tetano
Editor, Senior Moderator
Emerg Infect Dis
. 2022 Aug 29;28(10).
doi: 10.3201/eid2810.220494. Online ahead of print.
SARS-CoV-2 Secondary Attack Rates in Vaccinated and Unvaccinated Household Contacts during Replacement of Delta with Omicron Variant, Spain
Israel López-Muñoz, Ariadna Torrella, Olga López-Quílez, Amaia Castillo-Zuza, Elisa Martró, Antoni E Bordoy, Verónica Saludes, Ignacio Blanco, Laura Soldevila, Oriol Estrada, Lluís Valerio, Sílvia Roure, Xavier Vallès
Abstract
We performed a prospective, cross-sectional study of household contacts of symptomatic index case-patients with SARS-CoV-2 infection during the shift from Delta- to Omicron-dominant variants in Spain. We included 466 household contacts from 227 index cases. The secondary attack rate was 58.2% (95% CI 49.1%-62.6%) during the Delta-dominant period and 80.9% (95% CI 75.0%-86.9%) during the Omicron-dominant period. During the Delta-dominant period, unvaccinated contacts had higher probability of infection than vaccinated contacts (odds ratio 5.42, 95% CI 1.6-18.6), but this effect disappeared at ≈20 weeks after vaccination. Contacts showed a higher relative risk of infection (9.16, 95% CI 3.4-25.0) in the Omicron-dominant than Delta-dominant period when vaccinated within the previous 20 weeks. Our data suggest vaccine evasion might be a cause of rapid spread of the Omicron variant. We recommend a focus on developing vaccines with long-lasting protection against severe disease, rather than only against infectivity.
Keywords: COVID-19; Delta variant; Omicron variant; SARS; SARS-CoV-2; Spain; contact tracing; coronavirus; coronavirus disease; respiratory infections; secondary attack rate; severe acute respiratory syndrome coronavirus 2; vaccine effectiveness; viruses; zoonoses.
. 2022 Aug 29;28(10).
doi: 10.3201/eid2810.220494. Online ahead of print.
SARS-CoV-2 Secondary Attack Rates in Vaccinated and Unvaccinated Household Contacts during Replacement of Delta with Omicron Variant, Spain
Israel López-Muñoz, Ariadna Torrella, Olga López-Quílez, Amaia Castillo-Zuza, Elisa Martró, Antoni E Bordoy, Verónica Saludes, Ignacio Blanco, Laura Soldevila, Oriol Estrada, Lluís Valerio, Sílvia Roure, Xavier Vallès
- PMID: 36037811
- DOI: 10.3201/eid2810.220494
Abstract
We performed a prospective, cross-sectional study of household contacts of symptomatic index case-patients with SARS-CoV-2 infection during the shift from Delta- to Omicron-dominant variants in Spain. We included 466 household contacts from 227 index cases. The secondary attack rate was 58.2% (95% CI 49.1%-62.6%) during the Delta-dominant period and 80.9% (95% CI 75.0%-86.9%) during the Omicron-dominant period. During the Delta-dominant period, unvaccinated contacts had higher probability of infection than vaccinated contacts (odds ratio 5.42, 95% CI 1.6-18.6), but this effect disappeared at ≈20 weeks after vaccination. Contacts showed a higher relative risk of infection (9.16, 95% CI 3.4-25.0) in the Omicron-dominant than Delta-dominant period when vaccinated within the previous 20 weeks. Our data suggest vaccine evasion might be a cause of rapid spread of the Omicron variant. We recommend a focus on developing vaccines with long-lasting protection against severe disease, rather than only against infectivity.
Keywords: COVID-19; Delta variant; Omicron variant; SARS; SARS-CoV-2; Spain; contact tracing; coronavirus; coronavirus disease; respiratory infections; secondary attack rate; severe acute respiratory syndrome coronavirus 2; vaccine effectiveness; viruses; zoonoses.