CD4 and COVID-19: In relation to the primary outcome of the study, changes of blood levels of CD4+T lymphocytes showed an increased from a mean of 910.7 (95% CI 741.9 to 1079.4) cells/μL at baseline to 1000.2 (95% CI 831.4 to 1168.9) after the second dose of COVID-19 vaccine in the group treated with the ABB C1® supplement, whereas, in the group treated with placebo, there was a decrease from 1055.1 (95% 867.0 to 1240.2) cells/μL at baseline to 929.8 (95% CI 743.1 to 1116.5) cells/μL (Figure 2).