Short and medium-term challenges for COVID-19 vaccination: from prioritisation to the relaxation of measures
2021
Background
The roll-out of COVID-19 vaccines is a multi-faceted challenge whose performance depends
on pace of vaccination, vaccine characteristics and heterogeneities in individual risks.
Methods
We developed a mathematical model accounting for the risk of severe disease by age and
comorbidity and transmission dynamics. We compared vaccine prioritisation strategies in the
early roll-out stage and quantified the extent to which measures could be relaxed as a function
of the vaccine coverage achieved in France.
Findings
Prioritizing at-risk individuals reduces morbi-mortality the most if vaccines only reduce
severity, but is of less importance if vaccines also substantially reduce infectivity or
susceptibility. Age is the most important factor to consider for prioritization; additionally
accounting for comorbidities increases the performance of the campaign in a context of scarce
resources. Vaccinating 90% of ≥65 y.o. and 70% of 18-64 y.o. before the autumn 2021 with a
vaccine that reduces severity by 90% and susceptibility by 80%, we find that control measures
reducing transmission rates by 15-27% should be maintained to remain below 1,000 daily
hospital admissions in France with a highly transmissible variant (basic reproduction number
R0=4). Assuming 90% of ≥65 y.o. are vaccinated, full relaxation of control measures might be
achieved with a vaccine coverage of 89-100% in 18-64 y.o or 60-69% of 0-64 y.o.
Interpretation
Even in optimistic scenarios, current vaccination intentions in the French populations might
not allow a complete relaxation of control measures. Vaccination of children, if possible, could
help achieve this objective.
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