Breakthrough SARS-CoV-2 infections among vaccinated cancer patients were more common during the initial part of the omicron wave than during the delta wave, according to a study published in Cancer Cell.

Researchers analyzed the occurrence of SARS-CoV-2 breakthrough infections in patients with cancer in Austria and Italy between February 24, 2020, and February 28, 2022. 

The team compared rates of breakthrough infections between the delta wave (October 1, 2021, to December 31, 2021) and the initial part of the omicron wave (January 1, 2022, to February 28, 2022).

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Of the 3959 patients studied, 76.7% had a solid tumor malignancy and 23.3% had a hematologic malignancy. 

Most patients were vaccinated — 2.6% with 1 dose, 15.5% with 2 doses, 67.0% with 3 doses, and 0.1% with more than 3 doses. In all, 24.0% of patients tested positive for SARS-CoV-2 at least once. 

Breakthrough Infections, Hospitalizations

The rate of breakthrough infections was 43.2% (54/125) during the delta wave and 70.6% (204/289) during the omicron wave (odds ratio [OR], 3.15; 95% CI, 1.99-4.99; P <.001).

Breakthrough infections during both waves were more frequent in patients with cancer undergoing systemic antineoplastic treatment, compared with patients not receiving ongoing anticancer therapy — 83.2% and 56.1%, respectively (OR, 3.85; 95% CI, 2.12-7.39; P <.001).

Hospital admissions were less common during the omicron wave than during the delta wave, regardless of patients’ vaccination status. Vaccinated patients had a tendency for shorter hospital stays when compared with unvaccinated patients, but the difference between the groups was not significant (P =.126). 

The researchers were not able to determine whether reduced hospitalization rates during the omicron wave were attributable to the seemingly lower pathogenicity of the omicron variant or increasing vaccination coverage.

Immunity Against Variants

The researchers conducted an additional analysis to assess humoral immunity against variants of concern (VOCs) after SARS-CoV-2 vaccination in a subgroup of 78 patients with cancer undergoing antineoplastic treatment. 

The group included 28 patients with solid tumors, 26 with hematologic malignancies who were receiving B cell-targeted treatments, and 24 with hematologic malignancies who were receiving other therapies. The researchers also included 25 healthcare workers (HCWs) as controls.

The researchers compared levels of antibodies specific for the receptor-binding domain (RBD) on the spike protein of VOCs and wild-type SARS-CoV-2. For the wild-type strain, delta variant, and omicron variant, antibody levels to RBD were lowest in the patients with hematologic cancers who were receiving B cell-targeted treatments, followed by the other patients with hematologic malignancies, the solid tumor patients, and the HCWs. 

The researchers also measured the inhibition of RBD-ACE2 binding. Overall, inhibition was higher among the HCWs than among the patient groups. In addition, inhibition of the omicron RBD-ACE2 interaction was “considerably lower” than inhibition for the wild-type strain and the delta variant. 

“We found immunological evidence of highly impaired vaccine-induced neutralization of the omicron variant but not against the wildtype hu-1 strain and the previous delta VOC in patients with hematologic and solid cancers in comparison to HCW,” the researchers wrote. 

The team suggested that adapted VOC-specific vaccines may be needed to protect hematology/oncology patients and to maintain cancer care during the ongoing COVID-19 pandemic.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Mair MJ, Mitterer M, Gattinger P, et al. Enhanced SARS-CoV-2 breakthrough infections in patients with hematologic and solid cancers due to omicron. Cancer Cell. Published online April 12, 2022.