Fully vaccinated patients with cancer who had breakthrough COVID-19 infections remain at high risk for hospitalisation and death, according to a study.

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The study, published in the journal Annals of Oncology showed that fully vaccinated patients who experienced breakthrough infections had a hospitalisation rate of 65 per cent, an ICU or mechanical ventilation rate of 19 per cent, and a 13 per cent death rate. "Patients with cancer who develop breakthrough COVID-19 even following full vaccination can still experience severe outcomes, including death," said Toni Choueiri, Director of the Lank Center for Genitourinary Care at Dana-Farber Cancer Institute. "That is why a multilayered approach that includes masking and social-distancing, along with vaccination plus booster against COVID-19 remains an essential approach for the foreseeable future," Choueiri added.

The data were collected between November 1, 2020, and May 31, 2021, before booster vaccines were recommended for patients with cancer. "Because measures of immunity are not routinely collected in clinical care, we don't know whether these were patients who mounted effective immune responses after vaccination, a lot of emerging data have suggested that patients with cancer, especially blood cancers, don't mount adequate protective antibody responses," said Jeremy Warner, Associate Professor at Vanderbilt-Ingram Cancer Center.

"It's important to note that many of the same factors that we identified prior to the availability of vaccination, age, comorbidities, performance status, and progressing cancer still seem to drive many of the bad outcomes," he noted. The team identified 1,787 patients with cancer and COVID-19 for the study, the vast majority of which were unvaccinated.

The number of fully vaccinated was 54, and 46 per cent of those fully vaccinated had reduced levels of lymphocytes - the T cells and B cells responsible for immunological responses to viruses. Lymphopenia commonly occurs in patients with cancer receiving anti-CD20 monoclonal antibodies or CAR-T-cell treatments for hematologic malignancies, including lymphoma and leukaemia.

The study appears to support previous observations that patients with hematologic malignancies are at greater risk for severe outcomes from COVID-19.

However, the number of patients in the study is too small to make definitive conclusions about specific types of anticancer therapies that might be associated with breakthrough infections, the researchers noted. Patients on a treatment regimen of corticosteroids also appeared to be more susceptible to hospitalisation.