Antibody response to three‐dose anti‐SARS‐CoV‐2 mRNA‐vaccination in treated solid cancer patients

Solid cancer patients are at higher risk of SARS‐CoV‐2 infection and severe complications. Moreover, vaccine‐induced antibody response is impaired in patients on anticancer treatment. In this retrospective, observational, hypothesis‐generating, cohort study, we assessed the antibody response to the third dose of mRNA vaccine in a convenience sample of patients on anticancer treatment, comparing it to that of the primary two‐dose cycle. Among 99 patients included, 62.6% were ≥60 years old, 32.3% males, 67.7% with advanced disease. Exactly 40.4% were receiving biological therapy, 16.2% chemotherapy only and 7.1% both treatments. After the third dose, seroconversion rate seems to increase significantly, especially in non‐responders to two doses. Heterologous vaccine‐type regimen (two‐dose mRNA‐1273 and subsequent tozinameran or vice versa) results in higher antibody levels. This explorative study suggests that repeated doses of mRNA‐vaccines could be associated with a better antibody response in this population. Furthermore, heterologous vaccine‐type three‐dose vaccination seems more effective in this population. Since this is a hypothesis‐generating study, adequately statistically powered studies should validate these results. What's new? People with cancer have a higher risk of SARS‐CoV‐2 infection and severe complications, and cancer treatments can reduce the protective effect of vaccines. Here, the authors tested the antibody response to the third dose of mRNA vaccine in 99 patients undergoing treatment for cancer. They found that the third dose stimulated antibody production in nearly all the patients, including those who failed to produce antibodies after the first two doses. Varying the vaccine type for the third dose, from tozinameran to mRNA‐1273 or vice versa, increased the antibody response.