Statistical analysis
ADVERSE EVENT
The sample size calculation was based on the assumption that heterologous booster immunization with Ad5-nCoV after three-dose priming with inactivated SARS-CoV-2 vaccine would elicit non-inferior and superior concentrations of neutralizing antibodies compared with a homologous booster dose with inactivated SARS-CoV-2 vaccine. We assumed that the one-sided α of inspection level was 0.025, the ratio of Ad5-nCoV group to inactivated SARS-CoV-2 vaccine group was 1:1, the non-inferiority limit of the GMT ratio was 0.67 (after 10 is the bottom log = −0.174), and the actual GMT ratio of the two groups was 2; thus, the study needed to recruit 80 participants in each group to achieve 99.86% power. When the sample size of each group was 80, the superiority of the GMT level of the Ad5-nCoV group was greater than that of the inactivated SARS-CoV-2 vaccine group, and the estimated power of the test was 88.16%, which met the test requirements. Thus, we decided on a total sample size of 200, with 100 for each group after adjusting for an attrition rate of 20% due to loss to follow-up. Power Analysis and Sample Size software (LLC, USA version 11.0.7) was used in these calculations.Sex, age, BMI, and other clinical characteristics were collected for each vaccine recipient. We used the medians and interquartile ranges (IQR) for age and time interval, and numbers (percentages) for categorical variables. All participants who received the booster dose were included in the safety population (Safety set [SS]). Safety data are presented as counts and percentages of participants with at least one solicited (local or systemic) adverse event. The analysis was based on the intention-to-treat cohort and calculated with chi-squared test or Fisher’s exact test. The immunogenicity objectives are reported based on the per-protocol set (PPS), and missing data were not imputed. Participants experienced no major protocol violations; complied with all inclusion criteria/exclusion criteria; completed the vaccinations within the time window, as required in the protocol; and completed all blood samplings. Levels of antibodies against SARS-CoV-2 are presented as the GMC/GMT, seroconversion/seropositive rate, and GMFI with 95% CI. The 95% CI was calculated based on the t-distribution of the log-transformed values back-transformed to the original scale. We used Student’s 