Recommendation of the Immunization Practices Advisory Committee (ACIP) Influenza Vaccines 1982-1983
This revision of the influenza vaccine recommendations updates information on influenza activity in the United States for the 1981-1982 influenza season (superseding MMWR 1981;30:279-88) and provides information on the vaccine to be available for the 1982-1983 influenza season. INTRODUCTION
Influenza virus infections occur every year in the United States but vary greatly in incidence and geographic distribution. Infections may be asymptomatic, or they may produce a spectrum of manifestations ranging from mild upper-respiratory infection to pneumonia and death. Influenza A and B viruses are responsible for only a small proportion of all respiratory disease, but they are unique in their ability to cause periodic widespread outbreaks of febrile respiratory illness among adults and children.
Influenza epidemics are frequently associated with deaths in excess of the number normally expected. More than 200,000 excess deaths are estimated to have occurred in association with influenza epidemics in the United States during 1968-1981. Excess deaths in this period were attributable mainly to influenza A viruses, although influenza B epidemics were occasionally associated with excess deaths, as in 1979-1980. Epidemics of influenza B, and to a lesser extent of influenza A, infection have been associated with an increased incidence of Reye syndrome among children and adolescents in the United States.
Efforts to reduce the impact of influenza in the United States have been aimed at protecting persons at greatest risk of serious illness or death. Observations during influenza epidemics indicate that most influenza-related deaths occurred among chronically ill children and adults and older persons, especially those 65 years old. Annual vaccination is therefore recommended for these medically high-risk persons.
Influenza A viruses are classified into subtypes on the basis of 2 antigens: hemagglutinin (H) and neuraminidase (N). Three subtypes of hemagglutinin (H1,H2, H3) and 2 subtypes of neuraminidase (N1, N2) are recognized among influenza A viruses that have caused widespread human disease. Immunity to these antigens, especially hemagglutinin, reduces the likelihood of infection and the severity of disease if a person does become infected. However, there may be sufficient antigenic variation (antigenic drift) within the same subtype over time so that infection or vaccination with 1 strain may not induce immunity to distantly related strains. Although influenza B viruses have shown much more antigenic stability than influenza A viruses, antigenic variation does occur. As a consequence, the characteristics of antigenic properties of current strains provide the basis for selecting virus strain(s) to be included in the vaccine.
During the 1981-1982 winter, influenza activity was generally low in the United States, with no apparent peaks of excess mortality. Less than half the usual number of virus isolates were reported to CDC. In many states, influenza B viruses were shown to be the cause of localized outbreaks among school-age children. Several nursing-home outbreaks, some with associated mortality, were also confirmed to be caused by influenza B viruses. The strains of virus isolated were closely related antigenically to B/Singapore/222/79. Sporadic illnesses and a few focal outbreaks caused by influenza A(H1N1) viruses also occurred among children and young adults, but these viruses were less prevalent than influenza B. Influenza A(H1N1) isolates were, as in 1980-1981, similar to A/England/333/80, which can be shown by laboratory tests to be slightly different from A/Brazil/11/78, the current vaccine strain. Measurement of antibody responses of persons receiving vaccines containing A/Brazil/11/78 antigen, however, indicates that these vaccines should protect against A/England/333/80-like H1N1 strains. Most information about strains of influenza A(H3N2) likely to be prevalent in 1982-1983 is derived from reports and analyses of viruses isolated in 1981 in Asia. There was little circulation of H3N2 strains in the Americas or Europe during the 1981-1982 influenza season. In 1981, most influenza A(H3N2) virus isolates from Asia and the Southern Hemisphere were similar to strains circulating previously. Some additional variants were identified, but they did not become predominant at any time during the year or appear to cause any epidemics. INFLUENZA VACCINES FOR 1982-1983
The specific antigens and their potency in the vaccine will be the same as in 1981-1982: 15 ug each of hemagglutinin of A/Brazil/78(H1N1), A/Bangkok/79(H3N2), and B/Singapore/79 viruses per 0.5-ml dose.
Adults and children greater than or equal to 13 years old will require only 1 dose. Children 13 years old are less likely than older children or adults to have been previously infected with strains related to each of the vaccine components. Therefore, because of their potentially lower level of immunologic priming, children in the 13-year age group should receive 2 doses of vaccine. However, children who have already had at least 1 of the influenza vaccines recommended for use from 1978 to 1982 will require only 1 dose of the 1982-1983 vaccine. The 1982-1983 vaccines will be available as whole-virion (whole-virus) and sub-virion (split-virus) preparations. Past data indicate that split-virus vaccines have been associated with somewhat fewer side effects than whole-virus vaccines among children. Thus, only split-virus vaccines are recommended for persons 13 years old. VACCINE USAGE General Recommendations Annual vaccination is strongly recommended:
risk of adverse consequences from infections of the lower respiratory tract because of a pre-existing medical condition.
Conditions predisposing to such increased risk include:
For all older persons, particularly those 65 years old, because the risk of death during influenza outbreaks generally increases with age.
In balancing the benefits, risks, and costs for the community, some localities have elected to vaccinate persons who provide essential community services and medical-care personnel who also are at increased risk of exposure. Uniform recommendations cannot be made in this regard. However, vaccination programs for groups who provide community services should not take precedence over vaccination of persons specified to be at high risk.
Table 1 summarizes vaccine and dosage recommendations by age group for 1982-1983. Use in Pregnancy
Physicians should evaluate a pregnant woman's need for influenza vaccination on the same basis used for other persons; that is, vaccination should be advised for a pregnant woman who has any underlying high-risk condition. Only in the pandemics of 1918-1919 and 1957-1958 was there persuasive evidence that influenza infection increased maternal mortality.
There is no evidence to suggest that influenza vaccine carries any maternal or fetal risk, and, because it is inactivated, the vaccine does not share any of the theoretical risks of live-virus-vaccine infection of the fetus. Nonetheless, when vaccine is to be given in pregnancy, waiting until the second or third trimester is a reasonable precaution to minimize any concern over teratogenicity. Side Effects and Adverse Reactions
Vaccines used in recent years have generally been associated with only a few reactions; less than one-third of vaccinees have been reported to have local redness and induration for 1 or 2 days at the site of injection.
Systemic reactions have been of 3 types:
toxicity, although infrequent, most often affect children and others who have had no experience with the influenza virus antigens contained in the vaccine. These reactions, which begin 6-12 hours after vaccination and persist 1-2 days, are usually attributed to the influenza virus itself (even though it is inactivated) and constitute most of the side effects of influenza vaccination.
2. Immediate, presumably allergic, responses such as flare and wheal or various respiratory expressions of hypersensitivity occur extremely rarely after influenza vaccination. They probably result from sensitivity to some vaccine component--most likely residual egg protein. Although current influenza vaccines contain only a small quantity of egg protein, on rare occasions they can induce hypersensitivity reactions. Individuals with anaphylactic hypersensitivity to eggs should not be given influenza vaccine. This would include persons who, on eating eggs, develop swelling of the lips or tongue or experience acute respiratory distress or collapse.
3. In 1976, a temporal association (i.e., within 10 weeks of vaccination) was noted between Guillain-Barre syndrome (GBS) and administration of A/New Jersey/76 (swine) influenza vaccine. Vaccinated adults had an excess frequency of GBS at the rate of approximately 10 cases/1 million persons vaccinated. This incidence of GBS was 5-6 times higher than the comparable average reported incidence for unvaccinated persons. An active surveillance system for GBS was initiated in 1978 and was maintained for 3 years. No significant excess risk of GBS was found for recipients of influenza vaccine. Available evidence indicates that any risk of GBS from influenza vaccine appears to be far lower than the risks associated with influenza among persons for whom the vaccine is indicated. SUPPLEMENTARY MEASURES
Annual vaccination continues to be the most important way to prevent influenza and should be routine for all persons at high risk of serious and/or fatal disease. Supplementary measures intended to reduce the likelihood of exposure in community outbreaks, such as limiting the number of gatherings of large groups, may delay spread but are not uniformly effective.
Amantadine hydrochloride, an antiviral drug, can play a supplementary role in helping prevent influenza A for certain persons and circumscribed groups. It is not a substitute for vaccine and not generally applicable to public health practice, but it may be useful for persons who need protection but have not been vaccinated.
Amantadine protects only against influenza A, not influenza B, infection and must be taken each day for the duration of the epidemic (6-8 weeks, generally) or until active immunity can be expected to develop (about 10-14 days after vaccination). Precautions must be taken for patients with certain chronic conditions, and there are sometimes mild but occasionally troublesome side effects--especially among older patients. Amantadine, a prescription drug, must be ordered and monitored by a physician. Dosage, precautions, and other information on use are specified in the drug's labeling.
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