Tracking HIV A6 strain in Europe: implications for injectable CAB-LA for treatment or PrEP

Simon Collins, HIV i-Base

A phylogenetic and modeling study about the spread of the A6 strain of HIV in Europe has been published in CID together with an editorial looking at the clinical implications for using injectable cabotegravir as treatment or prevention.

Earlier research reported that A6 is associated with a lower barrier to developing cabotegravir resistance and a higher risk of treatment failure, even in the context of perfect adherence to two-monthly injections.

Other factors identified in the low number of treatment failures, include baseline resistance to rilpivirine, low drug levels of rilpivirine, BMI >30 (perhaps linked to lower drug levels), and the L74I integrase mutation (when other factors are present).

A6 was previously reported as circulating in Russia and Ukraine but the migration due to the war against Ukraine has also been associated with new cases being identified in Poland, and likely other European countries.

The accompanying editorial notes that CAB-LA failure rates are low, but this risk increases when several of the above risk factors are present.

Having the A6 strain as the only risk, doesn’t prevent effective use of CAB-LA, so management can be individualised. perhaps with closer monitoring. Use would not be recommended though if A6 is presents together with other factors associated with treatment failure.


  1. Serwin K et al. Circulation of HIV-1 A6 variant in the eastern border of the European Union—dynamics of the virus transmissions between Poland and Ukraine. Clinical Infectious Diseases, 76(10):1716–1724. (15 May 2023).
  2. Jonathan M Schapiro, Dynamics of Human Immunodeficiency Virus Type 1 A6 Variant Transmissions Between Poland and Ukraine, Clinical Infectious Diseases, 76(10):1725–1726. (15 May 2023).

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