Up to 80 million Americans infected with H1N1: CDC

But 90 percent of the most vulnerable people remain unvaccinated, with only about 61 million Americans having received shots, the CDC said.

Swine flu vaccine is still widely available, with more than 130 million doses produced and 160 million people at high priority for getting the vaccine.

The pandemic, which began in March, is on the wane but health officials stress that influenza is unpredictable and could come back or mutate.

And this new virus, while it has not caused more deaths than seasonal influenza, has killed younger people than seasonal flu does.

About 90 percent of deaths in an average year are among people over 65, while 90 percent of those seriously ill or killed by the new virus are much younger and include as many as 1,730 children.

VACCINE STRUGGLE

Health experts say vaccination is by far the best way to ensure the virus does not come back or mutate into a new and more dangerous form, but the vaccine rolled out slowly and the public is now skeptical of the need to be vaccinated.

The U.S. government struggled for months to work with vaccine makers to get immunizations out. Now it is struggling to get rid of tens of millions of doses it purchased.

As of January 2, an estimated 20.3 percent of the U.S. population (61 million persons) had been vaccinated, including 27.9 percent of persons in the initial target groups and 37.5 percent of those in the limited vaccine subset, the CDC said in its report.

An estimated 29.4 percent of U.S. children aged 6 months to 18 years had been vaccinated. The CDC said this rate is similar to what is seen for seasonal influenza, which kills an estimated 36,000 Americans and up to 500,000 people globally each year.

More pregnant women than usual have been vaccinated -- 38 percent as compared to between 15 percent and 25 percent in an average year. Pregnant women are always at high risk from any flu and they accounted for an unusually high percentage of those sickened and killed by H1N1.

The results in this report show that nearly 90 percent of adults aged under 65 years with medical conditions that increase their risk for influenza-related complications remain unvaccinated,' the CDC added. These include otherwise healthy people with asthma or diabetes.

And just 22 percent of healthcare workers say they have been vaccinated, although they are more likely to be infected and can infect their vulnerable patients.

Five companies are supplying swine flu vaccine to the U.S. market -- Sanofi-Aventis, Novartis, AstraZeneca unit MedImmune, CSL and GlaxoSmithKline.