Patients with solid tumors have been a risk group since the beginning of the SARS‐CoV‐2 pandemic due to more significant complications, hospitalizations or deaths. The immunosuppressive state of cancer treatments or the tumor itself could influence the development of post‐vaccination antibodies. This study prospectively analyzed 89 patients under chemotherapy and/or immunotherapy, who received two doses of the mRNA‐1237 vaccine, and were compared with a group of 26 non‐cancer individuals. Information on adverse events and neutralizing antibodies against the ancestral strain of SARS‐CoV‐2 (WH1) have been analyzed. Local reactions accounted for 65%, while systemic reactions accounted for 46% of oncologic individuals/cancer patients. Regarding the response to vaccination, 6.7% of cancer patients developed low neutralizing antibody levels. Lower levels of neutralizing antibodies between cancer and non‐cancer groups were significant in individuals without previous SARS‐CoV‐2 infection, but not in previously infected individuals. We also observed that patients receiving chemotherapy or chemoimmunotherapy have significantly lower levels of neutralizing antibodies than non‐cancer individuals. In conclusion, our study confirms the importance of prioritizing cancer patients receiving anticancer treatment in SARS‐CoV‐2 vaccination programs. Cancer patients are a risk group for SARS‐CoV‐2 infection. We determined the levels of anti‐SARS‐CoV‐2 plasma neutralizing antibodies post mRNA‐1273 vaccination and observed that cancer patients exhibit lower titers compared to non‐cancer individuals, particularly in individuals not previously infected by SARS‐CoV‐2. Additionally, we found an association between low levels of neutralizing antibodies and chemotherapy‐containing treatments, highlighting their prioritization in SARS‐CoV‐2 vaccination programs.