Experts say regular flu shots tend to be only about 30 to 40 per cent effective in people 65 and older, who generally have weaker immune systems. Sanofi Pasteur's Fluzone High-Dose vaccine boosted that to 50 per cent.
"I wouldn't call it great" said Dr. Edward Belongia of the Wisconsin-based Marshfield Clinic Research Foundation, a flu vaccine researcher who was not involved in the Sanofi study.
But any improvement is welcome, and the results could mean fewer illnesses — and, hopefully, hospitalizations and deaths — in seniors, he said.
For other ages, effectiveness can run 60 per cent or higher for the regular vaccine.
The Food and Drug Administration licensed the higher-dose Sanofi vaccine in late 2009, based on a study that showed it led to higher levels of flu-fighting antibodies in seniors a month after vaccination. The new study is the first to measure how much protection it actually provides against the flu.
The study involved 32,000 seniors in the U.S. and Canada during the last two flu seasons. Half got a regular flu shot and half got the high-dose version. Researchers called the participants to see if they had flu symptoms or were hospitalized; tests to confirm the flu were done in more than half of the people reporting symptoms.
The high-dose shot was 24 per cent more effective than the regular shot at preventing flu, against all strains, the company said.
Sanofi has the only high-dose flu shot for seniors on the market. It was used last year in 1 in 5 seniors who got vaccinated, according to Sanofi. The $27 per dose cost is more than twice the $12 for the company's older version. But Medicare pays for both, and Sanofi executives say they don't think cost is a significant deterrent.
Instead, they believe doctors have been holding off until they saw real-world effectiveness studies.
Dr. David Greenberg, a Sanofi vice-president, is scheduled to present preliminary study results on Thursday at a meeting of vaccination experts in Atlanta. The Advisory Committee on Immunization Practices advises federal health officials, who then make vaccination recommendations to doctors.
The government already recommends flu vaccines for everyone, except babies under 6 months. The panel is expected to discuss whether to one day voice a preference for Fluzone High-Dose for seniors.
Among infectious diseases, flu is considered one of the nation's leading killers. On average, about 24,000 Americans die each flu season, according to the Centers for Disease Control and Prevention.