Two distinct lineages of H1N1 influenza A viruses were antigenically similar until 1994, when new variants with significant antigenic differences emerged in China.
The deletion of the amino acid K at position 134 in these new variants, like A/Beijing/262/95, provided a selective advantage, leading to the dominance of the Chinese deletion lineage.
Research using reverse genetics confirmed that this specific K134 deletion was mainly responsible for the antigenic changes, highlighting the importance of a compatible neuraminidase surface protein for effective viral growth.