What you need to know after 9 members of New York Yankees test positive for COVID Vaccines are still effective Tags: NEW YORK – Nine members of the New York Yankees, including players and staff, have tested positive for coronavirus. All of them had been vaccinated with the single-dose Johnson and Johnson vaccine. The infections may cause some to question that vaccine’s effectiveness. The information submitted for its emergency use authorization indicated the Johnson and Johnson vaccine had a 66% efficacy against any symptomatic COVID, including mild illness. When you consider protection against moderate to severe COVID, the efficacy went to 72% in the United States. Against severe disease it was 85% effective.