Vaccine breakthrough is a phenomenon wherein vaccinated individuals become infected with disease despite adequate protection. During this study period, the Centers for Disease Control (CDC) reported 66.6% of US people have been fully vaccinated. Any measures to improve trust would increase vaccination rates. This study aims to understand vaccine breakthrough cases in COVID-19 by comparing their severity to unvaccinated cases. Our objective is to compare disease severity based on the worst initial vital signs (temperature, respiratory rate, oxygen saturation), length of stay (LOS), and age between vaccinated and unvaccinated COVID-19 cases.
We conducted a retrospective cohort study at Berkshire Medical Center between July 15, 2021, through October 31, 2021. IRB exemption was obtained. Patient records were reviewed for vaccination status, age, vital signs, and LOS. We used forward and backward logistic regressions to determine significant variables and odds ratios to quantify the association between them. We then computed two-sample t-tests to compare the variables between vaccinated and unvaccinated groups.
There were 151 vaccinated and 141 unvaccinated COVID-19 cases. Using a forward logistic regression model, we found significant associations between vaccination status, age (p<0.005), and max Temp (p<0.005). Using a backward logistic regression model, we found significant associations between vaccination status, age (p<0.005), max Temp (p<0.005), and min SpO2 (p<0.031). Odds ratios were 1.0725 (age), 0.6608 (max Temp), and 1.0873 (min SpO2). Two-sample t-tests showed significant differences in age and max Temp between vaccinated and unvaccinated groups while no significant differences were found in LOS, max RR, and min SpO2.
Our results suggest that vaccination may lead to milder disease even against virulent strains such as the Delta variant. These findings were similar to another study during the Alpha variant peak that demonstrated that vaccinated patients had less disease severity. Vaccination was associated with a 7.25% higher likelihood of being older, a 66.08% lower likelihood of having a higher temperature, and an 8.73% higher likelihood of having lower SpO2. There were significant differences in age and max Temp between vaccinated and unvaccinated groups indicating that vaccination may be associated with less disease severity even in an older population.
Thai D, Sarcia N, Bodine AM. Disease Severity in COVID-19 Breakthrough Cases. Advances in Clinical Medical Research and Healthcare Delivery. 2022; 2(2). doi: 10.53785/2769-2779.1095.