THURSDAY, Jan. 15, 2004 (HealthDayNews) -- This winter's version of the flu vaccine does not provide much protection against influenza-like illnesses such as sore throat and the common cold, a small, preliminary study shows.
And it's too early to say how effective the vaccine is against the flu itself, according to experts at the U.S. Centers for Disease Control and Prevention.
The CDC is still urging flu vaccination, especially for such high-risk persons as children and older people, because history shows that the vaccine probably is preventing the disease in many cases and reducing the incidence of complications in those who develop the disease, says Dr. Nidhi Jain, a CDC epidemiologist.
However, she adds, the effectiveness of the vaccine is being determined in a series of studies across the country.
"Those studies are ongoing now, and we will have results later on this spring," Jain says.
The study of the vaccine's effect on flu-like illnesses, reported in this week's CDC publication Morbidity and Mortality Weekly Report, was done in Colorado last month. It asked 1,881 workers at the Denver Children's Hospital, 78 percent of whom had gotten the flu shots, whether they had experienced flu-like illnesses, with fever, cough or sore throat.
The vaccine protected only 14 percent of those who got it against those illnesses, the epidemiologists report.
"We did not look at the incidence of influenza or of complications of influenza in this study," Jain says. "We will have to look at all the studies being done to get that information."
The CDC acknowledges that the current vaccine is "a suboptimal antigenic match" against the most prevalent strains of this winter's influenza, which changes constantly. Each year, scientists must determine exactly which strains should go into the vaccine, to keep up with the constant changes that enable the virus to elude the body's immune defenses.
It is an admittedly imperfect art, says Dr. John J. Treanor, director of the Vaccine Evaluation Unit at the University of Rochester in New York state.
Strains of the flu virus are named after the areas where they were first located. This winter's most prevalent strain has turned out to be A/Fujian, which differs from last year's A/Panama, the basis of the current vaccine.
"Protection against the Fujian strain is not optimal," Treanor says. But the mismatch is not much different than has occurred in previous years, and it still is advisable for unprotected people to get the vaccine, he says.
"Remember, there are three different strains in the vaccine," Treanor says. "One of those strains could pop out later this year.
And the record of past years in which there was a mismatch between the virus used for the vaccine and the most common strain in the population shows that the vaccine did reduce the number of infections and the potentially life-threatening complications in those who developed influenza, Jain says.
"We still recommend that people get the vaccine, especially those at high risk of the complications of influenza," she says.