Current Trends Antigenic Analysis of Recent Influenza
Isolates
Influenza type A(H1N1) and type B viruses received at CDC thus
far
this winter from outbreaks and sporadic cases in the United States
have been closely related to the reference strains
A/England/333/80(H1N1) and B Singapore/222/79, respectively. Since
about July 1981, influenza type A(H3N2) viruses have been received
from Australia, Chile, Guam, Indonesia, Japan, People's Republic of
China, Taiwan Province of China, and Trinidad and Tobago. As in
the
preceding year, the isolates have exhibited heterogeneous reaction
patterns in hemagglutination-inhibition tests with ferret serum
specimens. Varying proportions of the viruses from different
locations are more closely related to A/Texas/1/77 or
A/Bangkok/1/79.
A minority of recent isolates have been found to exhibit some
further
antigenic drift from earlier strains and to resemble the virus
A/Shanghai/31/80 isolated in December 1980 from a sporadic case of
influenza. As shown in Table 1, A/Shanghai/31/80 exhibits an
asymmetric antigenic difference from A/Bangkok/1/79, in that
antiserum
to A/Bangkok/1/79 usually inhibits the variant to a titer 4-fold
lower
than homologous, whereas antiserum to A/Shanghai/31/80 reacts
almost
equivalently with itself and with A/Bangkok/1/79. A further
characteristic of A/Shanghai/31/80-like viruses is their low
inhibition by A/Texas/1/77 and A/Bangkok/2/79 antisera. The
above-described variants have been isolated concurrently, and there
is
no clear evidence of A/Shanghai/31/80-like viruses, for example,
achieving predominance and being responsible for major outbreaks or
epidemics in Asia or elsewhere. Prevalence of antibody to
A/Bangkok/1/79 and A/Shanghai/31/80 appears similar in the general
population in the United States and the United Kingdom, where this
has
been studied by the WHO Collaborating Centers for Influenza.
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