‘Mass use of antigen tests may promote the spread of undetectable viral variants’

Rome, March 29 (beraking latest news Health) – Sars-cov-2 N gene variants may impair the ability to use antigen tests for both diagnosis and mass testing to control virus transmission. This is what emerges from the study ‘Emergence of genetic variants of the N Sars-cov-2 antigen’, conducted by the director of the Molecular Medicine Department of the University of Padua Andrea Crisanti, together with Stefano Toppo (Unipd), Annamaria Cattelan and Vito Cianci of the Hospital / University of Padua, and recently published on ‘medRxiv’.

Genetic variants of the coronavirus pose a major threat to vaccination efforts around the world, as they can increase the rate of transmission of the virus and confer the ability of the virus to escape vaccine-induced immunity, with knock-on effects, respectively. herd immunity threshold and vaccine efficacy. These variants concern the Spike protein encoded by the S gene involved in the entry of the virus into the host cells and the main target of vaccines. But they can affect – explain the researchers – the whole genome of the virus. In particular, one of the genes that has numerous variants, even slightly more than the others according to the latest estimates, is the one that codes for the ‘N’ protein of the virus which is responsible for the packaging of the genetic material of the virus and which is called, in fact, nucleoprotein.

In Italy, as in many European countries, antigen tests are gaining a lot of popularity thanks to their flexibility and ease of use and are increasingly used for mass investigations with the aim of decreasing the transmission of the virus in large communities. Since June last year, some Regions in Italy have progressively extended the mass use of the antigen test with the aim of progressively replacing the molecular swabs.

While conducting a diagnostic investigation it was found that some swab samples that were not positive in the antigen tests showed a high viral load in the Rt-Pcr tests. Sequencing analysis of viruses showing discordant results in molecular and antigenic tests revealed the presence of multiple destructive mutations in the structure of protein N (the viral protein used to detect the presence of the virus in antigenic tests) clustered from position 229 to 374. , a region known to contain key areas that allow virus identification in these tests. A relevant fraction of the undetectable variants in the antigen test contained A376t mutations coupled to M241i.

“Further laboratory tests have also shown that this problem is common to antigenic tests developed by different manufacturers – explains Crisanti – The sequences of viruses with these mutations are much more frequent in samples negative for antigen tests but with positive Pcr and are progressively increased by frequency over time in Veneto, a region that has significantly increased the use of antigenic tests, reaching almost 68% of the total. It is therefore assumed – concludes Crisanti – that the mass use of rapid antigenic tests may unintentionally favor the spread of variants viral not detectable by these tests, thus contributing to their free circulation and the ineffectiveness of their containment “.