are when we infect each other with covid. >> reporter: pro sports teams demonstrating how the virus is spreading, odell beckham jr. scored monday night, next morning joined the long list of players and staff testing positive or quarantining after exposure. >> they're really a window into community spread, and kudos to the sports leagues because they are actually doing a fantastic job of surveillance testing and the rest of the country, we're driving a car down a dark road with the headlights off while looking in the rearview mirror. >> reporter: this afternoon. >> they have 15 yeses, zero noes. >> reporter: cdc vaccine advisers unanimous in recommending the cdc change its guidance to say that the pfizer and moderna vaccines are preferred over the j&j. why? well, those very rare blood clots connected to the j&j that can be fatal. nick watt, cnn, los angeles. >> thank you very much for that. joining me now is an