PhD student Department of Industrial Pharmaceutical Science, College of Pharmacy, Ewha Womans University, Republic of Korea
Background: Cancer patients are at a greater risk for SARS-CoV-2 infection and following severe outcomes due to their underlying immunosuppression; however, there is limited evidence available on the effectiveness of COVID-19 vaccination in this patient population.
Objectives: To examine the risk of SARS-CoV-2 infection and the related severe outcomes in cancer patients who completed a primary COVID-19 vaccination series.
Methods: We used the nationwide Korea Disease Control and Prevention Agency-COVID19-National Health Insurance Service cohort database. Among patients diagnosed with COVID-19 from Oct 8, 2020 to Dec 31, 2021, our study included cancer patients identified by ICD-10 codes and special cancer claim codes. First, a self-controlled risk interval (SCRI) design was applied to assess the effectiveness of vaccine against SARS-CoV-2 infection in patients who received 2nd COVID-19 vaccine before Nov 30, 2021. By considering the period of gaining immunity, we defined the exposure window (EW) as 21-25 days after the 2nd dose and the control window (CW) as 3-7 days after the 1st dose. Using a conditional Poisson regression model, we calculated the incidence rate ratio (IRR) of infection adjusted by calendar time. Second, a cohort study design was used to evaluate the risk of severe outcomes related to COVID-19 in cancer patients based on their COVID-19 vaccination status. The risk of severe outcomes was compared between cancer patients who received the 2nd dose of a COVID-19 vaccine and those who were not vaccinated, using 1:1 propensity score matching. The severe outcomes including death, admission to the intensive care unit, and use of artificial respiration were followed up for 30 days after the confirmation of COVID-19. The Cox proportional hazard model was used to calculate the hazard ratio (HR). For comparison, both designs were applied to all COVID-19 patients, including cancer patients.
Results: We identified 579,818 patients diagnosed with COVID-19, of which 14,448 were cancer patients. For the SCRI study, we included 217 cancer patients who received 2nd dose and were confirmed with COVID-19 in EW or CW. The risk of infection in cancer patients was not significantly lower in the periods following the gain of immunity (IRR=0.88, 95% CI: 0.64–1.22) but significantly lower for all COVID-19 patients (IRR=0.58, 95% CI: 0.55–0.61). After matching, each group had 1,998 cancer patients in a cohort study. The adjusted HR of severe outcomes in the vaccination group was 0.27 (95% CI: 0.22-0.34) in cancer patients and 0.19 (95% CI: 0.17-0.20) in all COVID-19 patients.
Conclusions: Despite the COVID-19 vaccine not being fully effective in preventing SARS-CoV-2 infection in cancer patients, the study found that it can significantly reduce the risk of severe outcomes after infection.
