A new study by researchers at Imperial College London has estimated that the UK policy of delaying the interval between first and second COVID-19 vaccines prevented 64,000 hospital admissions and 9,400 deaths between 8th December 2020 and 13th September 2021.
The UK was the first country to begin rolling out the COVID-19 vaccines, initially administering doses three weeks apart. However, early evidence of high vaccine effectiveness after the first dose, together with the emergence of the Alpha variant, prompted the UK to extend the interval between doses to 12 weeks in order to quickly achieve as many first doses as possible.
This new study, published as a preprint (and therefore not yet peer reviewed), set out to quantify the impact of this decision to extend the interval between vaccine doses.
The researchers used a previously established model of transmission of the virus alongside English surveillance data on hospital admissions, hospital occupancy, immunity in the population and rates of infection.
They modelled the trajectory the epidemic would have taken if vaccine doses had continued to be administered three weeks apart, and compared this with the real vaccine roll-out schedule. They then estimated and compared the resulting number of daily infections, hospital admissions and deaths. Different scenarios spanning a range of assumptions about vaccine effectiveness and waning were investigated.
They estimated that increasing the interval between the first and second vaccine doses from three to 12 weeks prevented around 64,000 hospital admissions and 9,400 deaths between 8th December 2020 and 13th September 2021. Similarly, they estimated that continuing with the three-week interval would have resulted in more infections and deaths, compared to the longer interval. Their model also showed that the three-week interval would have resulted in a greater number of hospital admissions.
The researchers concluded that the strategy of rapidly providing one dose of vaccine to a larger proportion of the population was successful in reducing COVID-19 hospitalisations and deaths.
They also suggested that guidelines on vaccine strategy would continue to need careful consideration and adaptation in light of new emerging evidence about vaccine protection within the population.