Background
One of the fastest-growing HIV-1 epidemics is the A6 sub-subtype, which has dominated countries of the Former Soviet Union. In Poland, the HIV-1 A6 prevalence has been increasing for over a decade, boosted after 2022 by the extensive influx of individuals from Ukraine. Our goal was to assess the changes in phylogenetic clustering patterns and cluster growth of HIV A6 in Poland between 2020 and 2024
Methods
We created a dataset of 14,007 unique HIV-1 pol gene fragments of sub-subtype A6 from publicly available sequence databases and included 2,089 sequences from Poland sampled between 1996 and 2024. The dataset was divided into three data points: up to 2020, 2022, and 2024. We defined a cluster as a sample introduced into Poland, representing a local transmission chain with a distinct entry point. Time-calibration of the maximum-likelihood phylogenetic trees and discrete phylogeographic inference were performed to evaluate distinct clusters
Results
The number of A6 Polish clusters has increased from 74 in 2020 to 105 in 2022 and 191 in 2024. Median cluster sizes were 2 (2–306, n=628), 2 (2–457, n=939), and 2 (2–655, n=1499), respectively. These clusters comprised nearly all sequences from individuals born in Poland, with the proportion growing from 88.1% in 2020 to 90.5% in 2024. The fraction of females in clusters increased notably from 9.0% (n=28) in the 2020-2022 period to 19.6% (n=110; p<0.001) in the two following years, driven mainly by foreign-born women. The number of non-clustered (singleton) sequences increased significantly from 21.9% (n=87) to 35.5% (n=307; p<0.001), and the proportion of singletons surged from 70.5% in 2020 to 75.8% in 2024. The share of migrants among non-clustered sequences increased from 80.5% (n=70) in the first two years of the study to 90.2% (n=279; p<0.01) in the most recent two years. We noted a substantial rise in virus introductions into the country, with 120 cases in the period of two years before 2022 and 399 importations in the following two years
Conclusions
The number and size of A6 clusters in Poland have increased, including those involving female sequences. Several of the large male-dominated clusters continue to drive the spread of domestic infections and national A6 epidemic is propelled by infections from war related migration. Containing the growth and number of clusters presents a healthcare challenge, especially as resources are constrained by the need to support the large influx of individuals from abroad
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