T he mass vaccination against SARS-CoV-2 that began at the end of 2020 reduced COVID-19-related mortality and severity in countries where substantial vaccine coverage was achieved (1,2). The vaccines also had a protective effect against the most recent variants (3,4). However, expectations that vaccines would stop community transmission of SARS-CoV-2 through herd immunity were quickly dampened by the early observation of infection and re-infection among vaccinated persons; waning vaccine effectiveness against transmission (VET) over time was observed (1,3) and confirmed in a large systematic literature review (5). Despite these results, protective effects of vaccination against infection among contacts have been reported (6). The vaccination status of index case-patients was also shown to play a role (6), underscoring the importance of vaccination for reducing the circulation of SARS-CoV-2. Nonetheless, the emergence of new variants of concern (VOC) with increased infectivity is an ongoing challenge for VET of currently licensed vaccines; early reports have shown a substantially lower VET for the Delta variant (B.1.617.2) compared with previous VOCs (7). Furthermore, rapid replacement of the Delta variant by Omicron (B.1.1.529) began in late 2021; the Omicron variant showed a transmission advantage because of its shorter generation time (S. Abbott et al., unpub. data, https://www.medrxiv.org/content/10.1101/2 022.01.08.22268920v1).Evaluating both variant virulence and SARS-CoV-2 VET under high vaccine coverage levels has major epidemiologic, social, and policy implications. We report the results of an observational study of household contacts of SARS-CoV-2-infected index case-patients during a Delta variant-dominant period from September to December 2021 and an Omicron variant-dominant period during January 2022 in a north-metropolitan area of Barcelona, Spain. We
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.