Figure 1. Dominance of infection with SARS-CoV-2 Delta and Omicron variants in a study of secondary attack rates in vaccinated and unvaccinated household contacts, Spain. The study population was located in the northern part of the greater metropolitan area of Barcelona, Spain. Genotyping of 1,554 samples from patients with SARS-CoV-2 infections was conducted during November 23, 2020–February 8, 2021 to identify the dominant variant infecting the population. The cutoff date between the Delta and Omicron predominance periods was December 21, 2021.