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Current Trends Update: Influenza Activity -- United States, 1994-95 Season

In collaboration with the World Health Organization (WHO) international collaborating laboratories and state and local health departments in the United States, CDC conducts surveillance to monitor influenza activity and to determine the antigenic characteristics of circulating strains of influenza viruses. This report describes influenza viruses isolated from sporadic cases of influenza in the United States during July-September 1994 and summarizes influenza surveillance findings from October through mid-November 1994.

From July through September, influenza type A(H3N2) viruses were isolated from sporadic cases in California, Hawaii, Michigan, New York, and South Dakota; influenza type A(H1N1) was reported from Nevada and influenza type B from Texas. All of these isolates were characterized at CDC and are antigenically similar to the A/Shangdong/09/93-like (H3N2), A/Texas/36/91-like (H1N1), and B/Panama/45/90-like influenza virus strains included in the 1994-95 influenza vaccine.

From October 2, when WHO international collaborating laboratories in the United States began seasonal influenza virus surveillance, through November 19, two of 2693 specimens tested for respiratory viruses yielded influenza virus. Influenza type A was identified by antigen detection from nasopharyngeal swab specimens collected November 2 from a patient in New Mexico and November 3 from a patient in New York. Reports from state and territorial epidemiologists and from sentinel physicians have indicated low levels of influenza-like illness nationwide. Reported by: Participating state and territorial epidemiologists and state public health laboratory directors. World Health Organization collaborating laboratories. Sentinel Physicians Influenza Surveillance System of the American Academy of Family Physicians. WHO Collaborating Center for Surveillance, Epidemiology, and Control of Influenza, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Although the time of onset of influenza epidemics can vary substantially by year, the pattern from October through mid-November 1994 was typical for influenza activity in the United States. In some recent influenza seasons (e.g., 1991-92 and 1993- 94) (1,2), influenza activity began earlier than usual; however, regional activity usually does not begin until December, and influenza activity usually peaks during January or February. Accordingly, the Advisory Committee on Immunization Practices recommends that the optimal time for organized vaccination campaigns for persons in high-risk groups is usually from mid-October through mid-November. Vaccine should be offered to high-risk persons up to and even after influenza activity is documented in a community (3); following vaccination, 1-2 weeks are required for the development of protective antibody titers. When influenza vaccine is administered after influenza type A outbreaks have begun in a community, the antiviral drugs amantadine and rimantadine can be administered to protect against influenza until vaccine-induced antibody has developed. These drugs are not effective against influenza type B. Updated recommendations for the use of these drugs will be published in MMWR during December 1994.

Worldwide virologic surveillance is conducted throughout the year to monitor antigenic changes in the circulating influenza virus strains. Through this system, antigenic changes in influenza virus strains have been detected sufficiently early to formulate influenza vaccines that frequently have contained strains similar to those that subsequently have circulated in the United States at epidemic levels. Although influenza activity is difficult to predict, it is expected that during the 1994-95 season in the United States, both type A and type B viruses will circulate.

Information about national influenza surveillance is updated weekly from October through May and is available through the CDC Voice Information System, telephone (404) 332-4555. Information about local influenza activity is available from county and state health departments.


  1. CDC. Influenza -- United States, 1989-90 and 1990-91 seasons. MMWR 1992;41(no. SS-3):35-46.

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

  3. ACIP. Prevention and control of influenza: part I, vaccines -- recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1994;43(no. RR-9).

+------------------------------------------------------------------- ------+ |             | | Erratum: Vol. 43, No. 46 | |             | | SOURCE: MMWR 43(51);961 DATE: Jan 06, 1995 | |             | | In the article "Update: Influenza Activity -- United States, | | 1994-95 Season," an error appeared on page 848. In the first | | sentence of the second paragraph, Minnesota, not Michigan, should | | have been listed among the states that reported sporadic isolates | | of influenza type A(H3N2) during July-September 1994. | |             | +------------------------------------------------------------------- ------+

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