Int J Biol Sci 2022; 18(2):889-900. doi:10.7150/ijbs.68973 This issue


A systematic review of Vaccine Breakthrough Infections by SARS-CoV-2 Delta Variant

Mengxin Zhang1, Ying Liang1#, Dongsheng Yu2#, Bang Du1, Weyland Cheng1, Lifeng Li1, Zhidan Yu1, Shuying Luo1, Yaodong Zhang1, Huanmin Wang1, Xianwei Zhang1✉, Wancun Zhang1✉

1. Henan Key Laboratory of Children's Genetics and Metabolic Diseases, Children's Hospital Affiliated to Zhengzhou University, Henan Children's Hospital, Zhengzhou Children's Hospital, Zhengzhou 450018, China
2. Department of Chinese Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, 450000, China
# These authors contributed equally to this work.

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Zhang M, Liang Y, Yu D, Du B, Cheng W, Li L, Yu Z, Luo S, Zhang Y, Wang H, Zhang X, Zhang W. A systematic review of Vaccine Breakthrough Infections by SARS-CoV-2 Delta Variant. Int J Biol Sci 2022; 18(2):889-900. doi:10.7150/ijbs.68973. Available from

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Graphic abstract

Vaccines are proving to be highly effective in controlling hospitalization and deaths associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as shown by clinical trials and real-world evidence. However, a deadly second wave of coronavirus disease 2019 (COVID-19), infected by SARS-CoV-2 variants, especially the Delta (B.1.617.2) variant, with an increased number of post-vaccination breakthrough infections were reported in the world recently. Actually, Delta variant not only resulted in a severe surge of vaccine breakthrough infections which was accompanied with high viral load and transmissibility, but also challenged the development of effective vaccines. Therefore, the biological characteristics and epidemiological profile of Delta variant, the current status of Delta variant vaccine breakthrough infections and the mechanism of vaccine breakthrough infections were discussed in this article. In addition, the significant role of the Delta variant spike (S) protein in the mechanism of immune escape of SARS-CoV-2 was highlighted in this article. In particular, we further discussed key points on the future SARS-CoV-2 vaccine research and development, hoping to make a contribution to the early, accurate and rapid control of the COVID-19 epidemic.

Keywords: SARS-CoV-2, COVID-19, Delta variant, Vaccine, Breakthrough infection, S protein