London Marathon organisers are “very optimistic” a record 50,000 runners will be able to take part in the race when it is held on 3 October.
The 2020 race involved only elite athletes running a specially designed closed-loop course because of the coronavirus pandemic.
Event director Hugh Brasher said he hoped the vaccination programme would allow amateur runners to participate.
The government is aiming to offer every adult in the UK a vaccine by autumn.
Reaching the 50,000 target would involve marathon organisers accommodating a record number of people on the course.
A record 42,906 started the 2019 race. Organisers estimate the event also attracts about 750,000 spectators and needs about 6,000 volunteers to help on the day.
Event director Hugh Brasher told BBC Sport: “The government has been talking about the fact that everyone will be vaccinated in the country by September. This is 3 October, so we really hope that this is a beacon of hope in the future. And that we really are living in a different world to what we are now in.
“We’re talking to scientists, we’re talking to other organisers around the world, where events are happening around the world, how they have happened. And that’s why we are positive about 3 October.”
For the second year in a row, the race has been moved from its traditional April date.
In addition to the runners taking part in London, organisers are also inviting another 50,000 people to complete the 26.2 miles virtually using a tracking app.
Last year 38,000 runners took part virtually.
“The London Marathon has to do what is right for society,” added Brasher. “It is far bigger than just for the runners. This is about the National Health Service, this is about charities, this is about communities. It is about bringing people together.
“We are incredibly positive that we will be able to have 50,000 people running the London Marathon in person in 2021. Time will tell.”
Prospective runners who have entered the ballot for a place in the 2021 race will find out if they have been successful on 8 February.
Unsuccessful applicants will then have a week to enter the virtual event before it is opened up to the rest of the public.
The ballot to run in the 2020 race attracted a record 457,861 entries.
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