A better flu shot in the making to eliminate influenza

For the past four years, doctors’ offices, medical clinics and pharmacies have offered older adults high-dose versions of the annual flu vaccine.

The hope was that this alternative would better protect seniors, but scientific evidence proving its effectiveness has been lacking.

Now a study, published recently in the New England Journal of Medicine, finds that Fluzone High-Dose does indeed prevent influenza in older adults, reducing cases of the flu by 24 percent compared with the standard version. But some experts warn that it remains difficult to assess the effectiveness of flu vaccines generally in older patients.

Fluzone High-Dose contains four times the amount of antigen found in other flu shots. Previous research had indicated this boost produced a greater antibody response in recipients – significant because the immune response becomes less robust with age.

The U.S. Food and Drug Administration asked for more rigorous proof of effectiveness when it approved Fluzone High-Dose for those 65 and older on an expedited basis in 2009. The agency wanted evidence that the vaccine reduced the number of people who had influenza.

In the new study, scientists working for the manufacturer and at several universities compared 15,982 older adults who received the high-dose vaccine in 2011 and 2012 to 15,983 seniors who got the standard vaccine. The key finding was that 1.4 percent of the first group contracted the flu versus 1.9 percent of the second group.

“A lot of physicians have been waiting to see these results,” said Dr David Greenberg, the chief medical officer at Sanofi Pasteur and an author of the new study. Sanofi Pasteur has distributed nearly 21 million doses of Fluzone High-Dose since the vaccine was introduced in 2010, and in the coming flu season expects to exceed the 8 million doses sold in the 2013-14 season, Greenberg said.

The cost of the high-dose vaccine is $28.65 a dose, and Medicare covers one shot a year without a co-payment.

“We have no way of knowing how the high-dose vaccine worked versus no vaccine at all,” said Michael Osterholm, the director of the University of Minnesota’s Center for Infectious Disease Research and Policy.
The authors said that the standard vaccine prevents the flu about 50 percent of the time in older adults.

But that figure comes from 1994 research that has been shown to be biased and unreliable, Osterholm said.
Some evidence comes from the Centers for Disease Control and Infection. In the 2012-13 flu season, the agency found the standard flu vaccine was effective 27 percent of the time for those 65 and older. In the 2013-14 season, effectiveness was 52 percent in the older population.

Another concern relates to the small portion of older adults who came down with the flu in the new study: less than 2 percent. “We have probably substantially overestimated how much influenza contributes to deaths in the older population and how much improvement occurs due to vaccination,” Osterholm said.
The CDC nonetheless continues to recommend annual flu shots for all older adults, and there is no evidence that the high-dose vaccine causes unusual side effects.