Flu vaccines have a minimal effect on the prevention of influenza or its complications in the elderly, a new paper reveals.

The study, which was published this week by the Cochrane Review Group, an international consortium of scientists, found that flu shots are only 28% effective when given to people over 65. The Cochrane group analyzed data from patient studies on the flu vaccine performed around the world during the past 37 years.

Results were slightly better for nursing home residents. One reason is because residents receive regular medical surveillance, and tests can easily verify influenza infections.

“There is a wild overestimation of the impact of these vaccines in the community,” said Tom Jefferson, a leader of the project. “In the case of a pandemic, we are unsure from the data whether these vaccines would work on the elderly.”

Despite the results, the World Health Organization and the U.S. Centers for Disease Control and Prevention still recommend that elderly get flu shots.