Circulation of Human Immunodeficiency Virus 1 A6 Variant in the Eastern Border of the European Union—Dynamics of the Virus Transmissions Between Poland and Ukraine

Background The human immunodeficiency virus (HIV) type 1 A6 variant is dominating in high-prevalence Eastern European countries, with increasing prevalence over the remaining regions of Europe. The recent war in Ukraine may contribute to further introductions of this A6 lineage. Our aim was to model the transmission dynamics of the HIV-1 A6 variant between Poland and Ukraine. Methods HIV-1 A6 partial pol sequences originating from Poland (n = 1185) and Ukraine (n = 653) were combined with publicly available sequences (n = 7675) from 37 other countries. We used maximum likelihood-based tree estimation followed by a bayesian inference strategy to characterize the putative transmission clades. Asymmetric discrete phylogeographic analysis was used to identify the best-supported virus migration events across administrative regions of Poland and Ukraine. Results We identified 206 clades (n = 1362 sequences) circulating in Poland or Ukraine (63 binational clades, 79 exclusively Polish, and 64 exclusively Ukrainian). Cross-border migrations were almost exclusively unidirectional (from Ukraine to Poland, 99.4%), mainly from Eastern and Southern Ukraine (Donetsk, 49.7%; Odesa, 17.6% regions) to the Central (Masovian, 67.3%; Lodz, 18.2%) and West Pomeranian (10.1%) districts of Poland. The primary sources of viral dispersal were the Eastern regions of Ukraine, long affected by armed conflict, and large population centers in Poland. Conclusions The Polish outbreak of the A6 epidemic was fueled by complex viral migration patterns across the country, together with cross-border transmissions from Ukraine. There is an urgent need to include war-displaced people in the national HIV prevention and treatment programs to reduce the further spread of transmission networks.