Testing Pandemic trH3N2 Vaccine
August 3, 2011
The CDC has
released sequences (at
GISAID) of new constructs, A/Minnesota/11/2010 X-203 and
X-203A, indicating these isolates are undergoing testing as pandemic
vaccine target. The first human case of trH3N2 in the United States
was reported in late 2009. There have been eight additional cases in
2011, and sequence
analysis raises concerns that these isolates are transmitting in
humans. Several internal genes are virtually identical, including
E618D, and there are similarities
in the external genes.
The viruses are triple reassortants with human H3, N2, and PB1.
these genes trace back to the 1990’s when a swine infected with
was infected with a human H3N2 virus creating double
reassortants. In the
late 1990's an avian infection of a swine infected with a double
created a triple reassortant with a polymerase complex composed of
and avian PB2 and PA.
The triple reassortants with human H3 and N2 are designated trH3N2, but
and N2 have evolved significantly in swine, severely compromising the
to seasonal H3N2 as well as the H3N2 vaccine. Consequently, one
human trH3N2 isolates from Minnesota
is the target of this new vaccine. The decision to make this
this time raises concerns that unreported and unpublished infections
further supported human to human transmission.
The sequences released today also indicate new vaccines are being
H1N1, as well as seasonal H3N2 and influenza B, even though the recommendation
to WHO and the FDA
was to leave
targets unchanged fro the 2011/2012 flu season in the northern
Consequently, worldwide vaccine production is targeting isolates from
earlier, which appear to be no
Detail on the reasons behind the emphasis on new vaccine targets at
would be useful.
at Nature Precedings