{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,26]],"date-time":"2026-09-26T15:19:24Z","timestamp":1790435964890,"version":"4.1.0"},"reference-count":67,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,12,11]],"date-time":"2021-12-11T00:00:00Z","timestamp":1639180800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000060","name":"National Institute of Allergy and Infectious Diseases","doi-asserted-by":"publisher","award":["Intramural Research Program"],"award-info":[{"award-number":["Intramural Research Program"]}],"id":[{"id":"10.13039\/100000060","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000038","name":"United States Food and Drug Administration","doi-asserted-by":"publisher","award":["institutional funds"],"award-info":[{"award-number":["institutional funds"]}],"id":[{"id":"10.13039\/100000038","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>The SARS-CoV-2 B.1.617 lineage variants, Kappa (B.1.617.1) and Delta (B.1.617.2, AY) emerged during the second wave of infections in India, but the Delta variants have become dominant worldwide and continue to evolve. Here, we compared B.1.617 variants for neutralization resistance by convalescent sera, mRNA vaccine-elicited sera, and therapeutic neutralizing antibodies using a pseudovirus neutralization assay. B.1.617.1, B.1.617.2, and AY.1 pseudoviruses showed a modest 1.5- to 4.4-fold reduction in neutralization by convalescent sera and vaccine-elicited sera. In comparison, similar modest reductions were also observed for C.37, P.1, R.1, and B.1.526 pseudoviruses, but 7- and 16-fold reductions for vaccine-elicited and convalescent sera, respectively, were seen for B.1.351 pseudoviruses. Among twenty-three therapeutic antibodies tested, four antibodies showed either complete or partial loss of neutralization against B.1.617.2 pseudoviruses and six antibodies showed either complete or partial loss of neutralization against B.1.617.1 and AY.1 pseudoviruses. Our results indicate that the current mRNA-based vaccines will likely remain effective in protecting against B.1.617 variants. Finally, the P681R substitution confers efficient cleavage of B.1.617 variants\u2019 spike proteins and the spike of Delta variants exhibited greater sensitivity to soluble ACE2 neutralization, as well as fusogenic activity, which may contribute to enhanced spread of Delta variants.<\/jats:p>","DOI":"10.3390\/v13122485","type":"journal-article","created":{"date-parts":[[2021,12,13]],"date-time":"2021-12-13T03:14:29Z","timestamp":1639365269000},"page":"2485","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":25,"title":["SARS-CoV-2 Delta Variant Displays Moderate Resistance to Neutralizing Antibodies and Spike Protein Properties of Higher Soluble ACE2 Sensitivity, Enhanced Cleavage and Fusogenic Activity"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1049-1929","authenticated-orcid":false,"given":"Sabari Nath","family":"Neerukonda","sequence":"first","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Russell","family":"Vassell","sequence":"additional","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1793-0450","authenticated-orcid":false,"given":"Sabrina","family":"Lusvarghi","sequence":"additional","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Richard","family":"Wang","sequence":"additional","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Fernando","family":"Echegaray","sequence":"additional","affiliation":[{"name":"Viral Epidemiology and Immunity Unit, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lisa","family":"Bentley","sequence":"additional","affiliation":[{"name":"Office of the Assistance Secretary for Preparedness and Response, U.S. Department of Health and Human Services, Washington, DC 20201, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ann E.","family":"Eakin","sequence":"additional","affiliation":[{"name":"Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Disease, National Institutes of Health, Rockville, MD 20892, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karl J.","family":"Erlandson","sequence":"additional","affiliation":[{"name":"Influenza and Emerging Infectious Diseases Division, Biomedical Advanced Research and Development Authority, U.S. Department of Health and Human Services, Washington, DC 20201, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Leah C.","family":"Katzelnick","sequence":"additional","affiliation":[{"name":"Viral Epidemiology and Immunity Unit, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9965-1289","authenticated-orcid":false,"given":"Carol D.","family":"Weiss","sequence":"additional","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wei","family":"Wang","sequence":"additional","affiliation":[{"name":"Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20903, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,12,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"403","DOI":"10.1056\/NEJMoa2035389","article-title":"Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine","volume":"384","author":"Baden","year":"2021","journal-title":"N. 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