This
results
into
a
myriad
of
variants
that
are
unrecognised
by
the
antibodies
produced
in
previous
infection.
One
therefore
suffers
innumerable
cases
of
influenza.
Also,
this
phenomenon
prevents
the
development
of
an
effective
vaccine.
The
nomenclature
for
influenza
viruses
is
derived
from
the
changing
antigenic
pattern.
Virologists
name
the
viruses
according
to
their
type
(A,
B
or
C),
the
animal
of
origin
if
other
than
humans,
the
location
of
first
isolation,
the
strain
number,
and
the
year
of
isolation.
