Vaccine effectiveness against medically attended, laboratory-confirmed influenza among children aged 6 to 59 months, 2003-2004
ABSTRACT Influenza is a leading cause of illness among children. Studies rarely have measured influenza vaccine effectiveness among young children, particularly when antigenic match between vaccine and circulating viruses is suboptimal. We assessed vaccine effectiveness against medically attended, laboratory-confirmed influenza for children who were aged 6 to 59 months during the 2003-2004 influenza season.
In a case-control study that was conducted in a single pediatric practice, case patients who were aged 6 to 59 months and had laboratory-confirmed influenza were age matched 1:2 to eligible control subjects. Vaccination status was ascertained as of the date of the case patient's symptom onset. Conditional logistic regression was used to calculate vaccine effectiveness, adjusting for underlying medical conditions and health care usage.
We identified 290 influenza case patients who were seen for medical care from November 1, 2003, to January 31, 2004. Vaccine effectiveness among fully vaccinated children, compared with unvaccinated children, was 49%. Partially vaccinated children who were aged 6 to 23 months had no significant reduction in influenza (vaccine effectiveness: -70%), but partially vaccinated children who were aged 24 to 59 months had a significant (65%) reduction in influenza, compared with unvaccinated children.
Full vaccination provided measurable protection against laboratory-confirmed influenza among children who were aged 6 to 59 months during a season with suboptimal vaccine match. No vaccine effectiveness was identified with partial vaccination among children who were aged 6 to 23 months, affirming that children need to be fully vaccinated to obtain protective effects. These results strengthen the evidence of the vaccine's ability to reduce substantially the burden of disease in this age group.
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ABSTRACT: Few studies report the effectiveness of trivalent inactivated influenza vaccine (TIV) in preventing hospitalisation for influenza-confirmed respiratory infections. Using a prospective surveillance platform, this study reports the first such estimate from a well-defined ethnically diverse population in New Zealand (NZ). A case test-negative design was used to estimate propensity adjusted vaccine effectiveness. Patients with a severe acute respiratory infection (SARI), defined as a patient of any age requiring hospitalisation with a history of a fever or a measured temperature ≥38°C and cough and onset within the past 7 days, admitted to public hospitals in South and Central Auckland were eligible for inclusion in the study. Cases were SARI patients who tested positive for influenza, while non-cases (controls) were SARI patients who tested negative. Results were adjusted for the propensity to be vaccinated and the timing of the influenza season. The propensity and season adjusted vaccine effectiveness (VE) was estimated as 39% (95% CI 16;56). The VE point estimate against influenza A (H1N1) was lower than for influenza B or influenza A (H3N2) but confidence intervals were wide and overlapping. Estimated VE was 59% (95% CI 26;77) in patients aged 45-64 years but only 8% (-78;53) in those aged 65 years and above. Prospective surveillance for SARI has been successfully established in NZ. This study for the first year, the 2012 influenza season, has shown low to moderate protection by TIV against influenza positive hospitalisation.Vaccine 04/2014; DOI:10.1016/j.vaccine.2014.04.013 · 3.49 Impact Factor
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ABSTRACT: In this study, we assessed the effects of the pre-vaccination titer and age on the immunogenicity of a low dose of influenza vaccine in children less than 4 years of age. A total of 259 children received two vaccine doses (0.1 ml for 0-year-olds and 0.2 ml for children 1 year of age or older) four weeks apart during the 2005/2006 season. The hemaggulutination inhibition antibody titers were measured before vaccination and four weeks after the first and second dose. The geometric mean titer, mean fold rise, seroresponse proportion (≥4-fold rise in titer) and seroprotection proportion (titer≥1:40) were calculated for the pre-vaccination titer and age categories. A multivariate logistic regression analysis was performed using the seroresponse and seroprotection proportions as dependent variables and the pre-vaccination titer and age as explanatory variables. As for the seroresponse against H1 antigen after the first dose, the adjusted odds ratio of the pre-vaccination titers (vs. <1:10) was 2.2 (95% confidence interval: 0.8-5.8) at 1:10 to 1:20 and 0.14 (0.04-0.49) at ≥1:40. The corresponding figures for ages were 0.03 (0.01-0.07) for the 0-year-olds and 0.17 (0.08-0.34) for the 1-year-olds compared with the 2- to 3-year-olds (trend P<0.001). Similar results were also obtained for the H3 and B strains. Significantly elevated odds ratios for seroprotection were observed, with greater pre-vaccination titers and older ages, for all strains. The pre-vaccination titer and age were independently associated with the antibody response in young children. The immune response was weaker in the younger children and those without preexisting immunity.Clinical and vaccine Immunology: CVI 07/2014; 21(9). DOI:10.1128/CVI.00200-14 · 2.37 Impact Factor
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ABSTRACT: Background: As the influenza A H1N1 pandemic emerged in 2009, children were found to experience high morbidity and mortality and were prioritized for vaccination. This multicenter, randomized, double-blind, age-stratified trial assessed the safety and immunogenicity of inactivated influenza A(H1N1)pdm09 vaccine in healthy children aged 6 months to 17 years. Methods: Children received 2 doses of approximately 15 or 30 g hemagglutin antigen 21 days apart. Reactogenicity was assessed for 8 days after each dose, adverse events through day 42, and serious adverse events or new-onset chronic illnesses through day 201. Serum hemagglutination inhibition titers were measured on days 0 (prevaccination), 8, 21, 29 and 42. Results: A total of 583 children received the first dose and 571 received the second dose of vaccine. Vaccinations were generally well-tolerated and no related serious adverse events were observed. The 15 g dosage elicited a seroprotective hemagglutination inhibition (>= 1: 40) in 20%, 47% and 93% of children in the 6-35 month, 3-9 year and 10-17 year age strata 21 days after dose 1 and in 78%, 82% and 98% of children 21 days after dose 2, respectively. The 30 g vaccine dosage induced similar responses. Conclusions: The inactivated influenza A(H1N1) pdm09 vaccine exhibited a favorable safety profile at both dosage levels. While a single 15 or 30 g dose induced seroprotective antibody responses in most children 10-17 years of age, younger children required 2 doses, even when receiving dosages 4- to 6-fold higher than recommended. Well-tolerated vaccines are needed that induce immunity after a single dose for use in young children during influenza pandemics.The Pediatric Infectious Disease Journal 08/2014; 33(8):865-871. DOI:10.1097/INF.0000000000000329 · 3.14 Impact Factor