The Impact of SARS-CoV-2 Vaccine Dose Separation and Dose Targeting on Hospital Admissions and Deaths from COVID-19 in England

Abstract

In late 2020, the JCVI (the Joint Committee on Vaccination and Immunisation, which provides advice to the Department of Health and Social Care, England) made two important recommendations for the initial roll-out of the COVID-19 vaccine. The first was that vaccines should be targeted to the elderly and vulnerable, with the aim of maximally preventing disease rather than infection - a prioritisation that has become the adopted practice in many countries. The second was to increase the interval between first and second doses for 3 to 12-weeks, which both accounted for the observation that the ChAdOx vaccine appeared to have a higher efficacy with this longer dose interval, and that by delaying second doses the capacity to deliver first doses was increased. Here, using the latest data on vaccine efficacy we re-examine these recommendations through a mathe- matical model, to understand their short and medium-term impacts in England. In particular, we show that targeting the most vulnerable had the biggest immediate impact (compared to targeting younger individuals who may be more responsible for transmission). The 12-week delay was also highly beneficial, estimated to have averted between 32-72 thousand hospital admissions and 4-9 thousand deaths over the first ten months of the campaign (December 2020 - September 2021) - depending on the assumed interaction between dose interval and efficacy.