Some may be discouraged by this as the event isn't for another three months and the disease isn't that dangerous for healthy people and that the vaccine is already being rolled out.
That being said, they only have 800,000 doses on hand right now. That sounds like a lot but there is something like 5 million people living in Britain over the age of 70 and you divie 800,000 by two if you want 90% immunity. Still in 3 months, I imagine you could have a VERY high percentage of the senior citizens vaccinated. 80% of all covid deaths in the US are people over the age of 65 and I imagine that figure is similar in the UK.
https://athleticsweekly.com/athletics-news/english-national-is-postponed-1039938282/
https://www.aarp.org/health/conditions-treatments/info-2020/coronavirus-deaths-older-adults.html