• Matilda Xinwei Lee, Siyu Peng, Ainsley Ryan Yan Bin Lee, Shi Yin Wong, Ryan Yong Kiat Tay, Jiaqi Li, Areeba Tariq, Claire Xin Yi Goh, Ying Kiat Tan, Benjamin Kye Jyn Tan, Chong Boon Teo, Esther Chan, Melissa Ooi, Wee Joo Chng, Cheng Ean Chee, Carol L F Ho, Robert John Walsh, Maggie Wong, Yan Su, Lezhava Alexander, Sunil Kumar Sethi, TanShaun Shi YanSSY, Yiong Huak Chan, Kelvin Bryan Tan, Soo Chin Lee, Louis Yi Ann Chai, and Raghav Sundar.
• Department of Haematology-Oncology, National University Cancer Institute, Singapore, Singapore.
• Ann Acad Med Singap. 2023 Jan 1; 52 (1): 8168-16.

IntroductionThree doses of SARS-CoV-2 mRNA vaccines have been recommended for cancer patients to reduce the risk of severe disease. Anti-neoplastic treatment, such as chemotherapy, may affect long-term vaccine immunogenicity.MethodPatients with solid or haematological cancer were recruited from 2 hospitals between July 2021 and March 2022. Humoral response was evaluated using GenScript cPASS surrogate virus neutralisation assays. Clinical outcomes were obtained from medical records and national mandatory-reporting databases.ResultsA total of 273 patients were recruited, with 40 having haematological malignancies and the rest solid tumours. Among the participants, 204 (74.7%) were receiving active cancer therapy, including 98 (35.9%) undergoing systemic chemotherapy and the rest targeted therapy or immunotherapy. All patients were seronegative at baseline. Seroconversion rates after receiving 1, 2 and 3 doses of SARS-CoV-2 mRNA vaccination were 35.2%, 79.4% and 92.4%, respectively. After 3 doses, patients on active treatment for haematological malignancies had lower antibodies (57.3%±46.2) when compared to patients on immunotherapy (94.1%±9.56, P<0.05) and chemotherapy (92.8%±18.1, P<0.05). SARS-CoV-2 infection was reported in 77 (28.2%) patients, of which 18 were severe. No patient receiving a third dose within 90 days of the second dose experienced severe infection.ConclusionThis study demonstrates the benefit of early administration of the third dose among cancer patients.

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