Epidemiologic Notes and Reports Update on Influenza Activity in the United States, Availability of Influenza Vaccines, and Recommendations for the Use of Vaccines and Amantadine

Update: Influenza Activity -- United States

Reports of outbreaks of influenza-like illness increased throughout the continental United States in December. For the week ending January 3, eight states and Puerto Rico reported widespread outbreaks of influenza-like illness, and 17 states and the District of Columbia reported regional outbreaks of influenza-like illness. Most of the reported outbreaks occurred in schools and colleges. No confirmed outbreaks of influenza have been reported in nursing homes or other institutions caring primarily for elderly persons. Consistent with the apparently low impact of the current A(H1N1) strain on the elderly, there has not been a significant increase in mortality from influenza and pneumonia thus far this season. Thirty-four states and the District of Columbia have now reported isolates of A(H1N1) influenza virus (Figure 1). So far this season, influenza type A(H3N2) and type B have been isolated only in association with sporadically occurring cases. Type A(H3N2) influenza has been isolated only in Arizona. Type B influenza has been isolated in two states, California and Texas. Availability of Influenza Vaccines and Recommendations and Precautions for the Use of Amantadine

Two of the three United States manufacturers of influenza vaccine, Parke-Davis and Wyeth Laboratories, have reported that they have sold all influenza vaccine, both trivalent and monovalent, produced for the 1986-87 season. The third manufacturer, Connaught Laboratories, reported having limited supplies of both the standard trivalent and the supplemental monovalent (A/Taiwan/86) vaccines as of January 5.

The number of unused distributed doses of influenza vaccine is not known. However, spot shortages exist in at least some parts of the country because some state health departments, institutions, and private physicians have reported being unable to replenish dwindling or exhausted supplies. Reported by State and Territorial Epidemiologists; State Laboratory Directors; Div of Immunization, Center for Prevention Svcs, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Although influenza vaccine should be administered before the influenza season, unaffected persons can receive the vaccine after influenza activity begins. Health care personnel should use available vaccine in accordance with the priorities established by the Immunization Practices Advisory Committee (1,2). Groups at greatest medical risk of influenza-related complications should receive vaccine before other groups. In particular, remaining supplies of A/Taiwan/86 vaccine should only be used for high-risk persons 35 years of age. High-risk persons of all ages should receive the standard trivalent vaccine.

If patients are vaccinated after local outbreaks of influenza type A have begun, chemoprophylaxis with amantadine may be indicated for the 2 weeks following vaccination, since it takes about 2 weeks to develop an antibody response. Amantadine prophylaxis should also be considered for high-risk patients if vaccine is unavailable. However, for continuous protection against circulating strains of type A influenza, unvaccinated persons must take amantadine throughout the period of local influenza type A virus circulation, which can be 6 to 12 weeks.

Amantadine may also be used for treating influenza type A. When given within the first 48 hours of illness, amantadine has been shown to reduce the severity and shorten the duration of illness in healthy adults. Although the efficacy of amantadine therapy in preventing complications due to influenza is unknown, it should be considered for high-risk patients who develop influenza-like illness during known influenza type A activity.

In determining whether to use amantadine for prophylaxis or treatment of individual patients, the following information should be considered:

1. In controlled studies, 5% to 10% of healthy young adults taking amantadine have reported side effects involving the central nervous system such as insomnia, nervousness, lightheadedness, and impaired concentration. Such side effects are usually mild and cease soon after amantadine is discontinued.

2. Amantadine is not metabolized and is excreted unchanged by the kidneys. When amantadine is administered to patients with impaired renal function, the dose should be reduced. Because of the diminished renal function associated with normal aging, it is recommended that the dosage in persons greater than or equal to 65 years of age not exceed 100 mg/day. Tables for estimating dosage based on creatinine clearance for persons with known renal disease have been published (1,3). Since these tables may only provide a rough estimate of the optimal dose for a given patient, it is especially important that patients with renal disease as well as persons greater than or equal to 65 years of age, their relatives, and/or caretakers be informed about potential side effects so that the dosage may be adjusted if necessary.

3. Any patient with an active seizure disorder should not be given more than 100 mg of amantadine daily.

4. The use of amantadine in children 1 year of age has not been adequately evaluated. The approved dosage for children 1-9 years of age is 4.4 to 8.8 mg/kg/day, not to exceed 150 mg/day. To reduce the risk of toxicity, physicians should consider prescribing the lower range of the approved dosage for children.

References

1. ACIP. Prevention and control of influenza. MMWR 1986;35:317-26,331.

2. ACIP. Monovalent influenza A(H1N1) vaccine, 1986-87. MMWR 1986;35:517-21.

3. Horadam VW, Sharp JG, Smilack JD, McAnalley BH, Garriott JC, Stephens MK, et al. Pharmacokinetics of amantadine hydrochloride in subjects with normal and impaired renal function. Ann Intern Med 1981;94:454-8.

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