Healthy You

Third Dose of COVID Vaccine

What Do Cancer Patients Need to Know?

By Shahzad Mustafa, M.D.

Dr. Mustafa is a member of the Coalition’s Board of Directors. We thank him for sharing his expertise on this timely topic.

As most people have heard, the FDA recently announced expanded emergency use authorization (EUA) for a third dose of the mRNA COVID vaccines (Pfizer and Moderna) for individuals with compromised immune systems. This has since been endorsed by the CDC’s Advisory Committee on Immunization Practices (ACIP). Approximately three percent of Americans, or ten million people, qualify for a third dose based on these guidelines. Although there is some debate as to the specific health conditions that cause immune compromise, patients on chemotherapy for all cancers qualify for a third dose of a COVID vaccine under these guidelines. This most recent recommendation has raised many questions, some of which will be addressed below.

Why get a third dose of either the Pfizer or Moderna COVID vaccine?
Early studies are showing that patients with certain conditions, including those with breast and gynecologic cancers who are being treated with chemotherapy, make lower levels of antibodies from COVID vaccines as compared to people without these conditions. Studies have shown that a third dose of a COVID vaccine in patients with organ transplant increases the immune response and leads to higher levels of antibodies against COVID. This information likely applies to patients being treated with chemotherapy for other cancers as well. Even in patients who did not make an adequate antibody response to the first two doses of the COVID vaccine, the third dose may lead to higher antibody levels and increased protection against COVID.

Is a third dose safe for patients with breast or gynecologic cancer?
In general, additional doses of vaccines do not pose significant health concerns or an increased risk of side effects. This appears to be true for COVID vaccines as well, and a third dose has been shown to be well tolerated in patients with compromised immune systems. Those with breast or gynecologic cancer on chemotherapy who receive a third vaccination should expect to experience side effects similar to doses one and two; most commonly pain at the injection site, fatigue, and muscle aches that last twenty-four hours.

Does a booster imply patients will need additional doses every year, or even sooner?
The term “booster” implies the need to boost the immune response at specific intervals, for example, every eight to twelve months. Our immune system has memory, and antibodies tend to last far beyond that time frame, with most antibodies lasting for many years. Therefore, the term “booster” is a bit misleading, since frequent doses (such as annually) are unlikely to be necessary. It is more likely this third dose represents a three-dose series of vaccination, which we hope will provide long lasting immune protection. This is similar to what is already done with certain childhood vaccinations, such as hepatitis B.

Who is most likely to get a good response from a third dose of a COVID vaccine?
Many factors go into determining a patient’s immune response to vaccination, including the stage of the underlying disease. Patients with early or localized breast or gynecologic cancer are likely to respond better to vaccination as compared to patients with advanced disease on aggressive chemotherapy. Given the difficulty in predicting a person’s immune response, all cancer patients on chemotherapy are advised to receive a third dose of a COVID vaccine, since the risk of significant side effects is very low. The upside is increased protection from significant COVID-19 infection.

Should I get my antibody levels tested to determine if I responded to the vaccine?
Although antibody levels are routinely checked by immunologists to evaluate a patient’s immune system, there are a lot of unknowns on how to best interpret antibody testing for COVID. A test showing no antibodies is suggestive of a poor immune response. However, a test showing the presence for antibodies against COVID does not necessarily prove protection, since the optimal level of antibodies remains unknown. Additionally, antibody levels can fluctuate over time and do not necessarily assure protection in the future. For these reasons, even though antibody testing is not recommended for routine use, people with breast or gynecologic cancer on chemotherapy may wish to discuss the utility of testing on a case by case basis with their oncologist or immunologist.

How should I proceed if I get a third dose of a COVID vaccine and still do not mount an immune response?
Patients with immune compromising conditions would likely benefit from additional risk mitigation techniques, such as wearing a mask in indoor public spaces, avoiding large crowds, maximizing hand hygiene, etc. Additional therapies to provide protection to those who cannot respond to the vaccine are also being studied, with early but promising results. For individuals with immune compromise who have been vaccinated but still get COVID, early treatment with monoclonal antibodies can decrease the risk of severe disease and hospitalization. All patients should discuss these options with their oncologist.