Are planes safe during COVID?

Well, but its said that the covid virus can reproduce at an incredible rate once it's in the body and it initially usually goes undetected by the body's defenses as it's deign allows it to be accepted by the ace receptors. So doesn't that mean even one virus particle is enough to infect a person? And if one particle is enough, then why do people say the infectious level is anywhere between a 100 and 1000?