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Volume 28, Number 10—October 2022

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 Pérez-Quílez, Amaia Castillo-Zuza, Elisa Martró, Antoni E. Bordoy, Verónica Saludes, Ignacio Blanco, Laura Soldevila, Oriol Estrada, Lluís Valerio, Sílvia Roure, and Xavier VallèsComments to Author 
Author affiliations: North Metropolitan International Health Program, Catalan Institute of Health (PROSICS), Badalona, Spain (I. López-Muñoz, A. Torrella, O. Pérez-Quílez, A. Castillo-Zuza, L. Soldevila, L. Valerio, S. Roure, X. Vallès); Hospital Universitari Germans Trias i Pujol, Badalona (E. Martró, A.E. Bordoy, V. Saludes, I. Blanco, L. Soldevila, S. Roure); Center for Biomedical Research in Epidemiology and Public Health (CIBEREPS), Instituto de Salud Carlos III, Madrid, Spain (E. Martró, A.E. Bordoy, V. Saludes); Institut d’Investigació en Ciències de la Salut Germans Trias i Pujol, Badalona (E. Martró, A.E. Bordoy, V. Saludes, I. Blanco, O. Estrada, X. Vallès); Fundació Lluita contra la Sida i les Malalties Transmissibles, Badalona (L. Soldevila, S. Roure, X. Vallès)

Main Article

Table 3

Risk of infection among contacts relative to vaccination status in a study of SARS-CoV-2 secondary attack rates in vaccinated and unvaccinated household contacts during replacement of Delta with Omicron variant, Spain*

Variable Delta-dominant period
Omicron-dominant period
RR§ (95% CI) p value
Patients† p value‡ Patients† p value‡
Vaccination status, contacts
Vaccinated 50/101 (49.5) 0.1 112/124 (90.3) 0.3 6.48 (3.0–13.8) <0.001
Unvaccinated 35/56 (62.5) 28/29 (96.6) 10.4 (1.2–82.5) 0.03
Vaccinated, <20 wk 23/62 (37.1) 0.002

59/65 (90.8) 0.8
9.16 (3.4–25.0) <0.001
Vaccinated, >20 wk
27/39 (69.3)
52/58 (89.7)
2.91 (0.8–10.2)
Vaccination status, index
Vaccinated 67/112 (59.8) 0.02 108/120 (90.0) 0.2 3.99 (2.0–8.1) <0.001
Unvaccinated 18/45 (40.0) 32/33 (97.0) 43.5 (5.1–369.9) 0.001

*RR, relative risk †Values are no. infected/total no. (%) patients in each strata. ‡p values for differences between vaccinated and unvaccinated groups. §RR between Omicron vs. Delta variant, adjusted by age of contact.

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Page created: August 11, 2022
Page updated: September 20, 2022
Page reviewed: September 20, 2022
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