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Seniors taking cholesterol-reducing drugs, statins, might not be fully protected from the flu, two new studies suggested.

In the first study headed by Dr. Steven Black of the Center for Global Health at the Cincinnati Children's hospital, the researchers analyzed the medical records of about 7,000 people over the age of 65 from four different countries, including the United States. The people were all a part of the 2009-2011 clinical trial involving the flu vaccine.

The researchers had compared the number of antibodies that developed three weeks after the vaccine was administered. Antibody levels indicate how effective the vaccine is at protecting the body from the flu. The team found that people who took statins had 38 to 67 percent fewer antibodies than people who did not take statins.

"Apparently, statins interfere with the response to influenza vaccine and lower the immune response, and this would seem to also result in a lower effectiveness of influenza vaccines," Dr. Black concluded.

To combat the reduced effectiveness of the vaccine, the researchers argued that seniors taking statins might need a high-dose vaccine or boosters.

In the second study, Dr. Saad Omer, an associate professor at the Emory Vaccine Center in Atlanta, and colleagues examined the relationship between statins and the flu vaccine by analyzing data on about 140,000 patients with acute respiratory illness. The data were compiled from 2002 to 2011.

The researchers found that patients who were vaccinated and took statins had less protection against respiratory illnesses. One the key indicators that the researchers used to measure protection was inflammation. Statins tend to reduce inflammation in the body. However, when the body is being invaded, inflammation is often triggered by the immune system.

"A little bit of inflammation after vaccination is good," Omer concluded. "If you are on statins, the flu vaccine is slightly less effective."

"There is a clear-cut benefit to persons taking statins, so patients should not stop statin use because of the study results, even for a short time," Dr. Robert Atmar, a clinical research professor of infectious diseases at Baylor College of Medicine in Houston, who wrote a commentary to both studies, said. Atmar added that seniors on statins should not skip the annual flu vaccine either.

Experts noted that even though the studies' findings are interesting, more research should to be conducted to better understand the health risks for seniors who take statins. More studies could also pave way for better flu vaccines, particularly for seniors who have a higher risk of death from influenza.