| Summary: | <h4>Background</h4> <p>While HIV‐1 subtype B has caused a large epidemic in the western world, its transmission in Ukraine remains poorly understood. We assessed the genetic diversity of HIV‐1 subtype B viruses circulating in Ukraine, characterized transmission group structure, and estimated key evolutionary and epidemiological parameters.</p> <h4>Methods</h4> <p>We analysed 120 HIV‐1 subtype B pol sequences (including 46 newly generated) sampled from patients residing in 11 regions of Ukraine between 2002‐2017. Phylogenies were estimated using maximum likelihood and Bayesian phylogenetic methods. A Bayesian molecular clock coalescent analysis was used to estimate effective population size dynamics and to date the most recent common ancestors of identified clades. A phylodynamic birth‐death model was used to estimate the effective reproductive number (Re) of these clades.</p> <h4>Results</h4> <p>We identified two phylogenetically distinct predominantly Ukrainian (≥75%) clades of HIV‐1 subtype B. We found no significant transmission group structure for either clade, suggesting frequent mixing among transmission groups. The estimated dates of origin of both subtype B clades were around early 1970s, similar to the introduction of HIV‐1 subtype A into Ukraine. Re for Clade 1 was estimated to be 1.42 (95% HPD 1.26‐1.56) and 1.69 (95% HPD 1.49‐1.84) for Clade 2.</p> <h4>Discussion</h4> <p>The subtype B epidemic in the country is no longer concentrated in specific geographical regions or transmission groups. The study results highlight the necessity for strengthening preventive and monitoring efforts to reduce the further spread of HIV‐1 subtype B.</p>
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