Lack of guaranteed medics and marshals meant event had to be cancelled
Other dates were considered for this year's Southern 100, but the event couldn't guarantee medical cover and marshals would be available.
The Billown meeting was called off earlier this week after it was announced border restrictions are expected to remain in place to some extent until September.
The Classic TT and Manx Grand Prix have also confirmed they won't be going ahead, with the 2021 TT having been called off in December.
Phil Edge from the Southern 100 says rescheduling wasn't possible:
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