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There is limited understanding of antibody responses in children across different SARS-CoV-2 variants. As part of an ongoing household cohort study, we assessed the antibody response among unvaccinated children infected with Wuhan, Delta, or Omicron variants, as well as vaccinated children with breakthrough Omicron infection, using a SARS-CoV-2 S1-specific IgG assay and surrogate virus neutralization test (% inhibition). Most children infected with Delta (100%, 35/35) or Omicron (81.3%, 13/16) variants seroconverted by one month following infection. In contrast, 37.5% (21/56) children infected with Wuhan seroconverted, as previously reported. However, Omicron-infected children (geometric mean concentration 46.4 binding antibody units/ml; % inhibition = 16.3%) mounted a significantly lower antibody response than Delta (435.5 binding antibody untis/mL, % inhibition = 76.9%) or Wuhan (359.0 binding antibody units/mL, % inhibition = 74.0%). Vaccinated children with breakthrough Omicron infection mounted the highest antibody response (2856 binding antibody units/mL, % inhibition = 96.5%). Our findings suggest that despite a high seropositivity rate, Omicron infection in children results in lower antibody levels and function compared with Wuhan or Delta infection or with vaccinated children with breakthrough Omicron infection. Our data have important implications for public health measures and vaccination strategies to protect children. Despite a rise in COVID-19 cases among children, there is limited understanding of the antibody responses mounted, compared to in adults. In this work, authors compare seroconversion rates and antibody responses in unvaccinated Australian children across the three SARS-CoV-2 waves (Wuhan, Delta and Omicron). [ABSTRACT FROM AUTHOR]

Children have mild severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) confirmed disease (COVID-19) compared to adults and the immunological mechanisms underlying this difference remain unclear. Here, we report acute and convalescent innate immune responses in 48 children and 70 adults infected with, or exposed to, SARS-CoV-2. We find clinically mild SARS-CoV-2 infection in children is characterised by reduced circulating subsets of monocytes (classical, intermediate, non-classical), dendritic cells and natural killer cells during the acute phase. In contrast, SARS-CoV-2-infected adults show reduced proportions of non-classical monocytes only. We also observe increased proportions of CD63+ activated neutrophils during the acute phase to SARS-CoV-2 in infected children. Children and adults exposed to SARS-CoV-2 but negative on PCR testing display increased proportions of low-density neutrophils that we observe up to 7 weeks post exposure. This study characterises the innate immune response during SARS-CoV-2 infection and household exposure in children. Childhood infection with SARS CoV2 is associated with a milder course of infection but the immunopathogenesis of this remains unclear. Here the authors explore immunological differences in the innate immune system during acute and convalescent SARS CoV2 infection in the young. [ABSTRACT FROM AUTHOR]

Introduction: Australia is traditionally an early adopter of vaccines, therefore comprehensive and effective post-licensure vaccine pharmacovigilance is critical to maintain confidence in immunisation, both nationally and internationally. With adverse event following immunisation (AEFI) surveillance the responsibility of Australian jurisdictions, Victoria operates an enhanced passive AEFI surveillance system integrated with clinical services, called 'SAEFVIC' (Surveillance of Adverse Events Following Vaccination In the Community).Objective: The aim of this study was to evaluate Victoria's current AEFI surveillance system 'SAEFVIC' and inform ongoing quality improvement of vaccine pharmacovigilance in Victoria and Australia.Methods: We conducted a retrospective structured desktop evaluation of AEFI reporting received by SAEFVIC from 2007 to 2014, to evaluate the system according to its stated objectives, i.e. to improve AEFI reporting; provide AEFI signal detection; and to maintain consumer confidence in vaccination.Results: AEFI reporting has tripled since SAEFVIC commenced (incidence risk ratio [IRR] 3.04, 95% confidence interval [CI] 2.35-3.93), raising Victoria to be the lead jurisdiction by AEFI reporting volume and to rank third by population reporting rate nationally. The largest increase was observed in children. Data were utilised to investigate potential signal events and inform vaccine policy. Signal detection required clinical suspicion by surveillance nurses, or prior vaccine-specific concerns. Subsequent vaccination post-AEFI was documented for 56.2% (95% CI 54.1-58.4) of reports, and the proportion of children due or overdue for vaccination was 2.3% higher for those reporting AEFI compared with the general population.Conclusion: SAEFVIC has improved AEFI surveillance, facilitates signal investigation and validation, and supports consumer confidence in immunisation. Expansion of the system nationally has the potential to improve capacity and capability of vaccine pharmacovigilance, particularly through data consistency and jurisdictional comparability in Australia. [ABSTRACT FROM AUTHOR]

Background: Bacillus Calmette-Guérin (BCG) vaccine is used worldwide, with high efficacy against childhood Mycobacterium tuberculosis (TB) meningitis and miliary TB. BCG vaccine is considered safe, with serious systematic adverse events following immunization (AEFI) of immunocompetent recipients being rare, although adverse event rates vary between differing BCG strains. In Victoria, Australia, AEFI are reported to SAEFVIC (Surveillance of Adverse Events Following Vaccination In the Community), an enhanced passive surveillance system operational since 2007.Objective: To describe the epidemiology of reported BCG AEFI in Victoria, Australia, particularly following the 2012 recall of Connaught BCG vaccine, substitution with Denmark-SSI vaccine and subsequent programme delivery adjustments.Methods: Retrospective analysis of reported BCG AEFI in Victoria, Australia, for the 6-year period 2008-2013. Incidence rates were calculated using available doses-distributed, doses-administered and population data denominators with 95 % confidence intervals.Results: The predominant BCG AEFI reported were abscess and lymphadenopathy, with higher reports for males than for females (p = 0.039).The rates of AEFI per 10,000 doses distributed were similar for the Connaught and Denmark-SSI strains, at 11.6 and 15.4, respectively (p = 0.414). When doses administered rather than doses distributed were considered, the rate of reported Denmark-SSI AEFI was much higher, at 62.8 per 10,000 doses administered. Meaningful result interpretation was hampered by a lack of a BCG vaccination register, multiple disparate providers and absent doses-administered data prior to the recall.Conclusion: Effective AEFI surveillance is of paramount importance as countries are faced with unplanned vaccine strain changes following the 2012 BCG recall and subsequent global vaccine supply shortages. The Australian experience and lessons learned serve as a timely reminder to BCG vaccination programmes worldwide to review AEFI surveillance systems. [ABSTRACT FROM AUTHOR]