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.
【저자키워드】 COVID-19, coronavirus disease, severe acute respiratory syndrome coronavirus 2, viruses, respiratory infections, SARS-CoV-2, coronavirus, SARS, Contact tracing, delta variant, secondary attack rate, Spain, Omicron variant, vaccine effectiveness, zoonoses., 【초록키워드】 zoonoses, Vaccine, vaccination, cross-sectional, SARS-COV-2 infection, variant, Infection, Delta, omicron, Spread, Probability, symptomatic, household contact, Odds ratio, risk of infection, severe disease, Contact, acute respiratory syndrome, 95% CI, index cases, performed, long-lasting, 【제목키워드】 Delta, omicron, household, replacement, attack, secondary, Rate,