A COVID-19 vaccine booster shot gives cancer patients — especially those with blood cancer — much-needed protection, new research reports.

"Our study demonstrates in clear terms how the booster shot can make all the difference for some people with compromised immune systems, such as people with cancer," study co-author Dr. Balazs Halmos said in a news release from Montefiore Health System in New York City. Halmos is director of the Multidisciplinary Thoracic Oncology Program at Montefiore.

Many cancer patients have weakened immune systems that put them at increased risk of severe illness and death from COVID-19.

In this study, researchers at Montefiore Einstein Cancer Center checked for antibodies in 99 cancer patients just after they'd been fully vaccinated. For most of those who had detectable antibodies at that point, antibody levels had declined when testing was repeated four to six months later.

In the second portion of the study, the investigators assessed 88 cancer patients — 65% with blood cancer and 35% with solid tumors — who were fully vaccinated with the Pfizer (70%), Moderna (25%) or Johnson & Johnson (5%) vaccines.

After vaccination, they were tested for the presence of antiviral antibodies in their blood. Detectable antibodies were found in 64% of them. The remaining patients tested negative for antibodies; all but one had blood cancer.

All then received a booster shot and were retested for antibodies four weeks later. Eighty percent of the patients had higher antibody levels than before their booster shot, including 56% who previously had no detectable antibodies after vaccination.

The findings were published online Nov. 16 in the journal Cancer Cell.

"The speed of recommendations and treatments for COVID-19 has been incredible, but many questions have remained regarding the safety and necessity of booster shots," said study co-author Dr. Lauren Shapiro, a fellow at Montefiore Medical Center and Albert Einstein College of Medicine.

"Our research now gives data-driven answers about when vaccine protection from COVID-19 wanes for immunocompromised individuals and offers clear guidance about the necessity of vaccination for people with cancer," she said in the release.