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Update: Influenza Activity -- Worldwide and Recommendations for Influenza Vaccine Composition for the 1990-91 Influenza Season

Worldwide

During the 1989-90 influenza season, influenza type A(H3N2) viruses have caused most influenza activity worldwide. Influenza B has been isolated in 19 countries; isolates of influenza A(H1N1) have been uncommon.

In the 1989-90 season, influenza A(H3N2) activity began earlier than usual in the northern hemisphere. In Asia, Europe, and North America, outbreaks occurred as early as October and November. From October 1989 through March 1990, epidemics or local outbreaks of influenza A(H3N2) were reported in 21 countries: Belgium, Bulgaria, Canada, China, Czechoslovakia, Federal Republic of Germany, Finland, France, Greece, Iran, Israel, Italy, Japan, Netherlands, Republic of Korea, Spain, Sweden, Switzerland, United Kingdom, United States, and Union of Soviet Socialist Republics (USSR). Six countries reported sporadic* isolates of influenza A(H3N2): Austria, Denmark, Egypt, German Democratic Republic, Norway, and Yugoslavia.

Influenza B has been isolated from outbreaks in Finland, France, Italy, and Japan. Sporadic cases occurred in 15 countries: Australia, Canada, China, Denmark, Federal Republic of Germany, Hong Kong, Hungary, Israel, Norway, Sweden, Switzerland, United Kingdom, United States, USSR, and Yugoslavia.

Influenza A(H1N1) has been isolated from sporadic cases in Canada, France, the United States, and Yugoslavia. Both influenza A(H3N2) and A(H1N1) viruses were isolated from an outbreak reported in the United States. Antigenic Analysis of Recent Influenza Isolates and Recommendations for Influenza Vaccine Composition for the 1990-91 Season

Three antigenically distinct groups of influenza A(H3N2) viruses were isolated worldwide this season; most were A/Shanghai/11/87- and A/England/427/88-like (Table 1). Influenza A(H1N1) isolates and influenza B isolates studied were similar to those used in the vaccine for the 1989-90 season. After considering data on these and other virus isolates, the World Health Organization (WHO) recommended that the trivalent influenza vaccine for the 1990-91 season contain type A(H3N2) A/Guizhou/54/89-like antigen and retain the type A(H1N1) (A/Singapore/6/86-like) and type B (B/Yamagata/16/88-like) components of the 1989-90 vaccine (1).

Antigenic analysis of influenza A(H3N2) viruses isolated worldwide indicates that most of these viruses were A/Shanghai/11/87- and A/England/427/88-like. The most prevalent group of viruses resembles the majority of viruses isolated during the 1988-89 influenza season and are similar to the H3N2 component of this year's vaccine (1,2).

The second group of influenza A(H3N2) viruses that were antigenically distinguishable from the A/Shanghai/11/87-like viruses are represented by A/Guizhou/54/89 and A/Shanghai/16/89. Viruses in this group react poorly with antiserum to the 1989-90 vaccine strain (A/Shanghai/11/87); however, antiserum prepared to these viruses reacted well with A/Shanghai/11/87-like viruses from the 1989-90 season. Viruses antigenically similar to the A/Guizhou/54/89 and A/Shanghai/16/89 viruses were isolated in China, Europe, and the Americas. Persons vaccinated with A/Shanghai/11/87 vaccine had lower antibody responses to the A/Guizhou/54/89-like strains than to the vaccine strain. The postvaccine geometric mean titer for the A/Guizhou/54/89-like viruses was only 50% of that for the A/Shanghai/11/87 virus (Table 2).

The third group of influenza A(H3N2) viruses is represented by the A/Beijing/353/89 virus (Table 1). This virus also reacted poorly with antiserum to the 1989-90 vaccine strain, but, in contrast to viruses in the first group, did not produce ferret antiserum that reacted well with the majority of viruses from the current season. A/Beijing/353/89-like viruses have been isolated only from northern China and the United States; antibody response to this strain in persons receiving the A/Shanghai/11/87 vaccine was not reduced compared to the vaccine strain (1).

Antigenic analysis of the limited number of type A(H1N1) virus isolates indicates that, although some heterogeneity was detected among recent isolates, all reacted well with ferret antiserum prepared to the A/Taiwan/1/86 (A/Singapore/6/86-like) vaccine strain. The antibody induced in human volunteers by this vaccine component reacted well with recent representative A(H1N1) isolates.

Both influenza B/Victoria/2/87- and B/Yamagata/16/88-like viruses have been isolated this season in Asia, North America, and Europe. Some antigenic heterogeneity among the B/Yamagata/16/88-like viruses, such as that represented by B/Hong Kong/22/89, was detected (Table 3). Antibody induced by the B/Yamagata/16/88 virus in adult volunteers was broadly reactive against recent influenza B isolates, including the B/Hong Kong/22/89-like viruses (1).

The WHO recommendation for the 1990-91 influenza vaccine has been ratified by the Food and Drug Administration's Vaccine Advisory Panel. The specific antigens that will be in the 1990-91 vaccine for the United States are A/Shanghai/16/89(H3N2), A/Taiwan/1/86(H1N1), and B/Yamagata/16/89. Reported by: P Palmer, K Edwards, MD, Vanderbilt Univ, Nashville, Tennessee. F Ruben, MD, Univ of Pittsburgh, Pittsburgh, Pennsylvania. P Graves, G Meiklejohn, MD, Univ of Colorado, Denver, Colorado. G Schild, PhD, National Institute of Biological Standards and Control, London, United Kingdom. National Influenza Centers, Microbiology and Immunology Support Svcs, World Health Organization, Geneva, Switzerland. Div of Virology, Center for Biologics Evaluation and Research, Food and Drug Administration. Participating state and territorial health department epidemiologists and state public health laboratory directors. WHO Collaborating Center for Influenza, Influenza Br and Epidemiology Office, Div of Viral and Rickettsial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Because 6 months are required for production, quality control, and distribution of the approximately 30 million doses of influenza vaccine produced annually in the United States, vaccine strains must be selected by late March to early April each year. In 1990, three antigenically indistinguishable viruses (A/Guizhou/54/89, A/Shanghai/16/89, and A/Guandong/39/89)--all isolated in the People's Republic of China from June to September 1989--were candidates for the influenza A(H3N2) vaccine component. Because the growth properties of the A/Shanghai/16/89 virus were most favorable for vaccine production, this strain will be included in the 1990-91 influenza vaccine. This strain is antigenically distinct and should not be confused with the A/Shanghai/11/87(H3N2) virus included in last year's vaccine (Table 1). Specific recommendations by the Immunization Practices Advisory Committee for the prevention and control of influenza are forthcoming (3).

References

  1. World Health Organization. Recommended composition of influenza virus vaccines for use in the 1990-1991 season. Wkly Epidemiol Rec 1990;65:53-6.

  2. CDC. Update: influenza--United States, 1989-90. MMWR 1990;39:157-9.

  3. ACIP. Prevention and control of influenza: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1990 (in press).

*Sporadic activity is defined as sporadically occurring influenza-like illness or culture-confirmed influenza, with no outbreaks detected.

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