Organisers confirmed the move as part of updated COVID-19 guidelines published for the annual event.

Around 35,000 people have registered for the 2021 Chicago Marathon, which was cancelled last year due to the COVID-19 pandemic.

"Registered participants are required to provide proof of a complete COVID-19 vaccination series or a negative COVID-19 test result to participate in the 2021 Bank of America Chicago Marathon," organisers said.

"Registered participants who are not fully vaccinated are required to provide a negative COVID-19 test result for a test administered within 72 hours of attending the Bank of America Chicago Marathon.

"The event defines 'fully vaccinated' as individuals who are two weeks after their second dose in a two-dose vaccine series or two weeks after a single-dose vaccine.

"Proof of vaccination (hard copy, photocopy or digital version of an immunization record) or a negative COVID-19 test taken within 72 hours of attending the event is required for entrance to the Abbott Health & Fitness Expo.

"Individuals unable to prove full vaccination or negative test will be barred from entering the Health and Fitness Expo and unable to pick up the necessary race materials that allow for participation in the event."

Organisers say RT-PCR, RT-LAMP, lateral flow, and rapid antigen tests are approved.

Attendees will be required to wear face coverings while at indoor event venues, while participants are encouraged to wear face coverings in Grant Park prior to starting the race.

Ethiopia’s Getaneh Molla and Seifu Tura, Kenya’s Ruth Chepngetich, and Americans Keira D’Amato and Emma Bates have become the latest elite athletes to join the start list for this year’s event.

Two-times Olympic medallist Galen Rupp and Sara Hall were announced earlier this year, with the pair expected to lead the United States’ challenge in the men’s and women’s events, respectively.

Molla has the fastest personal best in the men’s field as he clocked 2 hours 3min 34sec to win the 2019 Dubai Marathon.

Chepngetich is the reigning women’s world champion, with the Kenyan poised to make her Chicago Marathon debut.

She set the world record in the half marathon this spring in 1:04:02, while her marathon personal best of 2:17:08 makes her the fourth fastest woman in history.

Daniel Romanchuk and Tatyana McFadden are among the US stars set to feature in the elite wheelchair races, with Switzerland’s Marcel Hug also included on the start list.