The impact of COVID-19 on cancer patients

The COVID-19 pandemic poses a significant challenge for individuals with compromised immune systems, such as patients with cancer, as they face a heightened susceptibility to severe infections compared to the general population. Such severe infections substantially increase the risk of morbidity and mortality among these patients. Notable risk factors for mortality include advanced age (> 70 years), current or past smoking history, advanced disease stage, the use of cytotoxic chemotherapy, and an Eastern Cooperative Oncology Group (ECOG) score of 2 or higher. Multiple types of vaccines have been developed and implemented, demonstrating remarkable efficacy in preventing infections. However, there have been observable reductions in their ability to elicit an immune response, particularly among individuals with hematological malignancies. The situation becomes more challenging due to the emergence of viral variants of concern (VOCs). Despite the increase in neutralizing antibody levels after vaccination, they remain lower in response to these evolving variants. The need for booster vaccinations has become apparent, particularly for this vulnerable population, due to the suboptimal immune response and waning of immunity post-vaccination. Examining and comprehending how the immune system reacts to various vaccination regimens for SARS-CoV-2 and its VOCs in cancer patients is crucial for designing clinical and public health strategies. This review aims to provide an updated overview of the effectiveness of COVID-19 vaccines in cancer patients, including those undergoing treatments such as hematopoietic stem cell transplantation (HCT) or chimeric antigen receptor (CAR) T cell therapy, by exploring the extent of both humoral and cellular immune responses to COVID-19 vaccination. Furthermore, it outlines risk factors and potential biomarkers that are associated with severe SARS-CoV-2 infection and vaccine responses, and offers suggestions for improving SARS-CoV-2 protection in cancer patients.