|
Contents
|
|
Strains are characterised antigenically to allow selection
of an appropriate vaccine strain. Strains are characterised biochemically,
usually by genome (nucleic acid) sequencing, to identify epidemiological
relationships between field strains.
It is important to recognise that at the present time nucleotide sequence
analysis cannot be used to determine vaccine strain selection as
• strains with very similar nucleotide sequences can be antigenically
very diverse and
• strains with very different nucleotide sequences can be antigenically
similar.
These observations arise because
• for molecular epidemiology it is usual only to sequence a small region
of the genome (100-200 nucleotides), whereas the antigenicity of the virus
results from interactions between many separate regions of the genome.
• only very small differences in sequence at critical sites can have major
effects on antigenicity.
It is not currently possible to predict antigenicity on the basis of nucleotide
sequence. Monoclonal antibodies (MAbs) bind to single, defined epitopes
and it is possible to associate defined nucleotide substitutions with
loss of binding of a particular MAb. It may ultimately be possible to
predict changes in nucleotide sequence based on patterns of MAb binding
and vice versa.
|
