There are growing concerns about so-called “breakthrough” cases of COVID-19 – infections that happen after a person has been immunized against the virus.

Several members of the New York Yankees organization contracted the virus, even though they were believed to be fully immune.

Dr. Shobha Swaminathan, an infectious disease specialist at Rutgers New Jersey Medical School, says that the COVID-19 vaccine overall is effective at preventing the virus and preventing serious illness. And while breakthrough cases may look concerning, she says that they prove that the vaccines are working.

“This is really why we should get vaccinated so that even if you get exposed, you will have a very mild infection as opposed to a year ago,” Swaminathan says. “We probably would have seen people getting a lot sicker if they got exposed without the vaccine."

Swaminathan says that in the case of the Yankees, it is important to note that most of the positive cases were asymptomatic.

“The vaccines did what they were supposed to do; they prevented these players from feeling sick and having serious complications based on what we know thus far,” Swaminathan says.

Doctors are currently keeping track of the cases of fully vaccinated patients who tested positive for the virus out of caution.

“Whenever we have infections develop in any patient who has been vaccinated previously, most of us are analyzing the strains and sending them to the [Centers for Disease Control and Prevention] to see if there are any variants we should be concerned about,” Swaminathan says.

Swaminathan says that Americans should still get vaccinated, and said that the common concerns she hears among patients are regarding the side effects of the vaccine, like fevers or arm soreness. She says that while those symptoms may appear scary for some, it is important to know that the symptoms are generally mild and they should only last a short while. There are no reports of lasting side effects from the vaccine.

Swaminathan said breakthrough cases are rare, and if a person who's been fully vaccinated tests positive, they are less likely to become very sick.