Build more capacity, and stretch what we already have

Wiecek: WAW Statistical Consulting. Athey acknowledges a generous gift from Schmidt Futures. Ahuja and Kremer acknowledge generous funding from the Wellspring Philanthropic Fund. Baker and Wiecek acknowledge generous funding from Emergent Ventures. Kominers acknowledges generous funding from the Washington Center for Equitable Growth. For contributing input and expertise, we are indebted to numerous experts in vaccine procurement from international organizations and governments. Whit

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Due to the enormous economic, health, and social costs of the COVID-19 pandemic, there are high expected social returns to investing in parallel in multiple approaches to accelerating vaccination. We argue there are high expected social returns to investigating the scope for lowering the dosage of some COVID-19 vaccines. While existing evidence is not dispositive, available clinical data on the immunogenicity of lower doses combined with evidence of a high correlation between neutralizing antibody response and vaccine efficacy suggests that half or even quarter doses of some vaccines could generate high levels of protection, particularly against severe disease and death, while potentially expanding supply by 450 million to 1.55 billion doses per month, based on supply projections for 2021. An epidemiological model suggests that, even if fractional doses are less effective than standard doses, vaccinating more people faster could substantially reduce total infections and deaths. The costs of further testing alternative doses are much lower than the expected public health and economic benefits. However, commercial incentives to generate evidence on fractional dosing are weak, suggesting that testing may not occur without public investment. Governments could support either experimental or observational evaluations of fractional dosing, for either primary or booster shots. Discussions with researchers and government officials in multiple countries where vaccines are scarce suggests strong interest in these approaches.

Background Few studies have assessed participant safety in human challenge trials (HCTs). Key questions regarding HCTs include how risky such trials have been, how often adverse events (AEs) and serious adverse events (SAEs) occur, and whether risk mitigation measures have been effective. Methods A systematic search of PubMed and PubMed Central for articles reporting on results of HCTs published between 1980 and 2021 was performed and completed by 10/7/2021. Results Of 2,838 articles screened, 276 were reviewed in full. 15,046 challenged participants were described in 308 studies that met inclusion criteria. 286 (92.9%) of these studies reported mitigation measures used to minimize risk to the challenge population. Among 187 studies which reported on SAEs, 0.2% of participants experienced at least one challenge-related SAE. Among 94 studies that graded AEs by severity, challenge-related AEs graded “severe” were reported by between 5.6% and 15.8% of participants. AE data were provided as a range to account for unclear reporting. 80% of studies published after 2010 were registered in a trials database. Conclusions HCTs are increasingly common and used for an expanding list of diseases. Although AEs occur, severe AEs and SAEs are rare. Reporting has improved over time, though not all papers provide a comprehensive report of relevant health impacts. We found very few severe symptoms or SAEs in studies that reported them, but many HCTs did not report relevant safety data. This study was pre-registered on PROSPERO as CRD42021247218.