Background: Cancer patients are at high risk of infections and vaccination against SARS CoV-2 virus is essential to reduce the risk of COVID-19 and its complications. Different types of vaccines against SARS CoV-2 have been developed at record speed, followed by emerging efficacy studies of these vaccines. Our aim is to assess the efficacy of these vaccines in Indian cancer patients, along with factors such as intervals between doses impacting a robust immune response. Methods: A longitudinal observational study was done to evaluate the seroconversion post one and/or two doses of ChAdOx1 nCoV-19 (Covishield) and BBV152 (Covaxin) vaccine in adult cancer patients. Patients received 0.5 ml of vaccine 4 – 12 weeks apart based on existing Government regulations. A minimum gap of four weeks post vaccination for sample collection was followed. Samples were collected during patient follow up or treatment schedules. The control group comprised of healthy volunteers. Our primary endpoint was to assess seroconversion rates to SARS COV-2 spike protein after first and/or second dose. Our secondary endpoint was to explore the factors influencing seroconversion and to compare the two available vaccines in India, Covishield and Covaxin. Results: Between May 1, 2021 and January 16, 2022, antibody levels were measured in 219 patients after second dose and 56 patients after each dose. The mean age was 57.6+12.2 years (24-85 years) with 52% above 60 years age, and 68% being women. Most common cancer was breast (39.3%) followed by GIT (17.4%), while 44% had metastatic disease. Overall, 54.3% had not received any systemic therapy in the past 6 months, while 22.4% had received chemotherapy and 14.2% had received biologics. Three fourth of the patients had received Covishield and the rest Covaxin. Amongst the 56 patients who had antibody testing after both doses, seroconversion after first and second dose were 85.7% and 96.4% respectively. Higher seroconversion was seen in younger age group, treated with biologics without chemotherapy. In 219 patients, post second dose, seroconversion was marginally higher in women compared to men (96.6% vs 91.4%), on biologics (96.8%) when compared to patients taking chemotherapy (89.8 %), although not statistically significant. Overall patients on Covishield vaccine showed higher seroconversion, compared to Covaxin (P = 0.002) (OR- 5.9). Timing of antibody sample had no effect on seroconversion. Conclusions: Both Covishield and Covaxin are immunogenic in cancer patients. Seroconverison after first and second doses were 85.7% and 96.4%with higher rates amongst patients on biologics compared to chemotherapy. We are hoping to continue our study longitudinally to further explore factors impacting efficacy amongst these two vaccines.