In a recent study published in the Journal of the American Medical Association (JAMA) Oncology, researchers examined the risk of breakthrough coronavirus disease 2019 (COVID-19) infections, hospitalizations, and mortality among COVID-19-vaccinated cancer patients.
Before the introduction of the COVID-19 vaccination, studies reported that cancer patients were at an elevated risk for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and severe disease. Although vaccines against SARS-CoV-2 have been effective in real-world settings, breakthrough infections have often been documented.
According to one study, cancer patients or those undergoing anti-cancer treatment demonstrated poor immune responses following messenger ribonucleic acid (mRNA) vaccine administration, compared to healthy controls.
In contrast, another study observed that these population sub-groups developed adequate immunity in response to vaccination. Nonetheless, not much is known about COVID-19 breakthrough cases, hospitalization, and mortality of vaccinated cancer patients.
About the study
In the current study, researchers analyzed the electronic health records of vaccinated patients with cancer and characterized breakthrough SARS-CoV-2 cases, hospitalization, and mortality among this subset of the population.
The study population had been diagnosed with at least one of the 12 most common cancers in the United States – bladder, colorectal, breast, lung, liver, endometrial, hematologic, pancreatic, skin, prostate, and thyroid cancers.
A control group with vaccinated subjects without any cancer diagnoses was instituted. Eligible participants had evidence of COVID-19 vaccination between December 2020 and November 2021 with no history of SARS-CoV-2 infection before vaccination.
The monthly incidence and the cumulative risk of breakthrough cases were also estimated. The authors assessed if cancer increased the risk for breakthrough infections and whether the risk profiles differed between those who had medical encounters with cancer in the past year and those who did not. Additionally, the risk of hospitalization and mortality in breakthrough cases was investigated relative to non-breakthrough cases.
Breakthrough infections were compared between cancer and non-cancer patients after propensity score matching for demographics, social determinants of health (SDOHs), comorbidities, and vaccine types (mRNA or adenoviral-vectored vaccines). Similarly, propensity scores were matched for the corresponding parameters between those with a history of a medical encounter with cancer within one year and those without.
The study population comprised 45,253 vaccinated patients with cancers, and the control group had over 0.59 million vaccinated patients without cancers. The mean age of cancer patients was 68.7 years, and 53.5% of them were females. About 74.1% were White individuals, 15.4% were Black, 4.9% were Hispanic, and 3.8% were Asian. In the control group, the mean age was 51.1 years, 55.1% of them were females, and over 62%, 14.2%, 12.2%, and 8.3% were White, Black, Hispanic, and Asian, respectively.
The monthly incidence rates of breakthrough infections increased steadily in the study period across both cohorts but were significantly higher in the cancer patients than in the controls. The cumulative risk for cancer patients was 13.6% compared to 4.9% for the controls. The highest risks were noted among patients diagnosed with pancreatic cancers (24.7%) and liver cancers (22.8%), and the lowest risk was observed among those diagnosed with thyroid cancer (10.3%). This indicates that cancer was a risk factor for breakthrough infections among the vaccinated cohort.
Likewise, the risk of breakthrough infections was higher among individuals with a recent medical encounter with cancer within a year than those who did not have a history of medical encounters.
Overall, the risk of hospitalization for cancer patients with breakthrough infections was 31.6% compared to 3.9% for those without breakthrough infections. Likewise, the corresponding mortality risks were 6.7% and 1.3%, respectively. Among the control patients, the risk of hospitalization was 25.9% in patients who had breakthrough infections compared to 3% in the non-breakthrough cohort and the corresponding mortality risks were 2.7% and 0.5%, respectively.
The study findings showed that breakthrough infections increased during the study period among cancer and non-cancer patients, indicating the waning of immune responses following vaccination, and that cancer was a risk factor. Notably, the incidence of breakthrough infections was higher in cancer patients than in controls, reflecting their increased susceptibility or less protective nature of COVID-19 vaccines among this population group.
Additionally, breakthrough infections were significantly associated with hospitalization and mortality risk among SARS-CoV-2-vaccinated cancer patients, emphasizing the indispensable need to follow mitigation or preventive measures.