BACKGROUND Cancer patients are considered a priority group for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination given their high risk of contracting severe coronavirus disease 2019 (COVID-19). However, limited data exists regarding the efficacy of immunization in this population. In this study we assess the immunologic response after COVID-19 vaccination of cancer versus non-cancer population. METHODS PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science databases were searched from March 01, 2020, through August 12, 2021. Primary endpoints were anti-SARS-CoV-2 spike protein (S) immunoglobulin G (IgG) seroconversion rates, T-cell response, and documented SARS-CoV-2 infection after COVID-19 immunization. Data was extracted following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines. Overall effects were pooled using random effects models. RESULTS This systematic review and meta-analysis included 35 original studies. Overall, 51% (95% confidence interval [CI], 41-62) and 73% (95%CI, 64-81) of cancer patients developed anti-S IgG above the threshold level after partial and complete immunization, respectively. Patients with hematologic malignancies had a significantly lower seroconversion rate than those with solid tumors after complete immunization (65% vs 94%; P <0.0001). Compared to non-cancer controls, oncological patients were less likely to attain seroconversion after incomplete (RR 0.45 [95%CI 0.35-0.58]) and complete (RR 0.69 [95%CI 0.56-0.84]) COVID-19 immunization schemes. Cancer patients had a higher likelihood of having a documented SARS-CoV-2 infection after partial (RR 3.21; 95%CI 0.35-29.04) and complete (RR 2.04; 95%CI 0.38-11.10) immunization. CONCLUSIONS Cancer patients have an impaired immune response to COVID-19 vaccination compared to controls. Strategies that endorse the completion of vaccination schemes are warranted. Future studies should aim to evaluate different approaches that enhance oncological patients’ immune response.

The COVID-19 pandemic has had a substantial effect on cancer care. 1 The recent widespread availability of vaccines against SARS-CoV-2 is a promising strategy to prevent COVID-19associated mortality. However, previous reports have shown a high hesitancy rate to receive a COVID-19 vaccine among oncologic patients. 2,3 Because breast cancer is the most commonly diagnosed malignant neoplasm, 4 it is imperative to evaluate the specific concerns regarding COVID-19 vaccination among patients with this disease.Methods | From March 12 to March 26, 2021, any woman with breast cancer residing in Mexico who visited the social media channels of nongovernmental organizations dedicated to improving breast cancer care were invited to complete a webbased survey. To assess COVID-19 vaccine hesitancy rates, participants were dichotomized into a vaccine-acceptant group (ie, willing to be vaccinated immediately) and a vaccinehesitant group (ie, prefer to wait, only if vaccine is mandatory, or refuse). Respondents who previously had been vaccinated against COVID-19 were excluded from the statistical analysis.Data analyses were performed using SPSS, version 27 (IBM Inc). Significance was defined as 2-tailed P < .05. The

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