In a study on infections among healthcare professionals, the authors found that "between 11 and 25 June 2021 (7-8 weeks after the second dose), 69 staff members tested positive for SARS-CoV-2. 62 participated in the study. Most were asymptomatic or mildly symptomatic and all recovered. 22 complete genome sequences were obtained; all were Delta variants and differed from contemporary viruses obtained from the community or from hospital patients admitted before epidemic. Viral loads deduced from Ct values were 251 times higher than in cases infected with the original strain in March / April 2020 ... "