# Two clade 2.3.4.4b H5N1 viruses formed reassortants with human influenza A in vitro: 20 of 2,698 clones

- Published: 2026-11-11 08:20 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: H5N1 clade 2.3.4.4b, influenza A reassortment, human H1N1, human H3N2, plaque-purified clones, polymerase activity, PA and PB2 subunits, avian influenza
- URL: https://realtech.media/news/rt-c39b36e81529a787d95adf73_two_clade_2/

**In cell culture, reassortants formed with human H1N1 and H3N2 viruses, but rarely. Polymerase compatibility alone does not appear to explain their recovery.**

![Two clade 2.3.4.4b H5N1 viruses formed reassortants with human influenza A in vitro: 20 of 2,698 clones](https://realtech.media/media/2026/11/eaa0608734213f3b.jpg)
*Airman 1st Class Cody Dowell, Wikimedia Commons, Public domain*

Researchers reported in Proceedings of the National Academy of Sciences that two contemporary clade 2.3.4.4b H5N1 viruses can exchange genome segments with human-adapted influenza A viruses (IAV) in cell culture [1]. They used a biosafe reassortment system and coinfected cells with human H1N1 and H3N2 viruses under several conditions.

The authors genotyped 2,698 plaque-purified viral clones and recovered 20 reassortants, or 0.74% [1].

Polymerase assays showed that some human IAV subunits, particularly H1N1 PA or H3N2 PB2, increased H5N1 polymerase activity [1]. The authors conclude that factors beyond polymerase compatibility may limit recovery of reassortants [1]. All experiments were performed in vitro.

## Sources

1. [Proceedings of the National Academy of Sciences](https://doi.org/10.1073/pnas.2631654123)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-c39b36e81529a787d95adf73_two_clade_2/