What type of mutation leads to changes in surface proteins like HA and NA in viruses?

Antigenic drift is the process through which small, gradual changes occur in the surface proteins of viruses, such as hemagglutinin (HA) and neuraminidase (NA). These proteins are important for the virus's ability to evade the immune system, as the immune responses generated by a previous infection or vaccination may be less effective against the altered forms of these proteins.

During antigenic drift, point mutations — which are small changes in the nucleotide sequence of the virus's genome — accumulate over time as the virus replicates. This accumulation of mutations can change the amino acid sequences of surface proteins, leading to variations that may help the virus escape immune detection. This gradual evolution is particularly common in RNA viruses, like influenza, due to their higher mutation rates.

In contrast, antigenic shift involves a more dramatic change, often through the reassortment of genomic segments between different viral strains, which can lead to the emergence of significantly different surface antigens. Although point mutations and substitution mutations can describe specific changes at the nucleotide or amino acid level, it is the concept of antigenic drift that encapsulates the ongoing process of slight, accumulating changes in viral surface proteins that help explain how viruses can continually adapt and evade the host's immune response