The Centers for Disease Control and Prevention (CDC) reported that this year’s flu vaccine had "no or low effectiveness" against influenza or influenza-like illness. Depending on how the data were analyzed, the vaccine protected from zero percent to 14 percent of study participants.
In the study, a questionnaire was sent out to 3,100 health care workers asking whether they had received the flu vaccine and whether they had contracted the flu or flu-like symptoms, and 1,886 people responded. The study was the first of its kind to be conducted by the CDC.
However, some say the study had limitations, for instance only 61 percent of the health care workers responded to the survey, and participants reported whether or not they had the flu based on their own observations, not lab testing.
Researchers say additional studies are needed to evaluate the effectiveness of this year’s flu vaccine against laboratory-confirmed flu and flu-related complications, including hospitalization and death, and they hope further studies will show more favorable results for the vaccine.