MONDAY, Dec. 5 (HealthDay News) -- U.S. health officials used Monday, the start of National Influenza Vaccination Week, to urge Americans to get their flu shot before the season begins in earnest.

Since the H1N1 flu pandemic of 2009, vaccination rates have increased for some people, especially pregnant women and children -- the two groups hit hardest hit by the pandemic. Right now, vaccine supplies are ample, but they could start to dwindle over the next few weeks, so officials are hoping more people will get their shot before Christmas.

"Flu vaccination is the essence of prevention, and prevention is the essence of public health," Dr. Howard Koh, assistant secretary for health at the U.S. Department of Health and Human Services, said during a midday news conference.

The H1N1 flu outbreak led to a greater awareness of flu and the importance of vaccination, Koh noted. However, awareness and action are two different matters, he stressed.

"Flu remains a serious and unpredictable disease," Koh said. "Each year in the U.S. an estimated 5 to 20 percent of the population may be infected and more than 200,000 may be hospitalized during the flu season."

A flu shot is recommended for everyone aged 6 months and older, Koh said. The vaccine is particularly important for those at the highest risk of complications from the flu, including young children, pregnant women, seniors and people with chronic health conditions such as asthma, diabetes and heart or lung disease, he said.

"More than 130 million Americans have at least one chronic condition," he said, adding that serious complications from the flu can include dehydration, pneumonia and death.

Health care workers especially need to get vaccinated to protect their patients, their families and themselves, Koh said.

Before the H1N1 flu pandemic, only about 15 percent of pregnant women got a flu shot. "Last season, almost half of pregnant women were vaccinated," Koh said. "Also, last year about half of our nation's children were vaccinated, and we saw no racial/ethnic disparities in vaccination coverage among minority children."

The U.S. Centers for Disease Control and Prevention did a survey last month to gauge how many people were getting vaccinated. For health care workers, the rate was 63 percent, a 7 percent increase over this time last year, Koh said.

Flu activity so far has been light, officials said, but that could change quickly, given the unpredictable nature of the disease.

"We are seeing only a little flu across the country right now, but that doesn't mean it isn't right around the corner," Dr. Anne Schuchat, director of National Center for Immunization and Respiratory Diseases at the CDC, said during the news conference.

Thirty states have already reported cases of flu, she said, but flu season typically peaks in January and February. That's why it's a good time to get vaccinated now, before the flu season kicks into high gear, she added.

As of the first week in November, the CDC estimated that 36 percent of people 6 months of age and older had gotten a flu shot, Schuchat said. That's about 111 million people -- about 3.5 percent higher than last year, she said.

Although the number of adults who were vaccinated in November was about the same as last year, more children were vaccinated this year, Schuchat said. An estimated 62 percent of people aged 65 and older had been vaccinated as well, she added.

But, among those with chronic conditions, only 42 percent had been vaccinated by early November, Schuchat said. "That's very close to what we had seen last year," she noted.

Schuchat thinks many more people have been vaccinated since the survey, and others will get vaccinated as the season progresses. This year's vaccine is the same as last year's and seems to be a good match for the flu strains that are circulating so far, she said.

However, that doesn't mean that last year's shot will still protect you, Schuchat said. To be safe, she recommends getting vaccinated again this year.

Schuchat cautioned that vaccine supplies could start to run low. So far, 129 million doses of vaccine have been distributed, which she called a typical amount.

"We believe supplies are still ample around the country, but we really don't know how long that's going to last," she said. "We hope people will be able to find flu vaccine easily in the weeks ahead, but we hope you can act soon. The supply of flu vaccine this time of the year is pretty much fixed [by the manufacturers], and vaccine will likely become harder to find and get."

More information

For more on flu, visit the U.S. Centers for Disease Control and Prevention.