine because the vaccine will help to boost your immunity even further than the infection itself,” says Tweardy.

He adds that if you had a symptomatic COVID-19 infection, make sure you recover and finish your quarantine before getting the vaccine. If you were given monoclonal antibody therapy or convalescent plasma as a treatment, you should wait 90 days before receiving any COVID-19 vaccine.

8. Myth: The mRNA COVID-19 vaccines will alter your DNA.

Fact: “These vaccines do not change or affect your DNA,” says Tweardy of the Pfizer and Moderna vaccines. “These vaccines teach your cells to produce proteins that train your immune system to create antibodies that help the body fight off infection. They don’t interact with your DNA at all.”

9. Myth: The COVID-19 vaccines have severe side effects.

Fact: The side effects for the COVID-19 vaccines are very similar to those that people experience when they get the flu shot. If you've had the flu shot and you've done OK, you'll probably do just fine with the COVID-19 vaccine.

People who receive the vaccines may experience some short-term side effects, such as arm pain, fatigue and headaches right after the injection.

More serious side effects are rare. In a very small number of people, a serious allergic reaction could happen after vaccination. But so far, the number of people who've had this kind of reaction is very small, compared to the millions of people who've now been vaccinated. The benefits of getting the vaccine far exceed the risks of having an allergic reaction, especially for those at high-risk for severe infection, such as cancer patients.

Learn more about the COVID-19 vaccines.