Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP)

Nicole M. Smith, PhD; Joseph S. Bresee, MD; David K. Shay, MD; Timothy M. Uyeki, MD; Nancy J. Cox, PhD; Raymond A. Strikas, MD


Morbidity and Mortality Weekly Report. 2006;55(27):1-41. 

In This Article

Additional Information Regarding Vaccination of Specific Populations

Because children aged 6-23 months are at substantially increased risk for influenza-related hospitalizations and because children aged 24-59 months are at increased risk for influenza-related clinic and emergency department visits,[152] ACIP recommends vaccination of children aged 6-59 months. The current LAIV and inactivated influenza vaccines are not approved by FDA for use among children aged <6 months, the pediatric group at greatest risk for influenza-related complications.[58,153,154] Vaccination of their household contacts and out-of-home caregivers also is recommended because it might decrease the probability of influenza virus infection among these children.

Studies indicate that rates of hospitalization are higher among young children than older children when influenza viruses are in circulation.[57,59,60,61,62,155,156,157] The increased rates of hospitalization are comparable with rates for other groups considered at high risk for influenza-related complications. However, the interpretation of these findings has been confounded by cocirculation of respiratory syncytial virus that causes serious respiratory viral illness among children and that frequently circulates during the same time as influenza viruses.[158,159,160] One study assessed rates of influenza-associated hospitalizations among the entire U.S. population during 1979-2001 and calculated an average rate of approximately 108 hospitalizations per 100,000 person-years in children aged <5 years.[48] Two studies have attempted to separate the impact of respiratory syncytial viruses and influenza viruses on rates of hospitalization among children who do not have high-risk conditions.[58,59] Both studies indicated that otherwise healthy children aged <2 years and possibly children aged 2-4 years are at increased risk for influenza-related hospitalization compared with older healthy children ( Table 1 ). Among the Tennessee Medicaid population during 1973-1993, healthy children aged 6 months-2 years had rates of influenza-associated hospitalization comparable with or higher than rates among children aged 3-14 years with high-risk conditions.[58,60] Another Tennessee study indicated a hospitalization rate per year of 3-4/1,000 healthy children aged <2 years for laboratory-confirmed influenza.[36]

The ability of providers to implement the recommendation to vaccinate all children aged 24-59 months during the 2006-07 season, the first year the recommendation will be in place, might vary depending upon vaccine supply (See Influenza Vaccine Supply and Timing of Annual Influenza Vaccination; and

Influenza-associated excess deaths among pregnant women were documented during the pandemics of 1918-19 and 1957-58.[51,161,162,163] Case reports and limited studies also indicate that pregnancy can increase the risk for serious medical complications of influenza.[164,165,166,167,168,169] One study of influenza vaccination of approximately 2,000 pregnant women demonstrated no adverse fetal effects associated with inactivated influenza vaccine;[170] similar results were observed in a study of 252 pregnant women who received inactivated influenza vaccine within 6 months of delivery.[171] No such data exist on the safety of LAIV when administered during pregnancy.

TIV is safe for mothers who are breastfeeding and their infants. Because excretion of LAIV in human milk is unknown and because of the possibility of shedding vaccine virus given the close proximity of a nursing mother and her infant, caution should be exercised if LAIV is administered to nursing mothers. Breastfeeding does not adversely affect the immune response and is not a contraindication for vaccination.

Vaccination is recommended for persons aged 50-64 years because this group has an increased prevalence of persons with high-risk conditions. In 2002, approximately 43.6 million persons in the United States were aged 50-64 years, of whom 13.5 million (34%) had one or more high-risk medical conditions.[172] Influenza vaccine has been recommended for this entire age group to increase the low vaccination levels among persons in this age group with high-risk conditions (see Persons at Increased Risk for Complications). Age-based strategies are more successful in increasing vaccine coverage than patient-selection strategies based on medical conditions. Persons aged 50-64 years without high-risk conditions also receive benefit from vaccination in the form of decreased rates of influenza illness, decreased work absenteeism, and decreased need for medical visits and medication, including antibiotics.[9,10,11,12] Furthermore, 50 years is an age when other preventive services begin and when routine assessment of vaccination and other preventive services has been recommended.[173,174]

Persons who are clinically or asymptomatically infected can transmit influenza virus to persons at high risk for complications from influenza. Decreasing transmission of influenza from caregivers and household contacts to persons at high risk might reduce influenza-related deaths among persons at high risk. In two studies, vaccination of health-care workers was associated with decreased deaths among nursing home patients,[144,145] and hospital-based influenza outbreaks frequently occur where unvaccinated health-care workers are employed. Administration of LAIV has been demonstrated to reduce MAARI in contacts of vaccine recipients[175,176] and to reduce ILI-related economic and medical consequences (such as work days lost and number of health-care provider visits). In addition to health-care workers, additional groups that can transmit influenza to persons at high risk and that should be vaccinated include the following:

  • employees of assisted living and other residences for persons in groups at high risk,

  • persons who provide home care to persons in groups at high risk, and

  • household contacts (including children) of persons in groups at high risk.

In addition, because children aged 0-23 months are at increased risk for influenza-related hospitalization,[58,59,60] vaccination is recommended for their household contacts and out-of-home caregivers, particularly for contacts of children aged 0-5 months, because influenza vaccines have not been approved by FDA for use among children aged <6 months (see Healthy Young Children Aged 6-59 Months).

Healthy persons aged 5-49 years in these groups who are not contacts of severely immunocompromised persons (see Live, Attenuated Influenza Vaccine Recommendations) can receive either LAIV or inactivated influenza vaccine. All other persons in this group should receive inactivated influenza vaccine.

All health-care workers should be vaccinated against influenza annually.[147,177,178] Facilities that employ health-care workers are strongly encouraged to provide vaccine to workers by using approaches that maximize vaccination levels. An improvement in vaccination coverage levels might help to protect health-care workers, their patients, and communities; improve prevention of influenza-associated disease and patient safety; and reduce disease burden. Influenza vaccination levels among health-care workers should be regularly measured and reported. Although vaccination levels for health-care workers are typically <40%, with moderate effort, organized campaigns can attain higher levels of vaccination among this population.[146,179] In 2005, seven states had legislation requiring annual influenza vaccination of health-care workers or the signing of an informed declination,[147] and 15 states had regulations regarding vaccination of health-care workers in long-term-care facilities.[180] Physicians, nurses, and other workers in both hospital and outpatient-care settings, including medical emergency-response workers (e.g., paramedics and emergency medical technicians), should be vaccinated, as should employees of nursing home and chronic-care facilities who have contact with patients or residents.

Limited information is available regarding the frequency and severity of influenza illness or the benefits of influenza vaccination among persons with HIV infection.[181,182] However, a retrospective study of young and middle-aged women enrolled in Tennessee's Medicaid program determined that the risk for cardiopulmonary hospitalizations among women with HIV infection was higher during influenza seasons than during the peri-influenza periods. The risk for hospitalization was higher for HIV-infected women than for women with other well-recognized high-risk conditions, including chronic heart and lung diseases.[183] Another study estimated that the risk for influenza-related death was 9.4-14.6/10,000 persons with acquired immunodeficiency syndrome (AIDS), compared with 0.09-0.10/10,000 among all persons aged 25-54 years and 6.4-7.0/10,000 among persons aged ≥65 years.[184] Other reports indicate that influenza symptoms might be prolonged and the risk for complications from influenza increased for certain HIV-infected persons.[185,186,187]

Vaccination has been demonstrated to produce substantial antibody titers against influenza among vaccinated HIV-infected persons who have minimal AIDS-related symptoms and high CD4+ T-lymphocyte cell counts.[188,189,190,191] A limited, randomized, placebo-controlled trial determined that inactivated influenza vaccine was highly effective in preventing symptomatic, laboratory-confirmed influenza virus infection among HIV-infected persons with a mean of 400 CD4+ T-lymphocyte cells/mm3; a limited number of persons with CD4+ T-lymphocyte cell counts of <200 were included in that study.[192] A nonrandomized study among HIV-infected persons determined that influenza vaccination was most effective among persons with >100 CD4+ cells and among those with <30,000 viral copies of HIV type-1/mL.[187] Among persons who have advanced HIV disease and low CD4+ T-lymphocyte cell counts, inactivated influenza vaccine might not induce protective antibody titers;[190,191] a second dose of vaccine does not improve the immune response in thesepersons.[191,192]

One case study determined that HIV RNA (ribonucleic acid) levels increased transiently in one HIV-infected person after influenza virus infection.[193] Studies have demonstrated a transient (i.e., 2-4 week) increase in replication of HIV-1 in the plasma or peripheral blood mononuclear cells of HIV-infected persons after vaccine administration.[190,194] Other studies using similar laboratory techniques have not documented a substantial increase in the replication of HIV.[195,196,197,198] Deterioration of CD4+ T-lymphocyte cell counts or progression of HIV disease has not been demonstrated among HIV-infected persons after influenza vaccination compared with unvaccinated persons.[191,199] Limited information is available concerning the effect of antiretroviral therapy on increases in HIV RNA levels after either natural influenza virus infection or influenza vaccination.[181,200] Because influenza can result in serious illness and because vaccination with inactivated influenza vaccine might result in the production of protective antibody titers, vaccination might benefit HIV-infected persons, including HIV-infected pregnant women. Therefore, influenza vaccination is recommended.

The risk for exposure to influenza during travel depends on the time of year and destination. In the tropics, influenza can occur throughout the year. In the temperate regions of the Southern Hemisphere, the majority of influenza activity occurs during April-September. In temperate climate zones of the Northern and Southern Hemispheres, travelers also can be exposed to influenza during the summer, especially when traveling as part of large organized tourist groups (e.g., on cruise ships) that include persons from areas of the world where influenza viruses are circulating.[201,202] Persons at high risk for complications of influenza and who were not vaccinated with influenza vaccine during the preceding fall or winter should consider receiving influenza vaccine before travel if they plan to

  • travel to the tropics,

  • travel with organized tourist groups at any time of year, or

  • travel to the Southern Hemisphere during April-September.

No information is available regarding the benefits of revaccinating persons before summer travel who were already vaccinated during the preceding fall. Persons at high risk who received the previous season's vaccine before travel should be revaccinated with the current vaccine the following fall or winter. Persons aged ≥50 years and persons at high risk should consult with their health-care provider before embarking on travel during the summer to discuss the symptoms and risks for influenza and other travel-related diseases.

In addition to the groups for which annual influenza vaccination is recommended, vaccination providers should administer influenza vaccine to any person who wishes to reduce the likelihood of becoming ill with influenza or transmitting influenza to others should they become infected (the vaccine can be administered to children aged ≥6 months), depending on vaccine availability (see Influenza Vaccine Supply and Timing of Annual Influenza Vaccination). A strategy of universal influenza vaccination is being assessed by ACIP.

Persons who provide essential community services should be considered for vaccination to minimize disruption of essential activities during influenza outbreaks. Students or other persons in institutional settings (e.g., those who reside in dormitories) should be encouraged to receive vaccine to minimize the disruption of routine activities during epidemics.[203]


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