When a large proportion of the world’s population is still awaiting access to primary immunisation, communication about vaccines should emphasise efficacy against severe outcomes and death rather than against breakthrough infections, to not weaken public trust in them, even more so when non-pharmaceutical interventions (eg, mask wearing and physical distancing) are being lifted. International and national public health authorities should provide evidence-based, transparent, and balanced decisions about vaccine updates, dosing, and timing, based on accurate monitoring and shared values.
We also believe that public health should prioritise new pathways of research. Next to a rigorous safety surveillance system, an international, multicentric efficacy-studying programme should be put in place to provide updated immunosurveillance data. Because evidence on vaccine effectiveness can have multiple sources of bias, results need to be stratified by vaccine type and schedule, demographic group, health status, level of immune response, and—last but not least—viral variants. Given that the potential to collect timely experimental data is limited, real-world vaccine evaluation relies on observational studies
measuring infection, hospitalisation, and mortality outcomes. Both longitudinal cohorts of vaccinated and unvaccinated individuals and case-control studies, comparing the vaccination status of infected cases and controls, should be further promoted. Among case-control studies, the test-negative design, bypassing some of the most common biases (eg, health-care-seeking behaviours and population differences), has been already effective in studying influenza vaccines, and it is being used to accumulate evidence on COVID-19. In these respects, digital health tools, linking electronic immunisation records with other national databases (eg, infections and comorbidities records) and exploiting innovative data collection instruments, as Menni and colleagues reported, could provide a game-changer approach to quickly estimating population-level vaccination effectiveness. Yet, combining large volumes of data to perform comprehensive analyses requires an enhancement of digital tools’ interoperability, structured databases, and connected infrastructures.