Lineage size breakdown of Poland genomes collected each month. Distribution of major nine SARS-Cov-2 lineages circulating in Poland between March 2020 and February 2021, estimated based on whole-genome sequencing. No data on the sequences collected in July and October 2020 were available. Displayed codes indicate virus variants based on PANGO classification. During the first month of analysis, the dominant virus variant was lineage B.1 (20A), with 27 cases observed in March 2020 (52.94%), and lasted during the entire period of sampling. In April and June 2020, variant B.1.1.29 (20A) dominated in 20 (27.03%) and 21 (51.22%) of sequenced isolates, respectively. In May, lineage B.1.213 (20A) appeared, which accounted for 40.32% (n = 25) of cases. In August and September, the most common virus type was B.1.1.227 (20B), at 66.67 (n = 3) and 36.36% (n = 4), respectively. In the next two months, the B.1.258 (20A) variant dominated (n = 30 (27.27%) for November and n = 47 (29.19%) in December). In January 2021, the main virus strain was B.1.221 (20A) (n = 115 (26.08%)). February showed the highest contribution of variant B.1.1.7 (20I/501Y.V1) with 79 cases (51.97%).