Current Trends Update: Influenza Activity -- Worldwide, 1994

From October 1993 through August 1994, influenza activity occurred at moderate to moderately severe levels worldwide. Influenza A(H3N2) viruses predominated during the 1993-94 season, but influenza B viruses also were isolated from persons with sporadic illness and from outbreak-associated cases. Cocirculation of influenza A(H3N2) and influenza B viruses is continuing throughout the world; however, the isolation of influenza A(H1N1) viruses has been extremely rare (1). This report summarizes influenza activity worldwide from March through August 1994.

Africa. In Africa, influenza activity occurred from May through July. Zambia and South Africa reported influenza B as the predominant virus isolated. South Africa identified sporadic cases of influenza A(H3N2).

Asia. Cocirculation of influenza A(H3N2) and influenza B viruses has been reported in Asia. During March and April, both influenza A and B were reported during outbreaks in Taiwan. Thailand reported influenza B in March and April and influenza A and B from May through July, with influenza B predominating. Hong Kong reported only influenza B through June; during July, moderate levels of influenza A(H3N2) activity occurred. Since March, only influenza B viruses have been isolated in China in association with outbreaks or sporadic cases of influenza-like illness (ILI).

Europe. In March, all reporting countries except Russia reported influenza activity either at or approaching normal levels. In Russia, influenza activity continued through March with the isolation of both influenza A and B viruses. Isolation of influenza A(H3N2) viruses from sporadic cases was reported in the United Kingdom in June. Since June, the Netherlands and the United Kingdom each have reported one influenza B isolate.

North America. In the United States, type A(H3N2) viruses from outbreaks continued to be reported in March along with isolates from sporadic cases that continued into April. Sporadic cases of influenza B occurred in March, April, and May. Influenza A viruses were isolated from six sporadic cases in July and August. Of these, three have been indentified as influenza A(H3N2). Canada reported the detection of both influenza A and B through the beginning of May.

Central and South America. Based on serologic studies, an increase in acute respiratory illness (ARI) in Panama in June was attributed to influenza A(H3N2). Sporadic isolation of influenza A and B viruses was reported in Argentina, Brazil, and Chile from April through June. In April, an outbreak of ARI associated with influenza A(H3N2) viruses was reported in Porto Velho, Brazil. Influenza A(H3N2) predominated in Santiago, Chile, in mid-July when ILI morbidity peaked.

Oceania. In Australia, influenza activity increased markedly by the end of June, and outbreaks occurred throughout the country in July. Epidemic-level activity was reported in mid-August in Newcastle. Although most isolates were influenza A(H3N2) viruses, influenza B viruses were isolated from sporadic cases. Outbreaks of influenza occurred in New Zealand from May through July; influenza A(H3N2) viruses were isolated more frequently than influenza B viruses.

Characterization of influenza virus isolates. From October 1, 1993, through August 31, 1994, 648 influenza isolates collected worldwide were antigenically characterized by the World Health Organization Collaborating Center for Surveillance, Epidemiology, and Control of Influenza at CDC. Of these, 369 (57%) were from North America, 155 (24%) from Asia, and 124 (19%) from Europe. Of 648 viruses analyzed, 519 (80%) were subtyped as influenza A(H3N2) viruses, and 129 (20%) were influenza B viruses. More than 99% of influenza A(H3N2) viruses analyzed were antigenically related to A/Beijing/32/92 (the vaccine strain for 1993-94); however, 125 (24%) of these viruses were more closely related to A/Shangdong/09/93, a variant of A/Beijing/32/92 that was selected for the vaccine strain for 1994-95 (1). Of the 129 influenza B viruses analyzed, 102 (79%) were closely related to the 1993-94 and 1994-95 influenza B vaccine strain, B/Panama/45/90. Although influenza A(H1N1) viruses have been isolated rarely, those characterized are similar antigenically to A/Texas/36/91, the 1994- 95 vaccine strain. Reported by: World Health Organization National Influenza Centers, Communicable Disease Div, World Health Organization, Geneva. World Health Organization Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, Influenza Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The antigenic components of influenza vaccine are updated annually to include viruses that are antigenically similar to the strains of the three distinct groups of influenza viruses that have been in worldwide circulation. The vaccine for the 1994- 95 season contains A/Shangdong/09/93-like (H3N2), B/Panama/45/90-like, and A/Texas/36/91-like (H1N1) antigens . Most of the influenza viruses isolated since March 1994 are antigenically similar to the 1994-95 influenza vaccine strains. Based on recent patterns of worldwide influenza activity, both influenza type A(H3N2) and type B are expected to circulate in the United States during the 1994-95 influenza season.

Vaccination against influenza is recommended by the Advisory Committee on Immunization Practices for 1) persons aged greater than or equal to 65 years; 2) persons who reside in nursing homes or other chronic-care facilities; 3) persons with chronic cardiovascular or pulmonary disorders, including children with asthma; 4) persons who required medical follow-up or hospitalization during the previous year because of diabetes and other chronic metabolic diseases, renal dysfunction, hemoglobinopathies, or immunosuppression; and 5) children and adolescents who are receiving long-term aspirin therapy and therefore may be at risk for developing Reye syndrome after influenza. In addition, vaccination is recommended for health-care workers and other persons who are in close contact with persons in high-risk groups, including household members.

The optimal time for organized vaccination campaigns is from mid-October through mid-November. However, persons at high risk who visit health-care providers for routine care or who are hospitalized should be offered influenza vaccine before the recommended time. In addition, health-care providers should continue to offer vaccine to high-risk persons even after influenza activity is documented in a community.

Information regarding influenza surveillance is available through the CDC Voice Information System (influenza update), telephone (404) 332-4555, or through the CDC Information Service on the Public Health Network electronic bulletin board. From October through May, the information is updated weekly. Periodic updates about influenza are published in the MMWR, and information on local influenza activity is available through county and state health departments.

Reference

1. CDC. Update: influenza activity -- United States and worldwide, 1993-94 season, and composition of the 1994-95 influenza vaccine. MMWR 1994;43:179-83.

   
   

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