For Cancer Patients, COVID-19 Booster Shots Are Critical


The Context: A common side effect of chemotherapy is that it attacks immune cells needed to fight infections in addition to cancer cells, leaving cancer patients in an ‘immunocompromised’ state. As the COVID-19 vaccine clinical trials largely excluded immunocompromised patients, it has been unclear how well cancer patients undergoing chemotherapy would respond to COVID-19 vaccines — a critical question given their higher risk of death from COVID-19.

The Study: Cancer patients show blunted immune responses to the first two doses of the Pfizer COVID-19 vaccine, but a third dose increases their antibody production significantly, finds a new phase 1 clinical trial and study in Nature Medicine led by NYSCF – Robertson Stem Cell Investigator Alumnus Deepta Bhattacharya, PhD, at the University of Arizona.

The Importance: This study highlights the importance of a third COVID-19 vaccine dose to protect cancer patients undergoing chemotherapy from the SARS-CoV-2 virus.

“We wanted to make sure we understand the level of protection the COVID-19 vaccines are offering our cancer patients, especially as restrictions were being eased and more contagious variants were starting to spread,” said Rachna Shroff, MD, chief of gastrointestinal medical oncology at the University of Arizona Cancer Center, director of the Cancer Center Clinical Trials Office, and lead author of the study in an article from University of Arizona News.

The team examined 53 cancer patients and 50 healthy adults, measuring immune responses following a first and second dose of the Pfizer COVID-19 vaccines. They began their studies shortly after the Pfizer vaccine was approved in 2020, and focused on patients with solid tumors, such as breast or gastrointestinal cancer, and excluded people on immunotherapy.

“We were pleasantly surprised,” said Dr. Bhattacharya, professor of immunobiology in the University of Arizona College of Medicine – Tucson and a member of the Cancer Center and BIO5 Institute. “We looked at antibodies, B cells and T cells, which make up the body’s defense system, and found the vaccine is likely to be at least partially protective for most people on chemotherapy.”

However, the immune response in cancer patients was lower than in healthy controls, and some patients showed no response at all – leaving them with less protection against the virus. This could be especially dangerous as the delta variant continues to spread across the United States.

The team began a phase 1 clinical trial, in which twenty cancer patients then received a third dose of the Pfizer vaccine. Nearly all (16) saw immune responses (antibody levels) jump to those observed in healthy people who received two doses. This points to the importance of booster shots for people undergoing chemotherapy, to mitigate their elevated vulnerability to COVID-19.

Learn more about boosters, vaccines for children, and the future of the pandemic at a conversation with Dr. Bhattacharya on November 10 at 4 PM ET.

Journal Article:

Immune responses to two and three doses of the BNT162b2 mRNA vaccine in adults with solid tumors
Rachna T. Shroff, Pavani Chalasani, Ran Wei, Daniel Pennington, Grace Quirk, Marta V. Schoenle, Kameron L. Peyton, Jennifer L. Uhrlaub, Tyler J. Ripperger, Mladen Jergović, Shelby Dalgai, Alexander Wolf, Rebecca Whitmer, Hytham Hammad, Amy Carrier, Aaron J. Scott, Janko Nikolich-Žugich, Michael Worobey, Ryan Sprissler, Michael Dake, Bonnie J. LaFleur & Deepta Bhattacharya. Nature Medicine. 2021. DOI:

Cover image credit: University of Arizona Health Sciences, Noelle Haro-Gomez

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