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Update: Influenza Activity -- Worldwide, 1995

From October 1994 through August 1995, influenza activity occurred at low to moderate levels in most parts of the world. Influenza activity usually was associated with the cocirculation of influenza types A and B viruses. Overall, influenza A(H3N2) was the predominant influenza A subtype, but isolation of influenza A(H1N1) viruses increased during this period and was the most frequently isolated influenza virus in Australia from March through August. This report summarizes influenza activity worldwide from March through August 1995.

Africa. In Madagascar, circulation of influenza A(H3N2) began during January and continued through April; during April, influenza A(H1N1) was isolated in Madagascar. In South Africa, influenza A(H1N1) and influenza A(H3N2) viruses were isolated from samples collected for respiratory virus isolation during May-July. Influenza B viruses also were detected in South Africa during July. Influenza A(H3N2) was isolated in Zambia during June.

Asia. Influenza A(H1N1), A(H3N2), and influenza B viruses were isolated during every month from March through June in Asia. Influenza A(H1N1) viruses were isolated in Guam during May, in Hong Kong during March and April, and in Thailand during April, May, and July. Influenza A(H1N1) and influenza B viruses were isolated during outbreak-level activity in Taiwan during April-June. Other countries reporting influenza B activity associated with sporadic cases or outbreaks included China, Hong Kong, Japan, Korea, Singapore, and Thailand. Influenza A(H3N2) viruses were isolated in China in association with sporadic and outbreak activity during April and from sporadic cases during June. Influenza A(H3N2) viruses also were isolated in Korea and Thailand during March, in Guam during March and May, in Hong Kong during March and July, and in Japan during April. Singapore reported influenza A activity every month from March through June; influenza A (H3N2) isolates were subtyped during March, May, and June. Additional influenza A viruses, subtype unknown, were identified by antigen-detection methods in Malaysia during March.

Europe. Activity in Europe began with an outbreak of influenza B virus in Portugal during October 1994 and continued from March through June. Influenza A(H3N2), A(H1N1), and influenza B viruses were isolated during this period. Outbreak activity was last reported from Romania and Bulgaria during May. Circulation of influenza A(H1N1) viruses increased from March through May and was associated with an outbreak in members of a military unit in Bulgaria. Detection of both influenza A and influenza B viruses continued in France during June.

North America. Influenza A(H3N2) viruses predominated during the 1994-95 season, but influenza B and A(H1N1) viruses also were isolated. Following peak activity during February through early March in the United States, influenza A(H3N2), A(H1N1), and influenza B viruses continued to be isolated every month during March-June. Influenza A(H1N1) was isolated from one patient in Arizona during July. The number of influenza A(H1N1) isolates increased during February-May; most were collected during May. Late-season influenza activity also occurred in Canada. The most recent detection of influenza B virus was reported during the week ending June 3, and reports of influenza A virus isolation or detection continued during July and August. As in the United States, influenza A(H1N1) viruses were reported in Canada during the latter part of the influenza season.

Central and South America. Influenza A and influenza B viruses were detected during the 1994-95 influenza season in South America with influenza A predominating. Brazil reported detection of influenza A from February through April. In Chile, outbreaks of influenza were detected during May-July; influenza A predominated, but influenza B also was detected. In Argentina, the first case of influenza A was diagnosed in late May and outbreaks were reported during June and July; influenza A predominated, but influenza B also was detected. Reports of influenza-like illness increased in Uruguay during May-July, and influenza A virus was identified by antigen-detection methods. Influenza A virus was detected in one patient in Panama during June, followed by a single detection of influenza B virus during July. All influenza A viruses from Argentina, Brazil, and Chile subtyped or further identified by serologic testing were influenza A(H3N2). No influenza A(H1N1) isolates were reported from Central or South America.

Oceania. The influenza season began early in Australia with outbreaks in the Northern Territory at the end of March. Both influenza A(H1N1) and influenza B viruses were isolated during the outbreak, with influenza A(H1N1) viruses predominating. Influenza-like illness, as reported by general practitioners, increased through the beginning of July and remained stable during mid-July through the beginning of August. As the season progressed, the number of influenza B isolates increased; however, influenza A(H1N1) viruses remained more prevalent. Influenza A(H3N2) viruses were rarely isolated. In contrast, influenza B predominated in New Zealand through July, but the proportion of influenza A(H3N2) viruses isolated increased during July. Both influenza A(H3N2) and influenza B viruses were associated with outbreaks at the end of July.

Characterization of influenza virus isolates. From October 1, 1994, through August 15, 1995, a total of 760 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, 535 (70%) were from North America, 76 (10%) from Europe, 130 (17%) from Asia, and 19 (3%) from South America and Oceania. Of the viruses subtyped, 396 (52%) were influenza A(H3N2), 91 (12%) A(H1N1), and 273 (36%) influenza B. Of the 396 influenza A(H3N2) isolates characterized, 227 (57%) were antigenically related to A/Shangdong/09/93, the 1994-95 vaccine strain, and 164 (41%) were more closely related to A/Johannesburg/33/94, the A(H3N2) component of the 1995-96 influenza vaccine. Of the 273 influenza B viruses, 66 (24%) were similar to B/Panama/45/90, the 1994-95 vaccine component, and 202 (74%) were similar to B/Beijing/184/93, the 1995-96 vaccine component. Of the 91 influenza A(H1N1) viruses, 12 (13%) were A/Texas/36/91-like, and 79 (87%) were more closely related to the antigenically similar A/Taiwan/01/86-like viruses (1,2). The influenza A(H1N1) component of the 1995-96 vaccine is A/Texas/36/91.

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: Based on recent patterns of worldwide influenza activity, the 1995-96 influenza season in the United States may be characterized by cocirculation of influenza type A(H3N2), type A(H1N1) and type B. However, because specific patterns of influenza activity cannot be predicted with certainty, the extent of virus circulation and the relative prevalence of the different influenza virus strains is unknown. Therefore, influenza vaccination should be offered each fall to persons at high risk for influenza-related complications and their close contacts and to health-care providers.

The influenza vaccine is 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. Most of the influenza viruses isolated since March 1995 are antigenically similar to the 1995-96 influenza vaccine strains (CDC, unpublished data, 1995).

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 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 who therefore may be at risk for developing Reye syndrome after influenza. Vaccination also is recommended for health-care workers and other persons who are in close contact with persons in high-risk groups, including household members. Women who will be in the third trimester of pregnancy during the influenza season may be at increased risk for medical complications following influenza infection and should consult with their health-care providers about receiving the vaccine. Influenza vaccine also can be administered to anyone who wants to reduce the likelihood of acquiring influenza.

Beginning in September, persons at high risk who are seen by health-care providers for routine care or as a result of hospitalization should be offered influenza vaccine. The optimal time for organized vaccination campaigns is mid-October through mid-November. Health-care providers should continue to offer vaccine to high-risk persons up to and even after influenza activity is documented in a community.

Information about influenza surveillance is available through the CDC Voice Information System (influenza update) by telephone ({404} 332-4555) or fax ({404} 332-4565) (document number 361100) 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 MMWR, and information on local influenza activity is available through county and state health departments.

References

  1. CDC. Update: influenza activity -- United States and worldwide, 1993-94 season, and composition of the 1994-95 vaccine. MMWR 1994;44:179-83.

  2. CDC. Update: influenza activity -- United States and worldwide, 1994-95 season, and composition of the 1995-96 vaccine. MMWR 1995;44:292-5.


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