Fluorescence corresponding to the Alpha variant could be detected , as this variant also harbors S : Δ69/70 . However , the fluorescence plateau values detected were considerably lower compared to those of Omicron . In addition , since Alpha has been completely displaced by Delta , the presence of the former variant in the monitored wastewater is unexpected . It should be also highlighted that the data obtained from the National Genomic Surveillance Network regarding the SARS - CoV-2 variants that circulated during each period were critical for the interpretation of the RT - PCR findings . This is based on the fact that the developed assay aims at a specific viral genomic target . In our case , up to 16 December 2021 , the vast majority of the genomic sequences that were characterized from Thessaloniki belonged to the Delta variant ( 92.8 % , i.e. , 1059 out of 1141 clinical samples that underwent typing ) ( National Public Health Organization - Greece ( EODY ) , 2021c ) and this assisted in drawing safe conclusions about the performance of our wastewater monitoring methodology .