Prophylactic effect of inactivated influenza vaccine on young children

BACKGROUND: The effectiveness of inactivated influenza vaccine in healthy infants and young children has been controversial. The aim of this study was to determine the prophylactic effect of inactivated influenza vaccine in young children. METHODS: Eighty-six healthy infants and children younger than 7-years-old were immunized by a subcutaneous injection of inactivated influenza vaccine before the 1999/2000 influenza season. Ninety-four age-matched children were randomly assigned as the control. These children were followed-up from January to April, 2000. A diagnosis of influenza A virus infection was made rapidly by a positive result of the the enzyme immunoassay membrane test using enzyme-conjugated monoclonal antibodies specific for a conserved epitope of influenza A nucleoprotein. The incidence of influenza A infection was compared and statistically assessed. RESULTS: The prevalence of influenza A virus infection, diagnosed by the influenza A rapid detection test, was 5.8% in the vaccine group and 17.0% in the control group, that is significantly lower in the vaccine receiving group than the non-receiving group (P = 0.016). However, four out of five infected children in the vaccine group were younger than 2-years-old. CONCLUSION: We conclude that inactivated influenza vaccine reduces the incidence of influenza A virus infection in 2-6-year-old children.     

Clinical and immunologic effects following oral immunization against influenza in children in day care and infection susceptible young children

57 infants and small children (9 months - 3.1 years) were orally immunized by an inactivated influenza vaccine (Mississippi 1/85; dosage: 110 micrograms HA); the control group (n = 15) received placebo. After three months the influenza specific Ig-concentrations of serum and secretions demonstrated a controverse course: Specific IgG (serum) decreased and specific IgA (nasale secretions) increased statistically significant (p less than 0.025), especially in children suffering from frequently relapsing respiratory infections (n = 31). Moreover the immunized children had also a better clinical outcome in the following 3 months: the number of days with cough, febrile symptoms and the antibiotics therapy were significantly decreased. Recommendations are given for an improvement of the orale influenza vaccine and its indicated administration in small children.     

Influenza burden in febrile infants and young children in a pediatric emergency department

BACKGROUND: In France, epidemiologic data in children in ambulatory settings are scarce. We aimed to measure the burden of influenza in young children. METHODS: Febrile children younger than 36 months were consecutively recruited in a pediatric emergency department during the 2002 epidemic peak. Virology analysis and follow-up were systematic. RESULTS: During calendar weeks 3 to 6, 2002, 575 children were recruited; 49% were positive: A/H3N2 in 44% and B in 5%. Prevalence rate was 57% in 12- to 35-month-old children and 39% in infants younger than 12 months. The main clinical pictures were nonrespiratory in one third of them. One of 8 patients had a complication. One of 10 patients was hospitalized, and the estimated specific hospitalization rate for the study period was 237 of 100,000 in the general population among infants younger than 12 months. Forty-two percent of children (n = 110) were prescribed antibiotics and at least 34% of them were inappropriate (n = 89). Median length of disease was 8 days, and 25% of the children had not fully recovered by day 11. Only one child had been previously vaccinated of 65 with chronic conditions. Both epidemic strains were covered by the vaccine. CONCLUSIONS: Health outcomes showed that influenza disease burden in young French children is similar to that observed in North America. An active vaccination strategy would have strongly reduced the burden of influenza and lowered antibiotic use. Continuous efforts are needed to reach requirements of our influenza vaccination policy.     

Superior relative efficacy of live attenuated influenza vaccine compared with inactivated influenza vaccine in young children with recurrent respiratory tract infections

BACKGROUND: Young children have a high incidence of influenza and influenza-related complications. This study compared the efficacy and safety of cold-adapted influenza vaccine, trivalent (CAIV-T) with trivalent inactivated influenza vaccine (TIV) in young children with a history of recurrent respiratory tract infections (RTIs). METHODS: Children 6 to 71 months of age were randomized to receive 2 doses of CAIV-T (n = 1101) or TIV (n = 1086), 35 +/- 7 days apart before the start of the 2002-2003 influenza season and were followed up for culture-confirmed influenza, effectiveness outcomes, reactogenicity, and adverse events. RESULTS: Overall, 52.7% (95% confidence interval [CI] = 21.6%-72.2%) fewer cases of influenza caused by virus strains antigenically similar to vaccine were observed in CAIV-T than in TIV recipients. Greater relative efficacy for CAIV-T was observed for the antigenically similar A/H1N1 (100.0%; 95% CI = 42.3%-100.0%) and B (68.0%; 95% CI = 37.3%-84.8%) strains but not for the antigenically similar A/H3N2 strains (-97.1%; 95% CI = -540.2% to 31.5%). Relative to TIV, CAIV-T reduced the number of RTI-related healthcare provider visits by 8.9% (90% CI = 1.5%-15.8%) and missed days of school, kindergarten, or day care by 16.2% (90% CI = 10.4%-21.6%). Rhinitis and rhinorrhea, otitis media, and decreased appetite were the only events that were reported more frequently in CAIV-T subjects. There was no difference between groups in the incidence of wheezing after vaccination. CONCLUSIONS: CAIV-T was well tolerated in these children with RTIs and demonstrated superior relative efficacy compared with TIV in preventing influenza illness.     

Effect of rapid diagnosis of influenza virus type a on the emergency department management of febrile infants and toddlers.

BACKGROUND: Evidence shows that the rapid detection of influenza using an enzyme-linked immunosorbent assay decreases antibiotic use in the treatment of pediatric patients. To our knowledge, the effect on other diagnostic testing in an emergency department (ED) has not been examined. OBJECTIVE: To determine the effect of rapid diagnosis of influenza virus type A on the clinical management of febrile infants and toddlers in a pediatric ED at an urban children's hospital. MATERIALS AND METHODS: A retrospective review of ED records from an electronic database was performed. All children 2 to 24 months of age, with a temperature higher than 39 degrees C who had a positive influenza virus type A test result using an enzyme-linked immunosorbent assay from November 1, 1998, through April 30, 2000 (n = 72), were included in this study. Two groups were compared-those who had positive test results reported before discharge from the ED (early diagnosis) and those who had positive test results after discharge (late diagnosis). RESULTS: Forty-seven patients (65%) were in the early diagnosis group and 25 (35%) in the late diagnosis group. The groups were similar for age, temperature, and triage category. Fewer patients in the early diagnosis group received ceftriaxone sodium compared with those in the late diagnosis group (2% vs 24%, P =.006); there were fewer urinalyses (2% vs 24%, P =.006) and complete blood cell counts performed (17% vs 44%, P =.02). CONCLUSIONS: Rapid confirmation of influenza virus type A infection seems to decrease ancillary tests and antibiotic use in febrile infants and toddlers in the ED. A prospective study with a larger group is needed to confirm these findings.     

Role of hepatitis B immunoglobulin in infants born to hepatitis B e antigen-negative carrier mothers in Taiwan

BACKGROUND: The efficacy of hepatitis B immunoglobulin (HBIG) in infants of hepatitis B e antigen (HBeAg)-negative hepatitis B surface antigen (HBsAg) carrier mothers in Taiwan is not clear. OBJECTIVE: To describe the responses of infants born to HBeAg-negative carrier mothers receiving HBIG combined with hepatitis B vaccine. METHODS: Term babies born to HBeAg-negative carrier mothers were assigned based on chart number to 1 of the 2 treatment groups. Group A infants (n = 94) received 0.5 ml (145 IU) of HBIG within 24 h of birth and 3 subsequent doses of recombinant hepatitis B virus (HBV) vaccine at 3 to 5 days, 1 month and 6 months of age. Group B infants (n = 122) received 3 doses of vaccines only. Infants (n = 19) born to HBeAg-positive carrier mothers were treated like those in Group A and are referred to as Group C. Sera obtained from infants at 2 and 7 months of age were tested for hepatitis B virus (HBV) markers. RESULTS: There were 2 (1%; one in Group A and one in Group B) subclinical breakthrough hepatitis B infections among studied infants. One (5%) child of Group C had asymptomatic HBV infection at the age of 7 months and became a chronic carrier. The rate of protective anti-hepatitis B surface antibody (anti-HBs) titers achieved (>10 mIU/ml) by 2 months of age was significantly higher in Group A than that in Group B (98% vs. 57%, P < 0.001). However, it was not different by 7 months of age. Infants (Group A) immunized with HBIG and vaccine had a significantly higher geometric mean titer (GMT, milli-International Units/ml) of anti-HBs than those (Group B) with vaccines only at 2 months of age (P < 0.001). Conversely at 7 months of age, the GMT of anti-HBs was significantly higher in infants who received vaccine only (P = 0.001). CONCLUSIONS: A protective level of antibodies was achieved earlier in those infants receiving both passive and active immunizations. However, infants receiving active immunizations alone achieved a higher GMT at 7 months of age. There was no clear benefit of passive-active vs.active immunization alone for chronic HBV infection in infants of HBsAg-positive, HBeAg-negative mothers.     

Safety and immunogenicity of a paediatric presentation of an influenza vaccine.

BACKGROUND: Flu vaccination in otherwise healthy infants and young children is important to prevent severe disease, as well as to control epidemic spread of influenza infection. AIMS: To examine the safety and immunogenicity of a paediatric presentation of a purified, inactivated, triton split influenza vaccine. METHODS: Two doses of the vaccine, provided in prefilled syringes of 0.25 ml, were administered, one month apart, to 67 children under 3 years of age. RESULTS: Nine cases of immediate reaction to vaccination (macules/papules) were observed after the second injection only. During the study period, 9% of children experienced at least one delayed local reaction, and 28% of children presented at least one systemic reaction. Almost all reactions were mild and transient. Immunogenicity results surpassed the European Community recommendations for a 0.50 ml dose of vaccine in adults. CONCLUSION: This paediatric formulation of inactivated flu vaccine appears safe and immunogenic in children from 6 months to 3 years of age; the convenient presentation in a prefilled syringe of 0.25 ml volume will facilitate administration of the dose recommended for young children.     

Assessment of the immune response to trivalent split influenza vaccine in children with solid tumors

PURPOSE: To assess the immune response to influenza vaccine in children with solid tumors receiving chemotherapy or under the influence of chemotherapy. METHODS: Forty-five children (aged 1-18) with solid tumors on chemotherapy or within 6 months of completion of chemotherapy were included in the study. The children received two doses of intramuscular trivalent split influenza vaccine with 1 month apart in November-December 2003 (children <4 age 0.25 ml; >4 age 0.5 ml). Antibody titer was detected in the pre-vaccination and 4-week post-vaccination sera by hemagglutination inhibition (HI) method. Immune responses were measured as protective, geometric mean titers (GMT), and fourfold rises in HI titers. RESULTS: We revealed that the post-vaccination GMT for each of the three antigens in patients with solid tumors has increased significantly (P < 0.05). A fourfold rise in the percentage of post-vaccination antibody titers has been detected as 84.4% for H(1)N(1), 77.8% for H(3)N(2), 60% for B. Stratification of patients as on active chemotherapy or being within 6 months of completion of chemotherapy in terms of fourfold rise in antibody titers exposed a statistically significant difference for only B (P = 0.34). Post-vaccination protective rates were between 86 and 97%. CONCLUSIONS: Due to the interruptions in treatment caused by influenza infections, and economic benefits of the vaccine, we suggest that inactivated influenza vaccine should be applied as two doses annually in patients with solid tumor.     

Live attenuated influenza vaccine induces cross-reactive antibody responses in children against an a/Fujian/411/2002-like H3N2 antigenic variant strain

Serum antibody titers against the A/Panama/2007/99(H3N2) and A/Fujian/411/2002(H3N2)-like viruses were determined in children 6-35 months of age who received either 1 dose of the inactivated influenza vaccine or the live attenuated influenza vaccine containing the A/Panama strain. Results indicated that the live vaccine induced higher antibody responses than the inactivated vaccine against the A/Panama and A/Fujian-like viruses.     

Impact of the conjugate pneumococcal vaccine in arkansas

BACKGROUND: On the basis of the success of the early trials in the prevention of invasive pneumococcal disease in infants and children using a heptavalent conjugate pneumococcal vaccine, the American Academy of Pediatrics recommended in August 2000 that the vaccine be given concurrently with other childhood immunizations. METHODS: Data concerning invasive pneumococcal infections from 1998-2000 were compared with 2001-2003 to assess the impact of the heptavalent pneumococcal conjugate vaccine in Arkansas. Basic demographic data were gathered as well as history of vaccination with the pneumococcal vaccine, underlying medical conditions, site of infection and morbidity and mortality. Pneumococcal isolates were serogrouped or serotyped and penicillin susceptibilities were obtained. RESULTS: The incidence of invasive disease decreased from a high of 5.78/100,000 population to 3.02/100,000 population (P = 0.002). Although the percentage of White patients increased from 2001-2003, the overall incidence of disease did not change. The incidence of disease among Blacks fell from 20.5/100,000 population to 4.9/100,000 population. The greatest decrease of disease occurred in children 24 months of age or younger with the incidence rate falling from 44.2/100,00 population to 8.30/100,000 population (P < 0.02). The incidence among White children 24 months of age or younger fell from 19/100,000 population to 1.8/100,000 population, whereas that of Black children 24 months of age or younger declined from 164/100,000 to 35/100,000.From 1998 to 2000, 3.7/100 cases were from nonvaccine serogroups compared with 44/100 cases from 2001 to 2003 (P < 0.001). In children 24 months of age or younger, the number of nonvaccine isolates increased from 1.3/100 cases to 30.5/100 cases (P < 0.001). Overall 56 (44%) were nonsusceptible to penicillin from 1998 to 2000; that was not significantly different from 2001-2003 when 37 (46%) of 81 isolates were nonsusceptible to penicillin. CONCLUSIONS: A significant decrease of invasive pneumococcal disease has been documented in Arkansas. Of concern, however, is the increasing number of invasive isolates not included in the current vaccine.     

Lower respiratory tract infections associated with influenza A and B viruses in an area with a high prevalence of pediatric human immunodeficiency type 1 infection

BACKGROUND: Despite the high burden of pediatric HIV-1 infection in developing countries, there are few data on the clinical course of influenza virus-associated lower respiratory tract infection (LRTI) in these children. OBJECTIVE: To define and compare the clinical course of HIV-1-infected and -uninfected African children hospitalized with influenza virus associated severe LRTI. METHODS: Children with severe LRTI were prospectively recruited between March, 1997, and March, 1999, as part of a broader study evaluating the etiology and outcome of this condition in hospitalized HIV-1-infected and -uninfected children. The results of children in whom influenza A or B virus was identified by immunofluorescent antibody staining after shell vial culture are reported. Viruses isolated were typed by hemagglutination inhibition assays. RESULTS: Twenty-five (21.6%) of the 116 children hospitalized with severe LRTI in whom influenza A or B virus was identified were HIV-1-infected. HIV-1-infected children were older than uninfected children (mean age +/- SD 17.4 +/- 10.8 months vs. 10.2 +/- 8.9 months; P = 0.002). HIV-1-infected children were more likely to have an underlying medical illness (in addition to HIV-1 infection) predisposing them to more severe LRTI (32.0% vs. 13.2%; P = 0.03). HIV-infected children were also more likely to have indirect evidence of bacterial coinfection, including chest radiographic evidence of confluent alveolar consolidation (78.9% vs. 35.1%, P = 0.006), and were less likely be wheezing (8.0% vs. 31.9%, P = 0.01). However, there was no difference in the clinical outcome of HIV-1-infected and -uninfected children. The duration of hospitalization [median (range) 5 (2 to 33) days vs. 4 (0 to 21) days, P = 0.08] and the mortality rates (8.0% vs. 2.2%, P = 0.20) were similar between HWV-1-infected and -uninfected children. CONCLUSION: HIV-1-infected children hospitalized with severe LRTI associated with influenza virus have an outcome similar to that of HIV-1-uninfected children even in the absence of antiretroviral or anti-influenza virus treatment.     

Immune response after influenza vaccination in children with cancer

PURPOSE: To assess the immune response to inactivated trivalent split influenza vaccine in children with cancer. PROCEDURES: Forty-four children with various types of malignancies received two doses of influenza vaccine 2-4 weeks apart. Hemagglutinin-inhibition (HI) antibody titers were determined in paired sera obtained just before the first vaccination and 4 weeks after the second vaccination. RESULTS: Influenza vaccine was administered to all children without any serious adverse effects. Protective titer rates (proportion of patients achieving antibody titers > or =40 among those with pre-vaccination titers <40) and response rates (proportion of patients with fourfold or more antibody rise) were 72% and 65% for H1N1, 60% and 40% for H3N2, and 38% and 46% for influenza B, respectively. However, patients on chemotherapy showed a significantly lower immune response to influenza A than those having completed chemotherapy; protection titer rates were 42% versus 90% for H1N1 (P = 0.006) and 25% versus 83% for H3N2 (P = 0.019). For influenza B, patients with low IgG showed a lower response rate than those with high IgG (29% vs. 61%, P = 0.040). Multivariate analysis revealed that factors significantly associated with a lower immune response were low IgG (P < 0.001) and administration of chemotherapy (P = 0.003) for H1N1, administration of chemotherapy (P = 0.008) for H3N2, and low white blood cell (WBC) count (P = 0.030) and low IgG (P = 0.030) for influenza B. CONCLUSIONS: Influenza vaccination given to children with cancer was safe and induced immune reaction comparable to healthy children, although patients on chemotherapy and/or with chemotherapy-related conditions had a limited ability to produce a sufficient immune response.     

Recommendations for influenza immunization of children

Epidemiologic studies indicate that children of all ages with certain chronic conditions and otherwise healthy children younger than 24 months of age are hospitalized for influenza infection and its complications at high rates similar to those experienced by the elderly. Annual influenza immunization is recommended for all children with high-risk conditions who are 6 months of age and older. Young, healthy children are at high risk of hospitalization for influenza infection; therefore, the American Academy of Pediatrics recommends influenza immunization for healthy children 6 through 24 months of age, for household contacts and out-of-home caregivers of all children younger than 24 months of age, and for health care professionals. To protect these children more fully against the complications of influenza, increased efforts are needed to identify all high-risk children and inform their parents when annual immunization is due. The purposes of this statement are to update recommendations for routine use of influenza vaccine in children and to review the indications for use of trivalent inactivated influenza vaccine and live-attenuated influenza vaccine.     

Comparison of immunogenicity and tolerability of a virosome-adjuvanted and a split influenza vaccine in children

OBJECTIVE: To compare the immunogenicity and safety of a virosome-adjuvanted influenza vaccine (Inflexal V; Berna Biotech, Berne, Switzerland) and a split influenza vaccine (Fluarix; GlaxoSmithKline Biologicals, Rixensart, Belgium) in children. SUBJECTS AND METHODS: The subjects, 453 children ages 6 to 71 months, were stratified into primed and unprimed and age groups (6 to 35 and 36 to 71 months) and then randomized 1:1 to receive virosome-adjuvanted (n = 224) or split influenza vaccine (n = 229), a half or full dose was given intramuscularly according to age. Unprimed children received a second dose after 4 weeks. Blood samples (n = 326) collected pre-and 28 days postvaccination were analyzed by hemagglutination inhibition test. Safety assessments were made at baseline and follow-up visits by the investigators and by parents for the 4 days after vaccinations. RESULTS: Both vaccines induced an effective immune response. Seroconversion rates (>4-fold titer rise) against the WHO recommended strains A/New Caledonia (H3N2), A/Moscow (H1N1) and B/Hongkong (B) were 80.1, 66.0 and 90.4% for the virosome-adjuvanted and 75.9, 62.9 and 89.4% for the split influenza vaccine, respectively. Unprimed children's seroconversion rates for H3N2 were significantly higher (P = 0.02) for the virosome-adjuvanted (88.8%) than for split influenza vaccine (77.5%). Seroprotection rates (titer of > 40) for H3N2, H1N1 and B, respectively, were 87.8, 80.1 and 90.4% after vaccination with the virosome-adjuvanted vaccine and 82.9, 78.2 and 89.4% after the split influenza vaccine. Unprimed children's seroprotection rate was significantly higher (P = 0.03) for H3N2 after the virosome-adjuvanted (88.8%) than those for the split influenza vaccine (78.3%). Equivalent geometric mean titer fold increases were evident for both vaccines. No serious adverse events were seen. Pain/ tenderness, redness and swelling/induration was found in 25.4, 11.2 and 8.9% for the virosome-adjuvanted vaccine and in 24.0, 9.2 and 6.1% for the split influenza vaccine, respectively. The rates of fever, malaise/irritability and shivering was 6.3, 11.6 and 2.7% for the virosome-adjuvanted vaccine and 8.3, 11.8 and 2.6% for the split influenza vaccine, respectively. CONCLUSIONS: The virosome-adjuvanted influenza vaccine showed greater immunogenicity over the split influenza vaccine in unprimed children and showed a trend toward better immunogenicity in the rest of the study population. Both vaccines were well-tolerated.     

Comparison of influenza A and influenza B virus infection in hospitalized children

BACKGROUND: Influenza A and B viruses were cocirculating in Australia in the winter of 1997. Objective: To compare the clinical and demographic features of children with influenza A or influenza B virus infection admitted to a paediatric tertiary referral centre. METHODOLOGY: Retrospective chart review of 91 hospitalized children with culture-proven influenza A or B virus infection during 1997. RESULTS: Thirty-six (56%) of 64 children with influenza A were under 12 months of age compared with seven (26%) of 27 children with influenza B virus infection (P = 0.02). Influenza B virus infection was more common in children with underlying medical problems (P = 0. 01). Neurological manifestations were present in eight (12.5%) of 64 children with influenza A and none with influenza B virus infection (P = 0.09). There were no significant differences in signs and symptoms of children with influenza A and B virus infection, in severity of illness or in duration of hospital stay. CONCLUSIONS: A greater proportion of children admitted with influenza A virus infection were under 12 months of age. Influenza B virus infection is associated more commonly with underlying medical disorders. It is not possible to differentiate between influenza A or B virus infection from presenting clinical signs and symptoms.     

Comparison of the efficacy and safety of live attenuated cold-adapted influenza vaccine, trivalent, with trivalent inactivated influenza virus vaccine in children and adolescents with asthma

BACKGROUND: Despite their potential for increased morbidity, 75% to 90% of asthmatic children do not receive influenza vaccination. Live attenuated influenza vaccine (LAIV), a cold-adapted, temperature-sensitive, trivalent influenza vaccine, is approved for prevention of influenza in healthy children 5 to 19 years of age. LAIV has been studied in only a small number of children with asthma. METHODS: Children 6 to 17 years of age, with a clinical diagnosis of asthma, received a single dose of either intranasal CAIV-T (an investigational refrigerator-stable formulation of LAIV; n = 1114) or injectable trivalent inactivated influenza vaccine (TIV; n = 1115) in this randomized, open-label study during the 2002-2003 influenza season. Participants were followed up for culture-confirmed influenza illness, respiratory outcome, and safety. RESULTS: The incidence of community-acquired culture-confirmed influenza illness was 4.1% (CAIV-T) versus 6.2% (TIV), demonstrating a significantly greater relative efficacy of CAIV-T versus TIV of 34.7% (90% confidence interval [CI] 9.4%-53.2%; 95% CI = 3.9%-56.0%). There were no significant differences between treatment groups in the incidence of asthma exacerbations, mean peak expiratory flow rate findings, asthma symptom scores, or nighttime awakening scores. The incidence of runny nose/nasal congestion was higher for CAIV-T (66.2%) than TIV (52.5%) recipients. Approximately 70% of TIV recipients reported injection site reactions. CONCLUSIONS: CAIV-T was well tolerated in children and adolescents with asthma. There was no evidence of a significant increase in adverse pulmonary outcomes for CAIV-T compared with TIV. CAIV-T had a significantly greater relative efficacy of 35% compared with TIV in this high-risk population.     

Antibody responses after inactivated influenza vaccine in young children

BACKGROUND: The frequency and duration of antibody responses after trivalent inactivated influenza vaccine (TIV) in young children are not well defined and assume greater importance with the expanded recommendations for vaccine use in children aged 6 months-5 years. METHODS: Forty-three children aged 6-23 months were vaccinated with TIV in the fall of 2002. At enrollment the majority of children were seronegative to one or more of the vaccine antigens and had no previously documented influenza. Postvaccination sera were collected in the subsequent fall and winter seasons. Acute antibody responses to TIV were determined using standardized hemagglutination inhibition (HAI) and neutralization assays. In calculating the duration of responses, sequential sera were analyzed to the last available sera, to the point at which antibody became undetectable, or to intercurrent influenza infection. RESULTS: Forty-three subjects contributed 121 sera that were analyzed for HAI responses to TIV. Four-fold HAI rises after 2 doses of TIV in naive individuals were seen in 13 (72%) to H3N2, 22 (92%) to H1N1, and 15 (60%) to influenza B. Fewer 4-fold rises were seen in those with preexisting antibody. The results of microneutralization assays to H3N2 correlated well with HAI results. The time for antibody to decay to one-half of the postvaccination titer (t1/2) was approximately 126 days for H1N1 and 258 days for H3N2. CONCLUSIONS: Although not all children responded with 4-fold rises in antibody or achieved the putative protective titer of > or =1:32, the half-life of antibody suggested that children immunized in the fall should have immune responses sustained throughout the ensuing influenza season.     

Interferon production in children with respiratory syncytial, influenza, and parainfluenza virus infections.

To better understand the recovery process of infants with lower respiratory tract disease due to respiratory syncytial virus, the production of interferon by 129 children (ages 10 days to 24 months) with RSV infection was compared to that of 20 children with influenza (ages 1 to 36 months), and 37 children with parainfluenza virus infection (ages 4 to 66 months). Interferon assays of 285 nasal washes from children with RSV revealed that interferon production occurred in only 5 (4%) of the children. Significantly more children infected with infleunza virus, 55% (P less than 0.001), and parainfluenza virus, 30% (P less than 0.001), produced interferon. In addition, the quantity of interferon produced by children with RSV (geometric mean titer = 2) was significantly less than that of children with influenza (GMT = 26.8, P less than 0.001) and parainfluenza virus (GMT = 23.5, P less than 0.001). In the children infected with RSV, in constrast to those with influenza, interferon detection was not associated with diminished shedding of virus.     

Humoral and cellular immune responses in children given annual immunization with trivalent inactivated influenza vaccine

BACKGROUND: There have been no prior reports of the frequency of circulating influenza-specific, interferon gamma-producing memory CD4+ and CD8+ T-cells in healthy children who have received multiple influenza immunizations. METHODS: We evaluated 21 previously immunized children, ages 3 to 9 years, before and 1 month after administration of trivalent inactivated influenza vaccine. Frequencies of influenza-specific CD4+ and CD8+ T-cells stimulated with trivalent inactivated influenza vaccine or A/Panama (H3N2) virus were determined by flow cytometry, and antibody responses to vaccine strains and a drifted H3N2 strain were measured by hemagglutination inhibition assay and neutralizing antibody assays. RESULTS: Mean change in CD4+ and in CD8+ T-cell frequencies after immunization was 0.01% (P > 0.39) with postimmunization CD4+ frequencies higher than CD8+ frequencies. Children with more previous vaccinations had a higher baseline frequency of CD4+ T-cells (P = 0.0002) but a smaller increase or even a decline from baseline after immunization (P = 0.003). An association between age and change in frequency was not detected. Baseline geometric mean titers (GMTs) and seroprotection rates were significantly higher in older children against A/Panama (neutralizing baseline GMT, P = 0.0488) and A/New Caledonia (hemagglutination inhibition baseline GMT and seroprotection, P < 0.0297). Baseline GMTs against B/Hong Kong were not associated with age or quantity of prior vaccinations. CONCLUSIONS: These findings suggest that children may plateau in CD4+ T-cell responses to influenza antigens with repeated exposures and that the number of exposures may play a large role in building a memory CD4+ T-cell response to influenza A, perhaps independently from age.     

Clinical reactions and serologic response following inactivated monovalent influenza type B vaccine in young children and infants.

A monovalent, zonally purified, inactivated influenza B vaccine was administered to 29 children, 3 to 6 years of age, and 16 infants, 12 to 28 months of age, as a single dose of 0.25 ml containing 250 chick cell agglutinating units. The vaccine was both antigenic and well tolerated in the older group of preschool children. In the infants the vaccine was also antigenic but poorly tolerated clinically. Febrile reactions to 102 or greater were seen in 9 of the 16 infants, and two of these infants experienced a seizure following vaccination. The clinical reactions observed with the administration of influenza B vaccine in the dose used in this study would suggest significant limitations on its use in children under 3 years of age.