Objective:To analyze the clinical characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine breakthrough infections in children, and to provide reference basis for the SARS-CoV-2 vaccination in children.Methods:A total of 97 children aged 3 to 14 years and diagnosed with coronavirus disease 2019 (COVID-19) admitted to Xi′an People′s Hospital (Xi′an Fourth Hospital) from December 27, 2021 to February 7, 2022 were included. According to the COVID-19 vaccination status, the enrolled children were divided into unvaccinated group, partially vaccinated group and fully vaccinated group, and the clinical data of the children in the three groups were collected and compared. Chi-square test, two independent sample t-test and Kruskal-Wallis H test were used for statistical analysis. Results:Totally 97 children including 49 males and 48 females were enrolled, with 87(89.7%) children of mild type, 10(10.3%) children of common type, and no severe or critical case. The proportions of unvaccinated, partially vaccinated and fully vaccinated preschool-aged children (3 to 6 years old) were 56.5%(13/23), 30.8%(12/39) and 17.1%(6/35), respectively, while those of school-aged children (7 to 14 years old) were 43.5%(10/23), 69.2%(27/39) and 82.9%(29/35), respectively. The vaccination proportion in preschool-aged children was significantly lower than that in school-age children ( χ2=9.94, P=0.007). The proportion of the children with fever in fully vaccinated group was 17.1%(6/35), which was lower than that in unvaccinated group (43.5%, 10/23), and the difference was statistically significant ( χ2=4.82, P=0.028). The cycle threshold (Ct) values of the open reading frame ( ORF)1 ab gene in the unvaccinated, partially vaccinated and fully vaccinated groups were 33.77(26.87, 36.58), 35.23 (33.45, 38.57) and 37.12 (34.91, 39.39), respectively, and there was a statistically significant difference among the groups ( H=7.76, P=0.021). The Ct values of the nucleocapsid protein ( N) gene in the three groups were 32.26(25.85, 36.18), 35.12(33.18, 37.96) and 37.26(34.27, 39.24), respectively, and the difference among the groups was statistically significant ( H=7.84, P=0.020). The Ct values of ORF1 ab gene and N gene in fully vaccinated group were higher than those in unvaccinated group, and the differences were statistically significant ( Z=-2.69, P=0.007 and Z=-2.39, P=0.017, respectively). The duration of viral shedding in fully vaccinated children was (9.9±4.1) d, which was shorter than that in unvaccinated children ((12.8±3.7) d), and the difference was statistically significant ( t=2.72, P=0.009). Conclusions:The majority of children with breakthrough infections with SARS-CoV-2 are mild. Vaccination may effectively shorten the duration of viral shedding. And fully vaccination is associated with mild clinical symptoms and lower serum viral load compared to unvaccinated children.