COVID-19 Vaccine Coverage and Adverse Event Among Cancer Patients During the 2021-2022 SARS-CoV-2 Outbreaks in Thailand: A Retrospective Cohort Study.

Immunocompromised individuals, particularly cancer patients, face elevated risks from COVID-19 and have been prioritized for vaccination in Thailand. However, evidence regarding vaccine coverage and safety in this population remains limited. This study aimed to evaluate COVID-19 vaccination coverage and safety among cancer patients by analyzing the frequency, severity, and risk factors of adverse events following immunization (AEFI). A retrospective cohort of 14,430 patients receiving care at Lopburi Cancer Hospital between January 2021 and December 2022 was analyzed. Demographic and clinical data, vaccination status, and AEFI were obtained from hospital electronic medical records and the national “Mor Prom” digital health platform. Multivariable logistic regression identified factors associated with AEFI. Of the 14,430 patients, 78% received at least one-vaccine dose, and 42% received a booster (> standard two doses). Vaccine sequences varied by following as inactivated vaccines predominated for the first dose (49%), viral vectors for the second (49%), and mRNA for the third (33%). AEFI reports were mostly mild, including fever, injection site reactions, headache, and myalgia. Multivariable analysis identified younger age, female sex, and viral vector vaccines as significant predictors for AEFI. Conversely, metastatic or locally advanced cancer stages were associated with lower odds of adverse events. No severe adverse events exceeded 5% in any group. Considering AEFI, this study suggested that the COVID-19 vaccination demonstrated a favorable safety profile among Thai cancer patients, with manageable adverse events. The findings supported the continued prioritization of vaccination in vulnerable population and provided evidence to alleviate patient concerns regarding vaccine safety.