(CNN)In one week, there were nine cases of Covid-19 in fully vaccinated members of the New York Yankees organization: one player, three coaches and five team staff. The revelation has led to questions about vaccine efficacy and fears of super-strength variant strains. But experts say these cases show the vaccine is working, and testing remains a useful tool. A Major League Baseball spokesperson confirmed to CNN Wednesday that eight of those nine cases were asymptomatic. Each of the nine were fully vaccinated -- it had been at least 14 days since their single dose of the Johnson & Johnson Covid-19...