The decision was announced in the wake of a Swiss Federal court decision to maintain the ban on events that saw 1000 or more people in the same location.
The world championships were the first event confirmed in the new cycling season, and the UCI's feature event had come under fire for clashing with the end of the Tour de France, which would see a number of top time triallists unable to participate in the event.
The UCI confirmed the decision via a press release, full version here.
"The Union Cycliste Internationale (UCI) takes note of the Swiss Federal Council’s decision – linked to the current Covid-19 pandemic – to maintain, until 30 September 2020, the ban on events uniting more than 1000 people.
"Given this decision, the organising committee of the Aigle-Martigny 2020 UCI Road World Championships and the political authorities of the cantons concerned have sadly estimated that the conditions could no longer be met to host the event scheduled to take pace in Aigle (Vaud) and Martigny (Valais).
The UCI therefore acknowledges that the 2020 UCI Road World Championships will not take place in Aigle-Martigny."
UCI president David Lappartient last month said that there was "no plan B" for the World Championships should Switzerland be unable to host the races. Despite that, the UCI is unwilling to give up on the staging of the world championships in an alternative location for 2020, with September 1 set as the deadline for the decision.
"Given the sporting importance of the UCI Road World Championships for cycling, the UCI would like to clarify that it will work towards finding an alternative project to ensure the 2020 edition of the event can take place, with the priority being in Europe and at the dates initially scheduled.
"It could include all or some of the planned races. The UCI will look for a host city that would be able to provide a route as challenging as that in Aigle-Martigny and which would therefore suit the same type of riders who had initially planned to participate in Switzerland."
Cycling Australia (CA) has recently confirmed that they will not be sending teams to overseas events, though they had flagged the road world championships as an event where an exception could be made. The CA announcement also stated that only elite riders would be considered for the event, with Under-23s and juniors not in consideration for 2020 selection.