As Maryland wraps up its worst flu season in three years, a small army of researchers is working on a vexing problem: why flu shots so often don't help the elderly.
No matter how many people are vaccinated and what recipe drug makers use to formulate the flu vaccine each year, it generally works in only 30 percent to 40 percent of those over 65 - compared with 80 percent to 90 percent of younger adults, experts say.
Doctors gauge a vaccine's effectiveness by examining blood levels of the antibodies our bodies produce after receiving it. They say older bodies have more trouble producing the antibodies than younger ones, even with a push from flu vaccine, so they're working on a more potent version of today's shots for older patients.
Flu has hospitalized at least 800 people in Maryland since the season began in October, about 30 percent of them children, according to state health officials. The season runs from October to May.
"This was a very active flu season," said Rene Najera, an epidemiologist with the Maryland State Department of Health and Mental Hygiene.
Maryland hospitals reported roughly 2,250 lab-confirmed cases in each of the two weeks after Feb. 10 - identified by the Centers for Disease Control and Prevention as the peak of this year's flu season.
This was the first year that the state's hospitals reported such figures, making comparisons with previous years impossible, Najera said. The number of flu cases began to drop sharply by mid-March, he said.
But nationwide, flu continues to take a heavy toll, hospitalizing 200,000 people each year, killing 36,000 and causing fever, fatigue, headaches and other symptoms for up to 20 percent of the population each year, according to the CDC. The numbers remain high despite more vaccinations each year.
Improvements are slow in coming because the flu virus is a constantly evolving target. The recipe for each year's vaccine is an educated guess based on the type of viral strains common in Asia at the close of the previous season.
Scientists believe the virus migrates to North America from the Far East. Overall, flu vaccine is usually 70 percent to 90 percent effective, but it was only 44 percent effective this year because the virus evolved a step beyond what international health experts expected.
"Strains for last year were expected to circulate again this year, but the virus mutated," Najera said.
