evidence: The Moderna and Pfizer BioNTech vaccines prevented COVID-19 infection in cancer patients, particularly in those whose treatment concluded more than six months before vaccination, say researchers at Stanford, Harvard and the VA. [...] The mRNA-based COVID-19 vaccines are effective at preventing infection in most cancer patients, according to a nationwide study of veterans diagnosed with cancer in the past decade. [...] The researchers studied the medical records of more than 180,000 VA patients who received systemic, or whole-body, treatments, including chemotherapy or hormone therapy, between August 2010 and May 2021. The patients’ median age was 73.7, and 94% were men. Of these, about 113,000 were vaccinated with one of the two mRNA-based vaccines approved by the Food and Drug Administration — Pfizer BioNTech and Moderna — between Dec. 15, 2020, and May 4, 2021. (People who had been previously diagnosed with COVID-19 were excluded from the study, as were those who received the adenovirus-based vaccine produced by Johnson & Johnson.)