TY - JOUR AU - López-Muñoz, Israel AU - Torrella, Ariadna AU - Pérez-Quílez, Olga AU - Castillo-Zuza, Amaia AU - Martró, Elisa AU - Bordoy, Antoni AU - Saludes, Verónica AU - Blanco, Ignacio AU - Soldevila, Laura AU - Estrada, Oriol AU - Valerio, Lluís AU - Roure, Sílvia AU - Vallès, Xavier T1 - SARS-CoV-2 Secondary Attack Rates in Vaccinated and Unvaccinated Household Contacts during Replacement of Delta with Omicron Variant, Spain T2 - Emerging Infectious Disease journal PY - 2022 VL - 28 IS - 10 SP - 1999 SN - 1080-6059 AB - 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. KW - COVID-19 KW - respiratory infections KW - severe acute respiratory syndrome coronavirus 2 KW - SARS-CoV-2 KW - SARS KW - coronavirus disease KW - zoonoses KW - viruses KW - coronavirus KW - contact tracing KW - vaccine effectiveness KW - Delta variant KW - Omicron variant KW - secondary attack rate KW - Spain DO - 10.3201/eid2810.220494 UR - https://wwwnc.cdc.gov/eid/article/28/10/22-0494_article ER - End of Reference