Publicity surrounding the pandemic of H1N1 swine flu probably drove people to clinics, the team at the U.S. Centers for Disease Control and Prevention reported.
Separately, Quest Diagnostics reported that H1N1 has almost completely displaced seasonal flu strains this year and still continues to be active in the U.S. south.
U.S. health experts are trying to get more Americans to seek flu vaccines every year. In an average year, influenza kills about 36,000 and puts 200,000 or so into the hospital.
Another reason for pushing vaccination -- the flu vaccine supply is uncertain, but if the market were more predictable, it would be easier for the flu vaccine makers and for the government to contract with them.
The United States licenses five influenza vaccine makers -- Novartis, AstraZeneca unit MedImmune, Sanofi Aventis, GlaxoSmithKline and Australian vaccine maker CSL.
The CDC officials looked at two large surveys covering nearly 80,000 children and 180,000 adults to find out how many got seasonal flu vaccines over the past season, starting in August, and who got H1N1 vaccines when they started trickling out in October.
Compared with the previous influenza season, 2009-10 saw a 67 percent relative increase in estimated coverage for children, and a 30 percent relative increase for adults aged 18-49 years without high-risk conditions, the CDC team wrote in the agency's weekly report on death and disease.
But this remains far below targets of 60 percent for adults and 90 percent of the over-65s, the CDC said.
40 PERCENT VACCINATED
Overall, a median of just over 40 percent of Americans got a seasonal flu immunization by January 31, the report found.
One successful experiment was vaccinating children in schools for H1N1. The CDC said state health officials might try using this approach more broadly for flu in general.
About 40 percent of children aged 6 months to 17 years got a seasonal flu vaccine for 2009-2010, compared to no more than 30 percent the year before, the CDC found.
In the coming flu season, a special high-dose flu vaccine will be available for people 65 and older, who have less active immune systems than younger people and who get less protection from normal flu vaccines.
Quest, which makes lab tests for flu, says H1N1 crowded out all other flu viruses over the season and continues to do so. H1N1 caused one wave of disease soon after it broke out last April and a second wave after school started in late August.
A third wave has not occurred in 2010 as evidenced by declining H1N1 testing and positivity rates, the company said in a statement.
Yet, during the four weeks ending April 15, 2010, about 26 percent of patients in all age groups tested in the southeast and 22 percent in the central south were positive for H1N1, compared to 6 percent for the remainder of the United States.