(CNN)Eight members of the New York Yankees have tested positive for coronavirus this week despite being inoculated with the Johnson & Johnson vaccine, the baseball team said Thursday.
The eight infected Yankees include coaches, staff members and a player. Seven do not have symptoms, said Jason Zillo, the team's vice president of communications.
The Yankees said the eight infected members received the Johnson & Johnson vaccine at least two weeks ago.
The single-dose Johnson & Johnson vaccine was 72% effective against Covid-19 among US trial participants and 85% effective against severe Covid-19. The two-dose vaccines used in the US, from Pfizer/BioNTech and Moderna, are both about 95% effective.
It's not possible to get Covid-19 from any of those three vaccines because none of them contains coronavirus.
But if someone does get Covid-19 after being fully vaccinated, the symptoms will likely be far less severe than if they didn't get vaccinated at all, said Dr. Jonathan Reiner, professor of medicine and surgery at George Washington University. This is similar to how flu vaccines work.
And the fact that almost all of the infected Yankees don't have symptoms shows how "remarkably great" the vaccine is at preventing people from getting sick from Covid-19, Reiner said.
Of the eight team members who tested positive, only one -- third base coach Phil Nevin -- showed symptoms, Zillo said. He said Nevin is now feeling better.
The seven asymptomatic people who tested positive this week include staff members and shortstop Gleyber Torres.
Torres had tested positive in December but had since tested negative, the Yankees said.
There have been reports of "breakthrough" infections among vaccinated people, but they represent a small fraction of the more than 117 million people in the US who are fully vaccinated.
In those cases, "the resulting infection is more likely to have a lower viral load, may be shorter in duration, and likely less risk of transmission to others," said Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention.
And people are still vulnerable to infection immediately after the shots because the vaccines don't fully kick in until about two weeks after the last dose.
The Yankees have been playing under relaxed health and safety protocols after reaching an MLB-recommended 85% threshold of vaccinated team members in late April.
On Thursday, the New York State Department of Health said it's been in contact with Major League Baseball and the Yankees.
"While there have been anecdotal reports of New Yorkers who have had a positive COVID test 14 or more days after receiving their last vaccine dose, DOH is investigating those cases along with the ones linked to the Yankees further to determine if they meet the formal CDC definition of vaccine breakthrough," the health department said a statement.
The Yankees were in Florida on Thursday for the last game of their series against the Tampa Bay Rays.
They're scheduled to travel to Baltimore ahead of their series against the Orioles on Friday.
