The Tour de France stepped up protective measures on Sunday, to "limit health risks" in the face of a resurgence of Covid-19, which has affected several riders in recent days.
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Masks must now be worn by everyone, including organisers, guests and journalists, who may be "in contact with the riders and members of the cycling teams" before and after the stages, said organisers Amaury Sport Organisation (ASO).
Several riders, including Britain's Tom Pidcock and Spain's Juan Ayuso, a teammate of yellow jersey Tadej Pogacar, have already retired after testing positive.
Pogacar said before the start of the race that he had been affected by the virus in mid-June while 2018 winner Geraint Thomas is continuing the Tour for the time being despite "slight symptoms".
Several riders such as Remco Evenepoel, who is third overall, have already started wearing masks again over the last few days with the Belgian explaining he was doing so because the journalists in front of him were not wearing them.