T

he widely used class of cholesterol-lowering drugs known as statins may undermine the effectiveness of flu shots, new studies suggest, a finding that could complicate care for older adults.

Two research groups reported Thursday that people who take statins appear to benefit far less from influenza vaccinations than those who do not. The effect is particularly marked among people taking synthetic statins — fluvastatin (Lescol) is an example — rather than naturally produced varieties of the drugs.

Many older adults use statins and also get flu shots because they are especially vulnerable to complications from a bout of influenza. That makes it critical to figure out if the drugs are eroding the modest protection the flu vaccine offers older populations, the researchers and outside experts said.

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“It’s new information that really wasn’t on our radar,” said Dr. Edward Belongia, an influenza vaccine expert at Marshfield Clinic Research Foundation in Marshfield, Wis.

Belongia, who was not involved in the research, said more study was needed, and quickly.

“Based on what we see so far, we should be reasonably concerned that there could be a real effect here,” he said.

If statins do dampen the levels of antibodies generated by the flu vaccine, it will be important to see if the effect carries over to other vaccines recommended for seniors, including one to prevent pneumococcal pneumonia.

The possibility that statins interfere with the vaccine makes sense biologically, influenza experts Dr. Robert Atmar and Dr. Wendy Keitel of Baylor College of Medicine in Houston, acknowledged in a commentary that was published alongside the studies in the Journal of Infectious Diseases.

In addition to lowering LDL, or bad cholesterol, statins have a broad effect on the immune system. For that reason, groups have been studying whether the drugs could be used to treat influenza.

The researchers behind these studies knew of that work and wondered if the drugs were in effect a double-edged sword: useful to modulate the body’s response to influenza infection but unhelpful if taken when the body is prompted — through vaccination — to generate antibodies against flu viruses.

One of the studies was conducted by researchers at the Emory Vaccine Center at Emory University in Atlanta. The second was led by Dr. Steven Black, a pediatric infectious diseases specialist at Cincinnati Children’s Hospital; Black’s coauthors are researchers who work for Novartis Vaccines.

Novartis makes a flu vaccine for seniors — not yet licensed in the United States — that contains an adjuvant, a compound that amplifies its effect. Black has worked as a consultant for Novartis and other vaccine makers.

Both studies have limitations. One of the groups mined data generated for other purposes to see if there was evidence statins eroded the protection flu vaccine induces. When data are used to answer questions not considered in the original study design, there is always the possibility that factors that could bias the results are not adequately addressed.

But Black said the fact that two groups reached similar conclusions makes him feel more confident about the finding.

Black’s study looked at influenza antibody levels generated by people who were vaccinated with regular vaccine and the adjuvanted variety. When the researchers looked at the results for study participants who were taking statins, they saw sharp drops in the levels of antibodies generated.

The Emory study looked at the effectiveness of flu vaccine in preventing people from getting sick with a respiratory illness that required medical attention.

They found more illness in vaccinated people who were taking statins than those who were not.

Black takes a statin drug. Because of the concerns raised by the new research, he asked for a high-dose vaccine when he got his flu shot this year, he said in an interview with Stat.

But the lead author of the Emory study, Dr. Saad Omer, said it is too soon to recommend doctors try to act on these findings.

If statins do interfere with the flu vaccine, researchers would need to figure out whether taking people who were due to get a flu shot off statins — and for how long — would solve the problem.

“My bottom line is that this is an interesting signal,” Omer said. “The next step should be prospective studies confirming our findings.”

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