Current Trends Antigenic Analysis of Recent Influenza
A(H1N1) Viruses
Laboratory tests with animal sera have demonstrated that
influenza
A(H1N1) viruses isolated from outbreaks in Southeast Asia and some
parts of Oceania from approximately March to August 1983 (1) have
undergone antigenic drift from the previously prevalent strains.
Post-infection ferret serum to A/Brazil/11/78, which reacted well
with
the A/England/333/80-like strains that had been preponderant among
H1N1 isolates during the past 2-3 years (2,3), reacts poorly with
most
recent isolates in hemagglutination inhibition (HI) tests. Ferret
antiserum to another variant, A/India/6263/80, which has
cocirculated
with A/England/333/80 (2,3), also reacts poorly with the recent
isolates.
When compared in reciprocal HI tests, the recent isolates are
heterogenous (Table 1). One type of reaction pattern is
exemplified
by the virus A/Chile/1/83, which is rather poorly inhibited by all
heterologous sera. The A/Chile/1/83 virus itself induces broadly
reactive antibodies when used to infect ferrets. Viruses with
similar
characteristics to A/Chile/1/83 have comprised the majority of
recently tested isolates from Singapore and Thailand. Viruses from
New Caledonia and New Zealand, however, have exhibited two
alternative
types of reaction patterns. Examples are shown with A/New
Caledonia/4/83 and A/Dunedin/7/83 (Table 1). When inoculated into
ferrets, each virus induces antibody that reacts more with itself
than
with other 1983 variants. Both A/New Caledonia/4/83- and
A/Dunedin/7/83-like variants have been found from within the same
outbreaks in New Caledonia and New Zealand. Preliminary tests in
man
show that vaccine containing A/Brazil/11/78 virus induces antibody
that inhibits the new H1N1 variants better than does post-infection
A/Brazil/11/78 ferret serum.
Reported by WHO Collaborating Center for Influenza, Influenza Br,
Div
of Viral Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: It is possible that the genetic difference between
the new variants from Oceania is very small and that the two
strains
shown represent minor variants in a common evolutionary path; this
would parallel a situation observed with some cocirculating
variants
of influenza A(H3N2), such as A/Bangkok/1/79 and A/Bangkok/2/79,
whose
hemagglutinin antigenic sites differ from each other by only two
amino
acids (4).
Continuing study of influenza A(H1N1) viruses from different
parts
of the world, including the Northern Hemisphere, is necessary to
determine whether any of the new variants will predominate.
Despite
the antigenic differences detected with highly specific,
post-infection ferret sera, it is likely that this year's vaccine,
which contains A/Brazil/11/78 as its H1N1 antigenic component,
would
be of benefit in protecting many people against the new virus
variants
if they spread in the United States, due to the broader antibody
response in man. Furthermore, H3N2 and type B viruses, which
continue
to circulate in the world, are also included in the vaccine.
References
CDC. Influenza--worldwide. MMWR 1983;32:502-4.
Cox NJ, Bai ZS, Kendal AP. Laboratory-based surveillance of
influenza A(H1N1) and A(H3N2) viruses in 1980-81: antigenic
and
genomic analyses. Bull WHO, 1983;143-52.
World Health Organization. Influenza in the world, October
1981-September 1982. WHO Wkly Epidem Rec 1982;50:389-93.
Both GW, Sleigh MS, Cox NJ, Kendal AP. H3 influenza
haemagglutinin from 1968-1980: multiple evolutionary path ways
and sequential amino acid changes at key antigenic sites. J
Virol
1983;48:52-60.
Disclaimer
All MMWR HTML documents published before January 1993 are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.
**Questions or messages regarding errors in formatting should be addressed to mmwrq@cdc.gov.
