COVID-19 vaccine strategies for Aotearoa New Zealand: a mathematical modelling study.

Abstract

<b>Background:</b> COVID-19 elimination measures, including border closures have been applied in New Zealand. We have modelled the potential effect of vaccination programmes for opening borders. <b>Methods:</b> We used a deterministic age-stratified Susceptible, Exposed, Infectious, Recovered (SEIR) model. We minimised spread by varying the age-stratified vaccine allocation to find the minimum herd immunity requirements (the effective reproduction number R_eff<1 with closed borders) under various vaccine effectiveness (VE) scenarios and R₀ values. We ran two-year open-border simulations for two vaccine strategies: minimising R_eff and targeting high-risk groups. <b>Findings:</b> Targeting of high-risk groups will result in lower hospitalisations and deaths in most scenarios. Reaching the herd immunity threshold (HIT) with a vaccine of 90% VE against disease and 80% VE against infection requires at least 86•5% total population uptake for R₀=4•5 (with high vaccination coverage for 30-49-year-olds) and 98•1% uptake for R₀=6. In a two-year open-border scenario with 10 overseas cases daily and 90% total population vaccine uptake (including 0-15 year olds) with the same vaccine, the strategy of targeting high-risk groups is close to achieving HIT, with an estimated 11,400 total hospitalisations (peak 324 active and 36 new daily cases in hospitals), and 1,030 total deaths. <b>Interpretation:</b> Targeting high-risk groups for vaccination will result in fewer hospitalisations and deaths with open borders compared to targeting reduced transmission. With a highly effective vaccine and a high total uptake, opening borders will result in increasing cases, hospitalisations, and deaths. Other public health and social measures will still be required as part of an effective pandemic response. <b>Funding:</b> This project was funded by the Health Research Council [20/1018]. <b>Research in context</b>.