Officials said Thursday it's believed that Dr. William Vitale improperly mixed the 2013 seasonal flu vaccine with routine childhood immunizations in some cases, which may have impacted the efficacy of the flu shot.
Parents of the 27 patients are being called and advised to have their children re-vaccinated.
"There is a different level of urgency," said Dr. Robin Taylor, medical officer of health for the Capital District Health Authority.
"With us being in flu season, it's really important that those parents, as soon as possible, are made aware of the situation and are able to get their children re-immunized."
Last month, the provincial Health Department said it was investigating Vitale, a private physician, after he allegedly administered improperly mixed vaccinations for about 500 children under the age of two between 1992 and 1994, and between 2003 and the present.
Taylor said at least four of the 27 children who received flu shots are among the approximately 500 patients who were given the other mixed vaccines.
The investigation was launched after the Health Department received a complaint from a member of the public on Dec. 3. The College of Physicians and Surgeons of Nova Scotia was told of the complaint and suspended Vitale's medical licence on Dec. 13.
Taylor said the approximately 500 patients were being contacted and advised to be re-vaccinated to protect them from a long list of preventable diseases, including measles, mumps, tetanus, whooping cough, diphtheria, polio and rubella.
"Vaccines in Canada and around the world are manufactured very carefully and tested very carefully not just for what's in them but also how they're given," said Taylor. "The two vaccines may interact with each other in such a way that the body doesn't respond as strongly as it needs to."
She said there is no evidence that any of Vitale's patients have become ill from the mixed shots.
Taylor has said Vitale was also accused of improperly mixing vaccinations for seven patients in a similar incident in 2006. Those patients were re-vaccinated and Vitale was told to stop the practice.
Officials say their investigation into Vitale's records is ongoing, and the number of patients affected may change. Taylor encouraged any of Vitale's patients, regardless of age, who know they received a mixed vaccination to be re-immunized.
Vitale could not be reached for comment at either his office or home.
Meanwhile, officials said a re-vaccination clinic for patients who do not have a family doctor has received more than 100 calls from patients and booked dozens of appointments since it opened Wednesday.