The influenza vaccine that many Americans clamored for this year was not very good at protecting people against influenza, colds and similar viruses, a preliminary report published on Thursday shows.

The study is the first attempt to show whether the vaccine that many sought after a flu scare this autumn and winter actually worked.

The study of hospital workers in Colorado, a state that was hit early and hard by influenza, showed the vaccine had “no or low effectiveness against influenza-like illness,” the U.S. Centers for Disease Control and Prevention said in its report.

Many experts did not expect the vaccine to work well, although the CDC had hoped it would at least prevent some of the worst illnesses caused by this year’s strain of influenza.

The vaccine is only meant to protect against true influenza. Without a test, it is often difficult to distinguish between influenza and other, similar viruses.

CDC spokesman Tom Skinner said that for this reason the report only shows part of the story.

“This is the first of a number of studies that we are going to do to try to answer the question, ‘did this year’s vaccine offer protection against flu?’ This study in and of itself does not answer this question,” he said in a telephone interview.

However, the study shows that people who were vaccinated against influenza came down with colds, flu and similar viruses at the same rate as people who were not vaccinated. This would presumably include true influenza.

The vaccine is formulated each year in February or March, at the end of the northern hemisphere’s flu season, and did not include the Fujian strain of influenza, a new, mutated strain that turned out to be the predominant type of flu in the United States and several other countries this year.

The epidemic appears to be on the wane — this past week only 2.8 percent of hospital visits were for influenza-like illnesses, compared to 5.5 percent the week before.

News coverage of the early start to the flu season sent many people rushing to get vaccinated. There were shortages in some places and the U.S. government bought 625,000 doses of flu vaccine from makers Chiron and Aventis .

More here.