The flu vaccine this year is less effective than vaccines in previous years, researchers have found.

Scientists at the University of Minnesota found that the most common flu vaccine in the United States is only effective in 59 percent of health adults. Previous reports said the vaccine was 70 to 90 percent effective.

The Centers for Disease Control and Prevention recently recommended Americans begin getting the flu shot now. Flu shots are recommended for anyone over the age of six months.

The study results were based on 5,707 vaccine studies published in the last 40 years. Researchers then narrowed their analysis down to 31 studies that tested for the presence of flu in lab tests instead of just counting an increase in flu antibodies.

The results showed that a newer type of vaccine that uses a live virus was 83 percent effective in protecting children from flu but the vaccine is currently not recommended by the CDC group on immunization.

Study results were published in the Lancet Infectious Disease journal.