Dr. Jorge Parada, medical director of the Infection Prevention and Control Program at Loyola University Health System near Chicago, said many say they got the flu from the vaccine.
"It is not true to say that the flu shot can give someone the flu," Parada said in a statement. "Remember, it takes two weeks from vaccine injection for a person's protective immunity to become effective. Thus, if a person gets exposed to the virus right around the time he or she gets the vaccine, they may experience the flu during that window before the vaccine has time to kick in. In these cases, it is not the flu shot that gave the person the flu, but rather that they did not get the flu shot early enough to be protected when they were exposed and infected by the flu virus."
Parada noted that there are many varieties of flu, and depending on which vaccine you get, it will target the three or four dominant strains.
"People might not know that typically three to four dominant varieties of flu circulate every season," he said. "As a result, people can get the flu several times within a season, but they are actually getting different varieties of the flu -- all the more reason to get the flu shot!"
Many also think last year's flu shot will protect for another year.
"The vaccine is effective for one flu season, so everyone needs to get the vaccine every year," Parada advised. "People with chronic conditions may be advised by their physician to get a second flu booster later in the season to provide best protection."
Some people mistake the stomach flu with influenza.
"The flu is a respiratory illness and rarely are nausea, diarrhea and vomiting the main symptoms," Parada said. "People may have diarrhea and other stomach upset, and it may be from a virus infection, but it is unlikely to be from the flu virus."
Loyola is in its fifth year of mandatory flu vaccination for employees, students, volunteers and vendors and uses advanced technology to accurately identify 17 viral and three bacterial pathogens in about 60 minutes in the lab.