Influenza vaccination in children
Author
Caroline Breese Hall, MD Section Editor
Morven S Edwards, MD
George B Mallory, MD Deputy Editor
Mary M Torchia, MD
INTRODUCTION — Influenza is an acute respiratory illness caused by influenza A or B viruses, which occurs in outbreaks worldwide every year, mainly during the winter seasons (in temperate climates).
Certain groups of children are at increased risk of acquiring severe or complicated illness from influenza (show table 1). Among healthy children, influenza generally is an acute, self-limited, and uncomplicated disease. However, it rarely is associated with severe morbidity and mortality. Influenza causes an appreciable disease burden (eg, school and work absence, increased frequency of outpatient medical visits), and children are important vectors for the spread of disease. (See “Clinical features and diagnosis of influenza in children”, section on Epidemiology).
Immunization is the major public health measure for the prevention of influenza infection [1,2] . Influenza vaccination in children will be discussed below. The use of antiviral drugs for the prevention of influenza in children, the design of influenza vaccines, and influenza vaccination in adults are discussed separately. (See “Antiviral drugs for the prevention and treatment of influenza in children” and see “Influenza vaccination in adults”).
INFLUENZA ACTIVITY — The United States Centers for Disease Control and Prevention (CDC), in collaboration with the World Health Organization and its reporting network, tracks influenza virus isolates throughout the world to monitor disease activity and to predict the appropriate components for the annual influenza vaccine. This information, which is updated weekly during influenza season, is available through the CDC’s Web site (www.cdc.gov/flu/weekly).
OVERVIEW — Annual influenza vaccination is the most effective strategy for preventing influenza [1] .
Types of vaccine — Two types of influenza vaccines are licensed for use in the United States:
Trivalent inactivated influenza vaccine (TIV, Fluzone, Fluvirin, Fluarix, FluLaval, Afluria), administered intramuscularly
Trivalent live-attenuated, cold-adapted influenza vaccine (LAIV, FluMist), administered intranasally
A comparison of TIV and LAIV is provided in the table (show table 2).
Composition — The strains included in the vaccine are updated each year to correlate with the strains anticipated to circulate during the coming influenza season.
The World Health Organization and US Food and Drug Administration recommend that influenza vaccines for use in the 2009-2010 influenza season in the northern hemisphere (November to April) contain the following [3,4] :
An A/Brisbane/59/2007 (H1N1)-like virus
An A/Brisbane/10/2007 (H3N2)-like virus
A B/Brisbane/60/2008-like virus
Only the influenza B component represents a change from the 2008-to-2009 northern hemisphere vaccine.
A/Brisbane/59/2007-like virus, A/Brisbane/10/2007-like virus, and B/Florida/4/2006-like virus are contained in the influenza vaccine for the 2009 season in the southern hemisphere (May to October) [5] .
The development of a vaccine to prevent infection with the 2009 novel H1N1 influenza virus (formerly referred to as swine H1N1 influenza virus) that emerged in March 2009 is discussed separately. (See “Prevention of H1N1 influenza A (swine influenza)”, section on Vaccination).
Supply — Information regarding the influenza vaccine supply in the United States is available through the CDC Web site (www.cdc.gov/flu). In the event of a vaccine shortage or delay in distribution, the CDC will provide guidelines for vaccine priority and tiered use of vaccine [1,6] .
Target groups — The CDC’s Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) recommend annual influenza vaccination for all children aged 6 months to 18 years [1,7] . Expansion of the target group to include all children <18 years has the potential to reduce influenza disease, influenza-related medical resource use, and influenza-related school or work absence in this population. In addition, since children are an important reservoir of influenza infection, increasing the numbers of immunized children may reduce influenza among unimmunized contacts within the household and community ("herd immunity") [8-12] . This may be particularly helpful in preventing influenza infection among infants younger than six months and high-risk individuals who did not receive the vaccine. (See "Herd immunity" below). High-risk children — Children and adolescents who are at high risk for severe or complicated influenza infection continue to be a priority (show table 1) [1,7,13-15] . Contacts of high-risk children — The CDC and AAP also recommend influenza immunization for household contacts and out-of-home caregivers of children and adolescents who are at high risk for severe or complicated influenza, including children <59 months of age, and especially infants <6 months of age (show table 1 and show table 2) [1,7] . Immunization of pregnant women during the third trimester of pregnancy appears to protect young infants from laboratory confirmed influenza infection. (See "Immunizations in pregnant women", section on Influenza). Children with high-risk contacts — In addition, influenza vaccine is recommended for children who may transmit influenza to a high-risk household member [1,7] . Others — All other individuals who wish to reduce the risk of becoming ill with influenza or of transmitting influenza to others. Choice of vaccine — The choice of vaccine for an individual child depends upon age and risk factors for severe or complicated influenza [1,7] . TIV is indicated for (www.cdc.gov/flu) [1] : Children 6 to 23 months of age Children (of any age) with asthma and children two to four years of age with a history of recurrent wheezing Children with medical conditions that increase the risk for severe or complicated influenza infection (show table 1) Children who are close contacts of severely immunocompromised individuals (eg, hematopoietic stem cell transplant recipients) (See "Contraindications and precautions for LAIV" below). Children older than two years who are not in one of the categories listed above may receive either TIV or LAIV. Given the potential advantage of broader and more durable immunity with LAIV, we suggest LAIV for such patients if they are not pregnant [16] . (See "LAIV compared to TIV" below). Schedule — Annual immunization is necessary because immunity declines in the year after vaccination [17] . Influenza vaccine should be administered during the fall of each year (October through December in the northern hemisphere) before the onset of influenza season. (See "Epidemiology of influenza", section on Seasonality). The schedule for influenza vaccination varies depending upon the age of the child and prior receipt of influenza vaccine (show table 3 and show algorithm 1) [1] . Two doses of influenza vaccine are necessary for optimal protection in children younger than nine years of age [18-22] . Protection is increased when both doses are administered during the same influenza season [19] . Children ≥ 9 years should receive one dose of influenza vaccine. Children six months through eight years should receive two doses of influenza vaccine in the first year that they are vaccinated; the two doses should be separated by at least four weeks [1] . The two doses may consist of two doses of TIV, two doses of LAIV (if the child is ≥ 2 years of age), or a combination of TIV and LAIV (if the child is ≥ 2 years of age). Children who are between six months and nine years of age and received only one dose of influenza vaccine (either TIV or LAIV) in their first season of vaccination should receive two doses of influenza vaccine during the second season (show algorithm 1) [1,7,23] . However, if it is the third (or later) season and the child received one dose in the first season, even if no influenza vaccine was administered in the intervening year(s), only one dose is required. For children who require two doses of vaccine, the first dose should be administered earlier (ie, September in the northern hemisphere), if the vaccine is available, to ensure that both doses are received before the onset of influenza activity [1,7] . The vaccine should continue to be offered as long into the season as influenza activity occurs [1,24] . Schedule in special circumstances Immune suppression — TIV typically elicits a poor response among children receiving immunosuppressive chemotherapy [24,25] . The optimal time of administration of influenza vaccine in such children is more than three weeks after immunosuppressive chemotherapy has been discontinued, when peripheral granulocyte and lymphocyte counts are >1000/microL.
Glucocorticoids — The antibody response is not affected by brief courses of glucocorticoids or glucocorticoids that are administered every other day [24] . In contrast, the antibody response may be impaired by prolonged administration of glucocorticoids at doses ≥ 2 mg/kg per day or ≥ 20 mg/day.
Influenza vaccination may be deferred in patients receiving high-dose glucocorticoids, as long as deferral does not compromise the likelihood of completion of immunization before the beginning of influenza season. A reasonable approach for influenza prevention in children who are expected to require high-dose glucocorticoids throughout the influenza season would include immunization with TIV, chemoprophylaxis, and immunization of close contacts. (See “Antiviral drugs for the prevention and treatment of influenza in children”).
Travelers — Patients with high-risk conditions who plan to travel to tropical regions should be reminded that influenza occurs throughout the year in the tropics. In addition, summertime outbreaks of influenza have occurred on cruise ships in the northern and southern hemispheres. Repeat vaccination is not necessary in those who received routine vaccination at the appropriate time in the previous fall or winter. (See “Epidemiology of influenza” and see “Immunizations for travel”, section on Influenza).
Herd immunity — Widespread immunization of school and daycare children has appeared to result in “herd immunity” with diminished influenza infection in unvaccinated children and adults of all ages [26] . In one report, as an example, unvaccinated household contacts of vaccinated children had 42 percent fewer febrile respiratory illnesses than unvaccinated household contacts of unvaccinated children; the degree of protection was greater (80 percent reduction) among school-aged household contacts who also had a 70 percent reduction in school days missed [8] .
INACTIVATED VACCINE (TIV) — Intramuscular influenza vaccines are inactivated preparations of either whole virus or subvirion components (“split product”). Split product vaccines cause fewer adverse reactions and are preferred for use in children ≤ 12 years of age. Only split product vaccines are available in the United States (show table 3):
Fluzone for use in children ≥ 6 months of age
Fluvirin for use in children ≥ 4 years of age
Fluarix for individuals ≥ 18 years of age
FluLaval for individuals ≥ 18 years of age
Afluria for individuals ≥ 18 years of age
Efficacy/effectiveness — Because TIV takes approximately nine months to manufacture, it necessarily contains antigens from strains that circulated during the end of the previous season. The protective efficacy of the vaccine is determined largely by the relationship between the strains in the vaccine and viruses that circulate in the outbreak (closeness of “fit”) [27-30] . Estimates of vaccine efficacy also depend upon the activity and severity of circulating influenza viruses, which vary from year to year.
If the “fit” between circulating and vaccine strains is close, rates of protection of 50 to 80 percent against influenza-like illness are expected [27,28,31] . If the fit is poor, as it was during the 2007-2008 influenza season when most of the circulating influenza A (H3N2) and influenza B viruses were suboptimally matched, effectiveness is decreased [32-34] . An interim analysis during the 2007-2008 influenza season indicated an overall effectiveness of 44 percent against laboratory-confirmed influenza [32] .
Laboratory-confirmed influenza — The efficacy of TIV against laboratory-confirmed influenza in healthy children older than two years of age is 59 to 65 percent in meta-analyses [35-37] .
Exposure to influenza infection in previous vaccine years may affect the response to vaccination, especially in children <36 months of age [38] . Children with preexisting hemagglutinin-inhibition antibody to influenza A and influenza B antigen are more likely to develop a protective immune response after immunization.
Families of infants and children susceptible to severe disease from influenza should be reminded that these patients may contract acute influenza infection despite immunization. Such patients may be candidates for antiviral therapy, the efficacy of which is enhanced by early treatment (within 24 hours of onset of symptoms). (See "Antiviral drugs for the prevention and treatment of influenza in children").
Clinical influenza — The effectiveness of TIV in preventing clinical influenza-like illness in children older than two years is 33 to 45 percent in meta-analyses [35-37] . The effectiveness during any given season depends upon the match between the circulating and vaccine strains and the activity and severity of circulating strains.
Prevention of asthma exacerbation — The efficacy of TIV in preventing asthma exacerbations related to influenza infection is uncertain [39,40] . Nonrandomized studies of influenza vaccination in children with asthma have inconsistent results [41,42] . In a randomized trial, 696 children (aged 6 to 18 years) with asthma were randomly assigned to receive TIV or placebo [43] . Pharyngeal cultures were obtained during asthma exacerbations. Reduction in influenza-related asthma exacerbations among vaccine recipients was not demonstrated (risk difference 0.01, 95% CI -0.02 to 0.04).
Otitis media — The efficacy of TIV in the prevention of acute otitis media is discussed separately. (See "Acute otitis media in children: Prevention of recurrence").
Contraindications and precautions for TIV — TIV is contraindicated in children with anaphylactic reactions to chicken or egg proteins because it is prepared in embryonated eggs [1,24] . Similarly, children with sensitivity to thimerosal should not be given vaccine containing thimerosal (show table 3). (See "Allergic reactions to vaccines").
Immunization with TIV usually should be withheld from children with acute febrile illness until their symptoms have resolved. However, minor illnesses with or without fever do not contraindicate use of TIV, particularly among children with upper respiratory tract infection or allergic rhinitis [1,24] .
TIV is safe for mothers who are breastfeeding and their infants [1] .
TIV dose — The dose of TIV varies depending upon the age of the child [1] :
6 to 35 months — 0.25 mL intramuscularly (IM)
≥ 36 months — 0.5 mL IM
Administration with other vaccines — TIV may be administered at the same time, but at a different site, as other recommended immunizations in children [1,24] . (See "Standard childhood immunizations").
Adverse reactions — The most frequent adverse effect of TIV is a local reaction and soreness at the injection site [44-48] . Fever may occur. It is usually low-grade and occurs predominately in children younger than two years; 10 to 35 percent of such children become febrile, usually within 6 to 24 hours after vaccination [37,46-49] .
The safety of TIV was confirmed in a study in which the frequency and cause of medical visits in the two weeks after vaccination of 251,600 children (<18 years) were compared to two control periods [50] . No significant adverse effects or associations were detected in the two weeks after vaccination. A similar study examined the safety of the vaccine in 45,356 children 6 to 23 months of age and likewise found no significant adverse effects in the two weeks after vaccination [51] .
Among the 166 adverse events reported to the United States Vaccine Adverse Event Reporting System (VAERS) between 1990 and 2003 for children younger than two years, fever was most common (35 percent), followed by rash (25 percent), seizure (17 percent; 68 percent of these were associated with fever), and injection site reaction (17 percent) [49] . However, in a large retrospective case-control study, the hazard ratios for these events were not increased during the 42 days after the first dose of TIV among children 6 through 23 months of age [52] .
Immunization of children with asthma has not been associated with asthma exacerbation [39,53] . Immunization in some years has been associated with a slight increase in Guillain-Barré syndrome in adults, but only rare cases have been reported in children. (See "Treatment and prognosis of Guillain-Barré syndrome in adults", section on Influenza vaccine).
The effects of TIV immunization in HIV-infected individuals have been conflicting. Some studies demonstrate a transient increase in the replication of HIV, but these results are inconsistent. Progression of HIV disease or decreased CD4 cell count have not been demonstrated after influenza vaccination [54,55] . Most experts recommend that the potential benefits of immunization outweigh the potential risks. (See "Immunizations in HIV-infected patients", section on Influenza).
Thimerosal — Thimerosal is a mercury-containing anti-bacterial compound that has been used as a preservative in some vaccines. Multidose containers of TIV used in the United States contain approximately 25 microg of mercury per each 0.5 mL dose [1] . "Preservative-free" preparations of Fluvirin and Fluarix may contain trace amounts of mercury (<1 microg per dose), but single-dose preparations of Fluzone and Afluria are thimerosal-free.
A risk related to the small amount of thimerosal in TIV is theoretical and unproven. In comparison to the considerable risk imposed by influenza, the potential benefit of immunization is considered to far outweigh the theoretical risk from a vaccine with a small amount of thimerosal [1,7] . (See "Autism and chronic disease: Little evidence for thimerosal as a contributing factor").
LIVE-ATTENUATED VACCINE (LAIV) — The intranasal influenza vaccine (LAIV, FluMist) is licensed by the United States Food and Drug Administration (FDA) for use in healthy individuals 2 through 49 years of age who are not pregnant (www.cdc.gov/flu) [56,57] .
LAIV is a cold-adapted live-attenuated vaccine prepared through genetic reassortment [45,56,58,59] . The vaccine virus appears to be stable; reversion of the vaccine virus to a virulent strain in vaccinees has not been observed [60,61] . LAIV does not contain thimerosal, but may contain trace amounts of residual egg protein.
Efficacy — The efficacy of LAIV against confirmed influenza among healthy children is approximately 80 percent (95% CI 48-92 percent) in meta-analyses [35,37,57] . Individual studies of LAIV among healthy children have shown an efficacy ranging from 34 to 100 percent, depending primarily upon the closeness of fit between the vaccine strains and the circulating wild type strains [45,62-64] . Efficacy is also affected by the number of doses received [65] .
Some data suggest that LAIV provides protection against influenza types not contained in the vaccine [45,57,66-68] . In a study in which LAIV was administered during consecutive influenza seasons, influenza A/H3N2/Sydney, a strain that was not included in the vaccine, circulated during the second season [62] . The efficacy against culture-positive influenza illness during the first and second seasons were 93 percent (95% CI 88-96 percent) and 87 percent (95% CI 78-93 percent), respectively [69] . The efficacy of LAIV against influenza A/H3N2/Sydney was 86 percent (95% CI 75-92 percent). The increased efficacy/effectiveness of LAIV compared to TIV against mismatched influenza strains has been described in other trials (randomized and nonrandomized) and meta-analyses [45,57,68] .
LAIV compared to TIV — According to several studies, LAIV may be more efficacious than TIV, may provide greater immunity against mismatched strains (as described above), and may provide immediate protection during an outbreak, as illustrated below [45,53,57,68,70]
In a Phase 3 study comparing TIV and LAIV in 8475 children 6 to 59 months of age during the 2004-2005 influenza season, fewer cases of culture-confirmed influenza occurred in the group receiving LAIV than TIV (attack rates of 3.9 and 8.6 percent, respectively) [45] . LAIV was significantly more protective against both well-matched and mismatched influenza A viruses, but not influenza B viruses.
Influenza attack rates among asthmatic children ages 6 to 17 years who received LAIV were lower than among those who received TIV (4.1 versus 6.2 percent) [53] .
Influenza attack rates among children ages 6 to 71 months with recurrent respiratory tract infections who received LAIV were lower than among those who received TIV (2.3 versus 4.8 percent) [70] .
During an outbreak in which the circulating and vaccine strains of influenza A (H3N2) differed, LAIV was 37 percent effective against influenza-positive illness, whereas TIV did not provide protection [68] . Protection with LAIV was similar within 14 days of immunization and >14 days after immunization, suggesting that LAIV provides protection through both innate and adaptive mechanisms.
Although LAIV is more expensive than TIV, its relative increased efficacy may result in decreased health-care and societal costs for children 24 to 59 months of age [57,71] .
Contraindications and precautions for LAIV — Contraindications to LAIV include (www.cdc.gov/flu) [56] :
Age <2 years History of anaphylactic reaction to egg or chicken protein, gentamicin, gelatin, or arginine Long-term aspirin or salicylate therapy Known or suspected immunodeficiency History of Guillain-Barré syndrome Asthma Recurrent wheezing in children younger than five years Other conditions considered to be risk factors for severe influenza infection or complications of influenza infection, including: - Chronic pulmonary disorders (including asthma) - Cardiac disorders (excluding hypertension) - Pregnancy - Chronic metabolic disease - Renal dysfunction - Hemoglobinopathies - Immunodeficiency or immunosuppressive therapy TIV is preferred to LAIV for contacts of severely immunocompromised individuals (eg, hematopoietic stem cell transplant recipients) [56] . Contacts of individuals with lesser degrees of immunocompromise (eg, persons with diabetes, asthma or HIV infection, those who are receiving corticosteroids) may receive either TIV or LAIV vaccine [56] . Health-care workers who receive LAIV should refrain from contact with severely immunocompromised individuals for seven days [56,72] . LAIV can be administered to children with minor acute illnesses, with or without fever. Clinical judgment should be used before administering the vaccine to children with nasal congestion of such severity that it may impede delivery of the vaccine to the nasopharyngeal mucosa. Administration of the vaccine may be deferred until resolution of illness unless deferral of vaccination may result in the child not being vaccinated [56] . If the child sneezes after LAIV is administered the dose should not be repeated [56] . Breastfeeding does not adversely affect the immune response to LAIV and is not a contraindication to LAIV [56,73] . LAIV dose — The dose for LAIV is 0.2 mL administered intranasally (0.1 mL to each nostril) [56] . Administration with other vaccines — LAIV can be administered at the same time as other live and inactivated vaccines [74] . However, if it is not administered on the same day as other live vaccines (eg, measles-mumps-rubella, varicella zoster), it should be administered at least four weeks later [56] . Adverse effects — LAIV appears to be safe [45,53,57,75] . Few adverse events occurred in prelicensure controlled trials in healthy children 12 months to 18 years of age [57,62,76,77] , and no statistically significant differences were observed between placebo and LAIV recipients in rates of fever, rhinitis, or nasal congestion [56,73] . In a study of the effectiveness of a school-based immunization program, students who received LAIV had significantly higher rates of symptoms of influenza-like illness (other than wheezing) and use of nonprescription medicines in the week after immunization than in the week before immunization [11] . However, there were no significant increases in the use of prescription medications, visits to doctors or clinics, or school days lost by the vaccinated students. During the first two seasons after licensure, approximately 2.5 million individuals received LAIV [78] . No unexpected serious events were identified although a small number of serious adverse events were reported to VAERS: possible anaphylaxis (7), Guillain-Barré syndrome (2), Bell's palsy (1), and asthma exacerbation among individuals with a history of asthma (8) [78] . Asthma and wheezing — Studies evaluating the association between LAIV and asthma, wheezing, or respiratory illness have had conflicting results [45,53,70,75,77,79] . Among older children, receipt of LAIV has not been associated with an increased frequency of wheezing or asthma-related events [53,75,77] . Prelicensure studies identified a possible association between LAIV and episodes of wheezing among children younger than five years of age [75,77] . In one of these trials, which took place over four years and did not exclude children with intermittent wheezing, the association was only noted during the first year [75] . Subgroup analysis found no increased risk of medically attended acute respiratory illnesses, including asthma exacerbation, among LAIV recipients with a history of intermittent wheezing during the 42 days after vaccination [79] . A subsequent randomized trial comparing LAIV and TIV among children 6 to 59 months without asthma or history of recent wheezing (ie, with the 42 days before vaccination) failed to confirm an association between LAIV and wheezing for children >24 months [45] . However, among children <24 months, medically significant wheezing within 42 days after vaccination was more frequent among LAIV recipients (2.3 versus 1.5 percent), particularly among those 6 to 11 months of age (3.8 versus 2.1 percent). The proportion of children who had wheezing episodes after vaccination who had subsequent episodes of wheezing was similar between groups (32 versus 28 percent for one subsequent episode and 4 versus 5 percent for two or more subsequent episodes in the LAIV and TIV groups, respectively). In post-hoc analyses, rates of hospitalization within 180 days of vaccination were significantly higher among 6- to 11-month-old recipients of LAIV than among 6- to 11-month-old TIV recipients (6.1 versus 2.6 percent) [45] . Higher (but not significantly higher) rates of hospitalization also were observed in children 12 to 47 months of age who had a history of wheezing before entering the study. LAIV is not licensed for use in children younger than two years, nor in children with asthma or risk factors for serious influenza disease. Until additional data are available, the above observations suggest that TIV should continue to be used for children 6 to 24 months of age and young children with a history of wheezing. Viral shedding — Viral shedding after immunization with LAIV was evaluated in 344 subjects divided into three groups (5 to 8 years, 9 to 17 years, and 18 to 49 years), with the following observations [72] : 5 to 8 years — Viral shedding occurred in 44 percent, peaked on days 2 to 3, and resolved by 10 days 9 to 17 years — Viral shedding occurred in 27 percent, peaked on days 2 to 3, and resolved by 6 days 19 to 49 years — Viral shedding occurred in 17 percent, peaked on days 2 to 3, and resolved by 6 days Transmission — Transmission of the attenuated influenza strains to unprotected contacts appears to be uncommon, possibly because only low titers of vaccine virus are shed [80] . In a study in which 197 daycare attendees (aged 9 to 36 months) were randomly assigned to receive LAIV or placebo, 80 percent of LAIV recipients shed at least one vaccine strain [80] . There was one confirmed case of transmission of a vaccine strain to a placebo recipient who did not develop clinically significant illness. The calculated probability of transmission to a child after contact with a single vaccinated child was 0.58 percent (95% CI 0-1.7 percent). Whether LAIV is secreted in human milk is unknown [56] . INFORMATION FOR PATIENTS — Educational materials on this topic are available for patients. We encourage you to print or e-mail these topics, or to refer patients to our public Web site www.uptodate.com/patients, which includes these and other topics. (See "Patient information: Childhood immunizations" and see "Patient information: Immunizations for infants and children age 0 to 6 years"). SUMMARY AND RECOMMENDATIONS Influenza virus infection is associated with increased rates of hospitalization in children with risk factors for severe or complicated influenza infection, and in otherwise healthy children younger than five years, particularly those younger than two years (show table 4). (See "Clinical features and diagnosis of influenza in children", section on Risk factors). Immunization is the major means of influenza prevention. Two types of influenza vaccines are available: inactivated vaccine (TIV), which is administered intramuscularly, and live-attenuated, cold-adapted influenza vaccine (LAIV), which is administered intranasally (show table 2 and show table 3). (See "Types of vaccine" above). In accordance with the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP), we recommend annual influenza immunization for (Grade 1A) (See "Target groups" above): - Children aged 6 months through 18 years. Children and adolescents who are at risk for severe or complicated influenza (show table 4) are a priority. (See "Target groups" above). - Household contacts and out-of-home caregivers of children 0 to 59 months of age and other individuals who are at increased risk of severe or complicated influenza infection (show table 4). Pending an adequate supply of influenza vaccine, we also recommend annual influenza vaccination for individuals who do not belong to a high-risk group but who wish to avoid influenza infection (Grade 1A). The choice of vaccine for an individual child depends upon age and risk factors for severe or complicated influenza. TIV is indicated for: - Children 6 to 23 months of age - Children (of any age) with asthma and children two to four years of age with a history of recurrent wheezing - Children with medical conditions that increase the risk for severe or complicated influenza infection (show table 4) - Children who are close contacts of severely immunocompromised individuals (eg, hematopoietic stem cell transplant recipients) (See "Choice of vaccine" above and see "Contraindications and precautions for LAIV" above). Individuals older than two years who are not among of the categories listed above may receive either TIV or LAIV. Given the potential advantage of broader and more durable immunity with LAIV, we suggest LAIV for such patients if they are not pregnant (Grade 2A). (See "LAIV compared to TIV" above). Annual immunization is necessary because immunity declines during the year following vaccination. Immunization should be administered in the fall. (See "Schedule" above). The vaccine schedule varies depending upon age and prior history of influenza immunization (show algorithm 2). The dose of TIV varies depending upon age. (See "Schedule" above and see "TIV dose" above). Use of UpToDate is subject to the Subscription and License Agreement . REFERENCES 1 Fiore, AE, Shay, DK, Broder, K, et al. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008. MMWR Recomm Rep 2008; 57:1. 2 Guidance on the use of oseltamivir and amantadine for the prophylaxis of influenza. Technology Appraisal No. 67. National Institute for Clinical Excellence London, 2003. Available at www.nice.org.uk. Accessed on August 7, 2008. 3 World Health Organization. Recommended composition of influenza virus vaccines for use in the 2009-2010 northern hemisphere influenza season. 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Pediatr Infect Dis J 2008; :. 80 Vesikari, T, Karvonen, A, Korhonen, T, et al. A randomized, double-blind study of the safety, transmissibility and phenotypic and genotypic stability of cold-adapted influenza virus vaccine. Pediatr Infect Dis J 2006; 25:590. ©2009 UpToDate® • customerservice@uptodate.com www.uptodate.com Leumit Health Services(Kupat Cholim)-Simply the best medical care in Ramat Beit Shemesh