What to know about the COVID-19 vaccines

Last updated April 8, 2021

As the number of COVID-19 cases continues to increase, you probably have a lot of questions about coronavirus vaccines. Are they safe? Can you still get infected with COVID-19 if you've been vaccinated? How soon will you be able to get a COVID-19 vaccine and get back to some semblance of a normal life? When can cancer patients get vaccinated?

For answers to these COVID-19 vaccine questions and more, we spoke with infectious diseases specialist and head of Internal Medicine David Tweardy, M.D..

Are the COVID-19 vaccines safe for cancer patients?

After careful review of all available scientific evidence, our clinical experts have determined that the COVID-19 vaccines authorized for emergency use by the Food and Drug Administration (FDA) are safe and recommended for former and current cancer patients. 

Patients currently receiving chemotherapy, immunotherapy, CAR T cell therapy, stem cell treatments or participating in clinical trials can still receive the vaccine. Check with your provider for vaccine timing recommendations prior to scheduling. 

The vaccines are safe for patients in treatment but will likely be more effective if timed in coordination with the treatment schedule. 

If you are a current or past breast cancer patient, ask to receive the vaccine in the arm opposite of your breast cancer site. This will help support your immune response and lessen lymph node enlargement. Enlarged lymph nodes can falsely affect cancer screening and diagnostic imaging results up to 6 weeks after vaccination.

Patients who have recently had surgery should wait for 2 weeks after their surgery date to receive the vaccine.

All other patients can proceed to schedule a vaccine appointment without contacting MD Anderson for further guidance. Patients who have received a vaccine at another health care provider should let their care team know.

When will MD Anderson offer the COVID-19 vaccines to patients?

MD Anderson is administering a limited supply of COVID-19 vaccines for our cancer patients. We will vaccinate patients with one of the three COVID-19 vaccines authorized by the FDA, depending on the supply we are given by the state of Texas.

As we receive more vaccine supply, we will invite additional outpatients in phases to self-schedule their COVID-19 vaccine in MyChart. Patients will receive both MyChart message and text notifications when new COVID-19 vaccine clinics are open for self-scheduling. 

It’s important to continue taking precautions such as wearing a mask, maintaining social distancing and washing your hands frequently, even after you receive a COVID-19 vaccine. These precautions will be necessary until public health experts advise otherwise.

Will people who’ve recovered from COVID-19 be able to get vaccinated?

Since reinfection is a possibility, vaccination is expected to provide added protection for those who’ve recovered from COVID-19. However, you should wait to get vaccinated until your symptoms of infection have resolved and you have completed the quarantine period recommended by the CDC. In addition, if you received monoclonal antibody therapy or convalescent plasma to treat your COVID-19 infection, you should wait 90 days after receiving those treatments to be vaccinated.

After symptomatic infection, natural immunity appears to persist for at least 3 months. Therefore, you could choose to defer vaccination for 90 days if you desire. If your infection was asymptomatic, it should not factor into your decision to be vaccinated since you may not have effective immunity.

How do the Pfizer and Moderna vaccines work?

Our cells use messenger RNA (mRNA) to produce the various proteins our bodies need to function. The Pfizer and Moderna vaccines both use an mRNA sequence that codes for the unique spike protein on the surface of the SARS-CoV-2 virus. Once a person receives the vaccine, their cells take up that mRNA sequence and produce the COVID-19 spike protein. Their immune system then detects those proteins as foreign and creates antibodies against them, which helps provide protection from future COVID-19 infections.

Currently, both of these vaccines require two doses given a few weeks apart to be effective.

How does Johnson & Johnson's Janssen COVID-19 vaccine work?

Johnson & Johnson's COVID-19 vaccine uses a modified adenovirus containing the part of the coronavirus' DNA that encodes the spike protein. It targets the really important part of the virus — the protein spikes that stick up like little maces all over its surface — instead of the virus as a whole. It prompts the body to generate the spike protein itself. Once that happens, the immune system recognizes it as an invader and starts developing antibodies against it. So, when the real coronavirus comes along, these antibodies can shut it down. 

Johnson & Johnson's vaccine requires only one dose.

What makes the mRNA approach used by the Pfizer and Moderna vaccines so different from that of previous vaccines?

This is the first time this type of technology has ever been used for a vaccine. And the speed at which it is being developed is truly mind-boggling.

Remember, this particular coronavirus was virtually unknown in November 2019. The actual syndrome caused by it was only first described in December 2019. A month later, scientists had isolated the virus and sequenced its genome. That’s something that used to take a full year or more. Two months later, we had the first COVID-19 vaccine candidates. Four months after that, some were already in Phase III clinical trials. And we’ll have a coronavirus vaccine available to health care workers in December 2020.

We’re living through a modern scientific miracle. Vaccines have not been developed at this speed before. Vaccine development usually takes 10 to 15 years after the identification of a new infectious disease. I’ve been working in infectious diseases for 40 years, and I never would’ve thought it was possible.

Could this same mRNA vaccination method be used again against future coronaviruses?

Absolutely. This strategy has the capacity to almost let us anticipate the next strain of coronavirus so we can be prepared for it, kind of like we do now with the flu.

We could sequence the next coronavirus that’s identified as distinct and separate from this one in a month or less. Once we had that, we could insert the sequence of its spike protein into every step of the vaccine development pathway. That could get us another vaccine for testing within three months.

With this family of coronaviruses, that could potentially allow us to have a vaccine ready before the next one even becomes a pandemic. So theoretically, we could stop the next pandemic in its tracks.

Are the coronavirus vaccines safe?

Yes. I think anyone who gets a coronavirus vaccine that has received an Emergency Use Authorization (EUA) from the Food and Drug Administration (FDA) can have confidence that it will be safe, and that the benefits of being vaccinated will outweigh the risks. Otherwise, it wouldn’t receive an EUA. The FDA has been looking at this very carefully, and each vaccine has had to be tested on a lot of people to get authorized for emergency use.

COVID-19 is caused by a coronavirus similar to SARS and MERS, and researchers were able to build upon previous work creating vaccines for these diseases as they searched for a vaccine against COVID-19. mRNA has been studied for many years in relation to the study of infectious diseases and as an area of opportunity in cancer treatment.

COVID-19 is the third in a series of coronaviruses. After SARS and MERS, we understand the pathogenesis and early aspects of immunity and have learned from those experiences and taken that knowledge to target the weak spot of coronaviruses.

Even more closely watched than the efficacy of the vaccines in the clinical trials is the safety of the participants. For the FDA to consider an application for emergency authorization of a vaccine, more than half of the people enrolled must have been monitored for at least two months. Preliminary data shows the observed side effects are very similar to the flu vaccine, such as pain at the injection site and fatigue.

The FDA’s vaccine advisory committee comprises experts in medicine and research who meet to review the request for EUA of a vaccine, and these experts evaluate the safety and efficacy of the vaccines. Clinical trial participants will continue to be followed even after any EUAs are granted.

Is it safe to get a diagnostic imaging exam, like an MRI or CT scan, after you get a COVID-19 vaccine?

If you need a diagnostic imaging exam that includes your axillary lymph nodes, talk to your doctor to see if it is medically appropriate to delay the exam for 6 to 10 weeks after your COVID-19 vaccination. Your body's immune response to the vaccine may cause temporary inflammation of your axillary lymph nodes and interfere with your imaging exam.

Is it safe to get a COVID-19 vaccine if you're pregnant or breastfeeding?

Safety data isn't yet available on vaccine-associated risks during pregnancy or the effects of COVID-19 vaccines on breastfed infants or on milk production/excretion. In breastfeeding women, mRNA vaccines are not thought to be a risk to the breastfed infant.

The Centers for Disease Control and Prevention (CDC) says pregnant women are at increased risk for severe illness should they get COVID-19, and their babies may be at risk for adverse outcomes like preterm birth. For these reasons, women who are pregnant should consult with their health care providers to evaluate their personal risk of contracting COVID-19 as they consider whether to undergo vaccination. The decision is yours and should be based on available safety information and thoughtful consideration of the risks versus benefits of vaccination.

How long will the coronavirus vaccines be effective?

We’d obviously love for it to give lifelong immunity against COVID-19, but that remains to be seen, as many people in the clinical trials are still in the follow-up period. We believe at least three months, if not six months or more. More data is coming and will guide us for future planning. If I had to guess, I would say it’s probably going to fall somewhere between influenza and the mumps, in terms of longevity of protection. It will probably be closer to the flu, because respiratory viruses don’t tend to lead to long-term immunity. 

What are the chances that a person who gets vaccinated can still get infected with COVID-19?

We know from the data so far that the Moderna and Pfizer vaccines confer about 95% effectiveness after the second dose – meaning there were a few people who still experienced a symptomatic COVID-19 infection after their full course of vaccination. Among those who did experience a symptomatic infection, the vaccine helped prevent serious symptoms and hospitalization. We don’t have meaningful data on asymptomatic infections in the trial groups. That means that we don’t know if vaccinated people could still carry the virus and transmit it to others, without having symptoms themselves.

These are very highly effective vaccines – for comparison, the flu vaccine we get is 50% to 70% effective and it still has a big impact each year. It will take some time, but widespread vaccination have a big impact on slowing the spread of COVID-19.

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