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The unprecedented speed of delivery of SARS-CoV-2 pandemic vaccines has redefined the limits for all vaccine development. Beyond the aspirational 100-day timeline for tomorrow's hypothetical pandemic vaccines, there is a sense of optimism that development of other high priority vaccines can be accelerated. Early in the COVID-19 pandemic, an intense and polarised academic and public discourse arose concerning the role of human challenge trials for vaccine development. A case was made for human challenge trials as a powerful tool to establish early proof-of-concept of vaccine efficacy in humans, inform vaccine down selection, and address crucial knowledge gaps regarding transmission, pathogenesis, and immune protection. We review the track record of human challenge trials contributing to the development of vaccines for 19 different pathogens and discuss relevant limitations, barriers, and pitfalls. This Review also highlights opportunities for efforts to broaden the scope and boost the effects of human challenge trials, to accelerate all vaccine development., Competing Interests: Declaration of interests Y-NA is supported by a National Health and Medical Research Council (NHMRC) and Heart Foundation PhD scholarship. EJ is supported by the Wellcome Trust and the Moh Family Foundation. JO is supported by an NHMRC Investigator grant and Melbourne Children's Campus Clinician–Scientist fellowship. ACS is supported by an NHMRC Investigator grant and Viertel Senior Medical Research fellowship. JSM is supported by an NHMRC Investigator grant. All authors are Human Infection Challenge Network for Vaccine Development members. The authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Aim: To describe the epidemiology of respiratory viruses in children before and during the 2020 SARS-CoV-2 pandemic and the relationship to public health measures instituted by the Victorian government., Methods: Retrospective audit of respiratory viruses at a tertiary paediatric hospital in Melbourne from January 2015 up to week 47, 2020 in children under 18 years of age. The proportion of positive cases in weeks 1-47 in 2015-2019 (period 1) were compared to weeks 1-47, 2020 (period 2), and reviewed in the context of public health restrictions in Victoria., Results: An annual average of 4636 tests were performed in period 1 compared to 3659 tests in period 2. Proportions of positive influenza A virus, influenza B virus, respiratory syncytial virus (RSV) and human parainfluenza virus were significantly reduced in period 2 compared to period 1: 77.3, 89.4, 68.6 and 66.9% reductions, respectively (all P < 0.001). From week 12-47, 2020, 28 893 SARS-CoV-2 tests were performed with a 0.64% positivity rate. Influenza viruses were not detected after week 17, RSV was not detected after week 35., Conclusions: Strict public health measures and border closures were successful in eliminating community transmission of SARS-CoV-2 in Melbourne. This was associated with a significant reduction in other respiratory virus infections in children. Identifying sustainable and effective ongoing public health interventions to reduce transmission of RSV and influenza could result in reduced morbidity and mortality in children and requires further research., (© 2021 Paediatrics and Child Health Division (The Royal Australasian College of Physicians).)