Epidemiologic Notes and Reports Influenza Activity in Civilian and Military Populations and Key Points for Use of Influenza Vaccines

Investigation of influenza-like illness in military personnel has confirmed infections with the A/Taiwan/86(H1N1)-like variant. These outbreaks have provided additional evidence supporting the use of the 1986-1987 supplemental monovalent influenza vaccine in recommended high-risk groups of young adults and also in young adults providing health care or other essential services.

Asia. During April and May 1986, influenza-like activity was reported among military personnel stationed at three U.S. Air Force bases in the Philippines and Japan. Paired sera were collected from eight ill individuals, including five persons who had been vaccinated with trivalent influenza vaccine between October 1985 and January 1986. The geometric mean titer (GMT) determined from hemagglutination inhibition (HI) test results for the acute-phase sera from the vaccinated personnel was 140 for the A/Chile/83(H1N1) antigen and 35 for A/Taiwan/86. Convalescent-phase sera showed a four-fold increase in the GMT (560) for A/Chile/83 and a ten-fold rise in the GMT (370) for A/Taiwan/86. These findings provide circumstantial evidence that illnesses were caused by infections with A/Taiwan/86-like viruses.

Florida. Between October 10 and November 7, 1986, at least 52 active duty personnel at the Key West Naval Base experienced a respiratory illness characterized by feverishness, cough, and sore throat or myalgias. Thirty-four ill persons were members of one 111-person squadron that was interviewed after an outbreak of influenza-like illness, and the others were identified by reviewing the Naval Medical Clinic records. A/Taiwan/86-like virus was isolated from three of four nasopharyngeal cultures collected on November 5 from ill persons. Patients in the squadron ranged from 19 to 39 years of age; 88% of them were 35 years of age. Onset of illnesses occurred from October 19 to November 2. Supplemental monovalent A/Taiwan/86(H1N1) vaccine had not yet been used. The attack rate among squadron members who had been vaccinated with the 1986-1987 trivalent influenza vaccine--which contains A/Chile/83 antigen as its type A(H1N1) component--was 36.5% (23/63); among the unvaccinated, the attack rate was 33.3%(11/33). Other differences between the vaccinated and unvaccinated groups that might affect illness rates were not identified.

Control measures implemented on the naval base included recommending that all active duty service members 35 years of age be vaccinated with the supplemental monovalent influenza A(H1N1) vaccine. All military dependents who were 35 years of age and also in defined high-risk groups and all health care workers 35 years of age were also vaccinated and received a 14-day course of amantadine chemoprophylaxis beginning at the time of vaccination.

Other Reports--United States. Influenza type A(H1N1) virus also has been isolated from patients during outbreaks of influenza-like illness in two other states. In Massachusetts, virus was isolated in mid-November from one student in each of two Boston colleges. Large increases in the numbers of students seen with influenza-like illness were noted at the time the specimens were collected. In New York City, virus was isolated from two young-adult inmates who were ill in mid-November during an ongoing outbreak of influenza-like illness in an adolescent detention center. During the outbreaks in Massachusetts, New York, and Key West, Florida, there was no apparent spread to surrounding communities where influenza-like illness continued to occur at sporadic levels.

Influenza type A(H1N1) virus was also isolated in association with sporadically occurring cases in Oregon, New York, and Texas. In Oregon, virus was isolated in early November from a teenage patient living near Portland. In New York City, from late October to mid-November, type A(H1N1) virus was isolated from five children and two young adults. In Houston, Texas, active surveillance has identified a total of 15 type A(H1N1) virus isolates collected from residents (nearly all children) during late October to mid-November.

Influenza type B virus has been identified from ill persons in California and Texas. In California, virus was isolated from a 77-year-old resident of San Joaquin County who was ill in mid-October. In Texas, a man returning by air from South America in early November had influenza soon after arriving in Houston. His son developed influenza two days later; type B virus was isolated from both father and son. Reported by HM1 RD Huff, USN, Dept of Environmental and Occupational Health, Naval Medical Clinic, Key West, Florida; CDR RL Buck, MC, USN, LCDR DH Trump, MC, USN, Epidemiology Dept, Navy Environmental and Preventive Medicine Unit, No. 2, Norfolk, Virginia; Epidemiology Div, Disease Surveillance Br, Laboratory Br-Virology Section, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas; EE Buff, MS, E Wyner, MT, V Mock, M Wilder, MD, MS, Acting State Epidemiologist, Florida State Dept of Health and Rehabilitative Svcs; B Daidone, K Bromberg, MD, Kings County Hospital, C Braslow, MD, I Spigland, MD, Montefiore Hospital, S Schultz, MD, New York City Dept of Health, D Morse, MD, State Epidemiologist, New York State Dept of Health; V Berardi, L Mofensen, MD, P Etkind, G Grady, MD, State Epidemiologist, Massachusetts Dept of Public Health; Influenza Research Center, Baylor College of Medicine, Houston, C Alexander, MD, State Epidemiologist, Texas Dept of Health; R Schieble, PhD, R Murray, PhD, J Chin, MD, State Epidemiologist, California Dept of Health Svcs; B Matsuda, MR Skeels, PhD, DW Fleming, MD, LR Foster, MD, MPH, State Epidemiologist, Oregon Dept of Human Resources; Div of Field Services, Epidemiology Program Office, WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Influenza A/Taiwan/86(H1N1)-like viruses were first isolated in Asia in early 1986. These viruses circulated in the western pacific region until about mid-year and caused illness primarily in children and young adults living in the region (1,2). Because there is a high degree of antigenic variation between the A/Taiwan/86-like viruses and the A/Chile/83(H1N1) component of the trivalent 1986-1987 influenza vaccine, a supplemental monovalent vaccine containing A/Taiwan/86(H1N1) virus antigen was recommended, particularly for high-risk children and young adults.

The Key West report is the first outbreak of influenza-like illness identified in the United States during the 1986-1987 influenza season, and isolation of influenza A/Taiwan/86-like virus from three of four patients identified this as the etiologic agent. In late September and early October, the U.S. Navy implemented its 1986-1987 trivalent influenza immunization program; the supplemental monovalent influenza immunization program had not yet begun. The finding of similar attack rates among persons receiving the trivalent vaccine and non-vaccinated persons is consistent with previous serologic data (3). It is also consistent with reported data for Air Force personnel that high post-vaccination antibody titers against A/Chile/83 in young adults do not guarantee protection against infection by A/Taiwan/86-like virus.

It is important to note that the influenza vaccination policy of the Armed Forces of the United States differs from the Immunization Practices Advisory Committee (ACIP) recommendations. In addition to following the ACIP recommendations for civilian dependents and health care personnel, the Armed Forces recommend routine vaccination for all military personnel because of the need to prevent influenza outbreaks that could impair a unit's ability to carry out its mission. The decision to give the monovalent A/Taiwan/86 vaccine to all service members 35 years of age stationed at the Key West facility during the outbreak is in keeping with this policy.

The ACIP recommendations for the civilian population are intended to protect individuals who, because of existing medical conditions, are at high risk for severe influenza and serious complications. The presence of influenza type A(H1N1) outbreaks and type B virus infections in the United States emphasizes the need for all high-risk individuals to receive appropriate vaccination, including trivalent vaccine. Although this information has been published previously in the MMWR (2,4,5), it is important to re-emphasize the following key points:

• High-risk persons of all ages should receive the standard trivalent vaccine according to previously published ACIP recommendations.

• The Public Health Service (PHS) urges health care personnel who treat high-risk children or high-risk adults 35 years of age to provide both trivalent and supplemental A(H1N1) influenza vaccines to their patients.

• Vaccination with the trivalent vaccine should not be delayed if the supplemental vaccine is not available at the time the trivalent vaccine would normally be given.

• Supplemental vaccination is of potential benefit to many other groups of young persons to reduce morbidity if A(H1N1) outbreaks occur. The potential for introducing influenza to

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