(CNN)The 2020 Summer Olympics are finally underway in Tokyo.
Competition began Wednesday, more than a year after the original start date after the Games were delayed due to the pandemic.
But with Covid-19 still spreading unchecked in Japan, organizers have been forced to take unprecedented steps to keep competitors and the public safe.
Athletes who contracted coronavirus have seen their Olympic dreams dashed. Some tested positive in Japan, some before coming.
These are the athletes we know who have publicly dropped out due to Covid-19 health and safety protocols.
Team USA: 5
Katie Lou Samuelson -- Women's 3x3 basketball
Team Czech Republic: 6
Simon Nausch -- Coach, women's beach volleyball
Ondrej Perusic -- Men's beach volleyball
Michal Schlegel -- Men's cycling
Pavel Širuček -- Men's table tennis
Team Great Britain: 3
Dan Evans -- Men's tennis
Amber Hill -- Women's shooting
Johanna Konta -- Women's tennis
Team Mexico: 2
Hector Velazquez -- Baseball
Sammy Solis -- Baseball
Team Netherlands: 2
Finn Florijn -- Men's rowing
Candy Jacobs -- Women's skateboarding
Team South Africa: 2
Kamohelo Mahlatsi -- Men's football
Thabiso Monyane -- Men's football
Team Australia: 1
Alex de Minaur -- Men's tennis
Team Chile: 1
Fernanda Aguirre -- Women's taekwondo
Team Portugal: 1
Frederico Morais -- Men's surfing
Team ROC (Russian Olympic Committee): 1
Ilya Borodin -- Men's Swimming