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02.10.2021 | COVID-19 | Research article | Ausgabe 1/2021 Open Access

BMC Medicine 1/2021

Transmission event of SARS-CoV-2 delta variant reveals multiple vaccine breakthrough infections

BMC Medicine > Ausgabe 1/2021
Timothy Farinholt, Harsha Doddapaneni, Xiang Qin, Vipin Menon, Qingchang Meng, Ginger Metcalf, Hsu Chao, Marie-Claude Gingras, Vasanthi Avadhanula, Paige Farinholt, Charu Agrawal, Donna M. Muzny, Pedro A. Piedra, Richard A. Gibbs, Joseph Petrosino
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Supplementary Information

The online version contains supplementary material available at https://​doi.​org/​10.​1186/​s12916-021-02103-4.

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This study aims to identify the causative strain of SARS-CoV-2 in a cluster of vaccine breakthroughs. Vaccine breakthrough by a highly transmissible SARS-CoV-2 strain is a risk to global public health.


Nasopharyngeal swabs from suspected vaccine breakthrough cases were tested for SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) by qPCR (quantitative polymerase chain reaction) for Wuhan-Hu1 and alpha variant. Positive samples were then sequenced by Swift Normalase Amplicon Panels to determine the causal variant. GATK (genome analysis toolkit) variants were filtered with allele fraction ≥80 and min read depth 30x.


Viral sequencing revealed an infection cluster of 6 vaccinated patients infected with the delta (B.1.617.2) SARS-CoV-2 variant. With no history of vaccine breakthrough, this suggests the delta variant may possess immune evasion in patients that received the Pfizer BNT162b2, Moderna mRNA-1273, and Covaxin BBV152.


Delta variant may pose the highest risk out of any currently circulating SARS-CoV-2 variants, with previously described increased transmissibility over alpha variant and now, possible vaccine breakthrough.


Parts of this work was supported by the National Institute of Allergy and Infectious Diseases (1U19AI144297) and Baylor College of Medicine internal funding.
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