Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Update on Influenza Activity -- Worldwide

Since the end of last winter's influenza season in the Northern Hemisphere, low levels of activity of influenza A/Taiwan/1/86(H1N1)-like strains (the predominant strain last winter) have been reported in Asia and Oceania. Similar strains have been reported from outbreaks in South Africa (Table 1). An isolated infection with influenza A(H1N1) was confirmed in the United Kingdom. In the Americas, A/Taiwan/1/86-like viruses have been reported from Uruguay and Chile -- the first reported spread of the 1986 A(H1N1) variant to South America following its circulation in North America.

Influenza B has been the most frequently isolated virus. In Oceania, localized outbreaks were reported in Australia and epidemic activity in New Zealand. In the Americas, influenza B was isolated from children in Guatemala during May, and localized influenza B activity was reported in Brazil during July and August. Influenza B infections were documented in the United States during summer and early fall. A child in Wisconsin became ill during June upon returning from the Philippines, where the infection was most likely acquired. Four cases were reported from Tucson, Arizona: one in July and three in October. In October, influenza B virus was also isolated from a 14-year-old in Hawaii.

Influenza A(H3N2) occurred sporadically in Australia and New Zealand, but no major outbreaks were reported. However, from April through September, an increasing number of Asian and Pacific countries including Hong Kong, Singapore, the People's Republic of China, Guam, and Taiwan reported A(H3N2) isolates. Brazil reported a localized outbreak of influenza A(H3N2) in Rio de Janeiro during May and June. In the United States, one patient, a Vermont resident, has had a serologically confirmed case of influenza A(H3N2). The patient was among a group of tourists who developed respiratory illness while on a ship off Alaska in late August (1). Reported by: National Influenza Centers, Microbiology and Immunology Svcs, World Health Organization, Geneva. Contractors of the Acute Respiratory Diseases Program of the National Research Council Board on Science and Technology in Developing Nations, Washington, DC. Naval Medical Research Unit 2, Indonesia. US Air Force School of Aerospace Medicine, San Antonio, Texas. G Ray, MD, Arizona Health Svcs Center, Tucson, Arizona. Participating State Epidemiologists and State Laboratory Directors. Div of Field Svcs, Epidemiology Program Office; WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: International surveillance data confirm the continuing circulation of three antigenically distinct influenza viruses: type A(H3N2), type A(H1N1), and type B. Influenza A(H1N1) and A(H3N2) viruses are antigenically related through internal proteins, rather than through the surface glycoproteins, hemagglutinin (H) and neuraminidase (N). Whereas antibodies that recognize the outer proteins (particularly the hemagglutinin) can neutralize virus infectivity or reduce spread of virus, antibodies to the internal, cross-reactive proteins do not appear to prevent infection. However, immunity to these shared proteins may be important in terminating infection through the actions of cytotoxic T-cells and might contribute to early recovery (4). H3-containing viruses were responsible for the Hong Kong influenza pandemic of 1968, which spread among all age groups, and have evolved antigenic variants responsible for epidemics with associated excess mortality in the United States during seven seasons since then.

H1-containing viruses reappeared in 1977 after a 20-year absence and caused epidemics with low or no mortality during the 1978-79, 1983-84, and 1986-87 influenza seasons. Many persons born before about 1955 are sufficiently immune to H1N1 viruses evolving since 1977 that they are resistant to infection or have mild illnesses. Consequently, in recent years, early recognition of H1N1 virus has always occurred in children or young adults. However, the first recognized A(H3N2) infections in the United States usually involve adults, as they apparently did this year with the tourists in Alaska (1).

Influenza B viruses, which are antigenically distinct from type A viruses, were first recognized in the 1930s. Although variation occurs in the hemagglutinin of type B viruses, the strains represent a continuum, with no distinct subtypes. Despite this, from the mid-1930s until 1970, nine probable epidemics of influenza B (2) were associated with excess mortality. However, from 1970 to 1979, when influenza B epidemics occurred several times, infections appeared to be mainly confined to children or young adults, and no excess mortality occurred. With the appearance of the B/Singapore/79 strain in 1979, the pattern of excess mortality reemerged, and many B virus infections and associated deaths occurred among the elderly (3). Influenza B viruses were also responsible for major outbreaks or epidemics in the United States in 1983-84 (the B/USSR/83 variant) and in 1985-86 (the B/Ann Arbor/86 variant).

Because the degree of spread of current influenza strains is unpredictable and because it is likely from current observations that both type A(H3N2) and type B viruses will circulate this winter, high-risk persons and those providing their care at home or in medical facilities should be encouraged, in advance of any outbreaks in their area, to receive the trivalent vaccine licensed for this year. The available antiviral agent, amantadine, is effective against all known subtypes of influenza A viruses but is ineffective against influenza B viruses. Laboratories providing support for physicians with patients requiring urgent care (e.g., hospitalized patients) should at this time be evaluating their capabilities to perform rapid viral diagnosis so as to differentiate between influenza A and B infections. Information about reagents and procedures for such diagnosis may be obtained from state health department laboratories or from CDC.


  1. CDC. Outbreak of influenza-like illness in a tour group--Alaska. MMWR 1987;36:697-8, 704.

  2. Noble GR. Epidemiological and clinical aspects of influenza. In: Beare AS, ed. Basic and applied influenza research. Boca Raton, Florida: CRC Press, 1982:11-50.

  3. Nolan TF, Goodman RA, Hinman AR, Noble GR, Kendal AP, Thacker SB. Morbidity and mortality associated with influenza B in the United States, 1979-1980. A report from the Center for Disease Control. J Infect Dis 1980;142:360-2.

  4. McMichael AJ, Gotch FM, Noble GR, Beare AS. Cytotoxic T-cell immunity to influenza. N Engl J Med 1983;309:13-7.

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

Page converted: 08/05/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01