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Antigenic Variation Continued occasion resulted in diminished vaccine efficacy, such as the failure of A/Port Chalmers/1/73 to protect against AVictoria/3/75 (2). However, reduced vaccine efficacy has not always occurred in such situations. In 1972, vaccine containing AlAichi/2/68 reduced cases of influenza by 60% in an outbreak caused by the antigenic drift variant A/England/42/72 (3), and, in 1977, AVictoria/3/75 vaccine protected adults from A/Texas/1/77 infection with 80% efficacy (4). The mechanism of such cross (heterovariant) protection is not precisely known. Although antigenic variants differ in some epitopes on the hemagglutinin, they also share other common hemagglutinin epitopes. Because type A(H3N2) viruses have circulated since 1968, most of the population has been primed by previously circulating strains and is, therefore, more responsive to heterovariant immunization. In addition, the antigenic changes described occurred in the hemagglutinin surface glycoprotein. Significant protection from illness may also be induced by the neuraminidase surface glycoprotein (5,6), which has shown less evidence of antigenic drift. Still other factors, such as the capacity of a strain to spread in the population, can emerge independently from changes in the antigenic properties of the hemagglutinin. Therefore, vaccine efficacy cannot be determined until placebo-controlled double-blind trials have been completed.

Nevertheless, laboratory studies, as well as preliminary observations during outbreaks of influenza A(H3N2) among high-risk residents of nursing homes, suggest that the A/Leningrad/360/86 component of the current vaccine may not provide optimal protection against presently circulating strains. These findings emphasize the need for health-care providers to be aware of the recommendations for use of the antiviral drug amantadine for controlling outbreaks and for prophylaxis or treatment of unprotected patients (7). Because amantadine, which is a prescription drug, must be given before exposure to prevent infection or within the first 1 or 2 days after onset of illness for treatment, contingency plans for its rapid use are needed. These plans include obtaining a physician's order to give the drug to high-risk patients at the first signs of influenza illness, knowing the precautions concerning dosage of the drug (particularly for persons with known renal insufficiency or with presumed reduced renal function, such as those over 64 years of age), and arranging for an adequate supply of the drug.

A fact sheet on amantadine, directed particularly at use in institutions caring for high-risk persons, is available through the Office of Public Inquiries, Centers for Disease Control, 1600 Clifton Road, NE, Atlanta, Georgia 30333. References 1. Centers for Disease Control. Update: influenza activity – United States. MMWR 1988;

37:49-50. 2. Barker WH, Mullooly JP. Effectiveness of inactivated influenza vaccine among non

institutionalized elderly persons. In: Kendal AP, Patriarca PA, eds. Options for the control of influenza: proceedings of a Viratek-UCLA symposium held in Keystone, Colorado,

April 20-25, 1985. New York: Alan R Liss, Inc, 1985:169-82. 3. Stiver HG, Graves P, Eickhoff TC, Meiklejohn G. Efficacy of "Hong Kong" vaccine in

preventing "England" variant influenza A in 1972. New Engl J Med 1973;289:1267-71. 4. Meiklejohn G, Eickhoff TC, Graves P, I J (sic). Antigenic drift and efficacy of influenza virus

vaccines, 1976-1977. J Infect Dis 1978;138:618-24. 5. Monto AS, Kendal AP. Effect of neuraminidase antibody on Hong Kong influenza. Lancet

1973;1:623-5.

Antigenic Variation Continued 6. Couch RB, Kasel JA, Gerin JL, Schulman JL, Kilbourne ED. Induction of partial immunity to

influenza by a neuraminidase-specific vaccine. J Infect Dis 1974;129:411-20. 7. Immunization Practices Advisory Committee. Prevention and control of influenza. MMWR

1987;36:373-80,385-7.

Current Trends

Changes in Premature Mortality

United States, 1979-1986

Premature mortality in the United States, as measured in total years of potential life lost (YPLL) before age 65 (1), has been analyzed for data collected annually since 1979.* The overall trend from 1979 to 1986 was toward lower YPLL and YPLL rates, even though the number and rate of YPLL increased from 1984 to 1986 (Table V, page 45).

The total number of YPLL decreased by 6.0%, and the rate of YPLL per 1,000 persons fell by 13.3% during the period 1979-1986 (Table 1). The greatest absolute rate decline from 1979 to 1986 was in YPLL due to unintentional injuries (Figure 1). The ranking of the leading causes of YPLL changed only slightly from 1979 to 1986, with the exception of the addition of the acquired immunodeficiency syndrome (AIDS) (Table 1). Fewer than five AIDS deaths were recorded in 1979; however, by 1986, AIDS had become the eighth leading cause of YPLL and accounted for 2.0% of total YPLL. *The period for which U.S. mortality data coded according to the International Classification of Diseases, Ninth Revision, (ICD-9) are available.

TABLE 1. Ranking of leading causes of years of potential life lost (YPLL) before age 65 and percentage of change in rates United States, 1979 and 1986

Ranking

YPLL Rate Change Cause of Mortality

1979
1986

1979–1986 (%) All Causes

(-13.3)

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Premature Mortality Continued

From 1979 to 1986, the rate of YPLL decreased for ten of the leading causes of death and increased for three. Unintentional injuries accounted for the largest portion of the decrease (30.0%) among the causes of death with rate decreases. Most of the decline in injuries occurred between 1980 and 1982 and is attributable to a decrease in motor vehicle-related deaths in the 15- to 24-year age group. Prematurity (respiratory distress syndrome and disorders relating to short gestation and unspecified low birthweight) had the largest relative decline in rate of YPLL per 1,000 persons. In large part, this decline was due to a greater than one-third reduction in the rate of infant deaths due to respiratory distress syndrome. Prematurity (-17.4%) and diseases of the heart (-14.0%) followed injuries in contributing to the overall decline in YPLL rates from 1979 to 1986. Reported by: Epidemiologic Studies Br, Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, CDC. Reference 1. Centers for Disease Control. Premature mortality in the United States: public health issues in

the use of years of potential life lost. MMWR 1986;35(suppl 2S).

FIGURE 1. Rates of years of potenital life lost (YPLL) for causes with rate changes >0.5, by year United States, 1979-1986

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Indicators of influenza activity are increasing throughout the United States. For the week ending January 23, 1988, 2 states* reported widespread outbreaks of influenzalike activity, and 10 states reported regional influenza-like activity. This is the second week with reports of widespread influenza-like activity. For the report week ending January 16, 1988, physicians reported that 6% of their outpatients were diagnosed as having influenza-like illness. While this level is the highest reported so far this year, it is below the usually observed peak of 10%-12%.

Influenza A(H3N2), the predominant type this season, has now been identified in 25 states (Figure 1). Eight states have reported isolates of influenza A, subtype pending. ** Outbreaks of influenza A(H3N2) have now been documented in nursing homes in Minnesota, New York, and Wisconsin. In addition, an outbreak of influenzalike illness began during late December and continued into January in a facility for the mentally handicapped in South Dakota; both residents and staff were affected. South Dakota also reported an abrupt increase in school absenteeism due to influenza-like illness among students and staff. Sporadically occurring cases of Influenza B

*Hawaii and South Dakota. *Idaho, Kentucky, Mississippi, Missouri, Montana, Nebraska, Texas, Utah, Washington, and Wisconsin. "Reported by approximately 160 physician members of the American Academy of Family Physicians. A patient with a temperature >37.8 °C (100 °F) and at least cough or sore throat was considered to have influenza-like illness. "Arizona, California, Colorado, Florida, Idaho, lowa, Kansas, Michigan, Minnesota, Missouri, Montana, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Tennessee, Texas, Utah, Washington, Wisconsin, and Wyoming. **Hawaii, Indiana, Kentucky, Louisiana, Nebraska, Mississippi, North Carolina, and Virginia.

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FIGURE 1. States reporting isolates of influenza, by type 19, 1987-January 25, 1988

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Update: Influenza Activity Continued occurring cases of influenza B have been reported from 6 states; however, influenza B has not been associated with any outbreaks.

In the 121 cities reporting regularly to CDC, 5.9% of deaths were associated with pneumonia and influenza (P&I) for the week ending January 16, 1988. This percentage does not exceeded the epidemic threshold's for the influenza season to date (Figure 2). Reported by: Participating State and Territorial Epidemiologists and State Laboratory Directors. Sentinel Physicians of the American Academy of Family Physicians. WHO Collaborating Laboratories. WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC. Reference 1. Lui K-J, Kendal AP. Impact of influenza epidemics on mortality in the United States from

October 1972 to May 1985. Am J Public Health 1987;77:712-6. **Arizona, Hawaii, Montana, New York, Ohio, and Tennessee. $$ The epidemic threshold for the 1987/88 influenza season was estimated at 1.645 standard deviations above the values projected on the basis of a periodic regression model applied to observed P&l deaths for the previous 5-year period, but excluding the observations during influenza outbreaks (1).

FIGURE 2. Pneumonia and influenza deaths as a percentage of total deaths* United States, July 1984 January 16, 1988

A/Mississippi/1/85(H3N2)

A/Taiwan/1/86(H1N1)
B/Ann Arbor/1/86 &
A/Mississippi/1/85(H3N2)

PERCENT

OBSERVED NUMBER
EPIDEMIC THRESHOLD

EXPECTED NUMBER 3 Week No. 28 36 44 52 4 12 20 28 36 44 524 12 20 28 36 44 534 12 20 28 36 44 524 12 20 26

Month JAS OND JFM A M J J A S O N D EM A M J J A SOND FM A M J J A SONDJEMANJ
Year 1984

1985
1986

1987

1988 *Reported to CDC from 121 cities in the United States. Pneumonia and influenza deaths include all deaths for which penumonia is listed as a primary or underlying cause or for which influenza is listed on the death certificate.

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