Immunization rates for flu shots have remained relatively flat during the past decade, prompting concern among some health officials.

Despite an aggressive awareness campaign to increase the number of people getting flu shots, the Centers for Disease Control and Prevention (CDC) say far too many people — including infants as young as 6 months old — are not getting vaccinated.

In its latest report, the CDC found that just 47 percent of all people 6 months of age and older in the United States had received a flu shot during the 2014-15 flu season, up about 1 percent from the prior year.

Almost 75 percent of babies between 6 months and 23 months of age were vaccinated at least once against the flu last year. That rate has steadily increased for more than a decade.

CDC officials say that still leaves millions of those most vulnerable to the illness at risk.

More disturbing to health providers is that fact that only about 68 percent of kids between 2 and 4 years of age were given a flu shot and the immunization rate for children between 5 and 12 (62 percent) and 13 and 17 years of age (47 percent) remained essentially flat.

Among adults, almost 44 percent received a flu vaccination last year, up 1.4 percent from 2013-14.

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CDC officials say children less than 5 years of age, and particularly those younger than 2 years of age, are at high risk of a variety of serious flu-related complications.

About 20,000 children under the age of 5 are hospitalized each year in the U.S. for influenza-related complications ranging from pneumonia, dehydration, sinus problems, and ear infections.

They report that 147 children died from influenza last year. Last month, Kiera Driscoll, a 5-year-old Las Vegas kindergartner, whose parents said she was given a flu vaccine, went into cardiac arrest and died after coming down with influenza and pneumonia.

Health officials say Driscoll’s death represents a rare instance that should not dissuade parents from having their children – and themselves – vaccinated against one of the world’s most common and potentially deadly diseases.

In 2010, the U.S. Department of Health and Human Services, through its Healthy People 2020 health-promotion and disease-prevention program, set out to achieve a 70 percent vaccination rate for children between 6 months and 23 months.

“[The flu vaccination rate] was really bad back in 2003, but in 2004 the Advisory Committee on Immunization Practices introduced the recommendation to vaccinate the 6-to-23 months’ population and rates have gradually climbed since then,” said L. J. Tan, PhD, chief strategy officer for the Immunization Action Coalition. “That said, I believe we still are not where we need to be.”

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So, why are so many adults opting not to immunize themselves and their children against the flu?

CDC officials and immunization advocates say it’s because of unfounded fears based on myths, ignorance, and the age-old fallacy that something like this could never happen to them.

CDC researchers say parents who don’t vaccinate their children against the flu seem to fall mostly into two camps. There are those who say the vaccine was not promoted or recommended by their child’s physician. And there are those who simply believe that their child isn’t susceptible to the flu because their kid is otherwise healthy and does not have a high-risk condition.

Unsubstantiated campaigns promulgated by celebrities such as actress Jenny McCarthy, suggesting a correlation between the routine battery of immunizations given to children and the rising rate of autism diagnoses have given uninformed parents another ready excuse, officials say.

“Despite so much evidence now to the contrary, the myth that vaccines can cause autism still circulates,” Tan told Healthline. “And, we still have members of mainstream press making statements that continue to suggest some form of controversy. There really is no controversy anymore and we should stop saying that there is.”

Officials at Autism Speaks, a leading autism advocacy organization that sponsors autism research and conducts awareness and outreach activities, concur.

“Over the last two decades, extensive research has asked whether there is any link between childhood vaccines and autism,” the organization said in a statement. “Scientific research has not directly connected autism to vaccines. Efforts must be continually made to educate parents about vaccine safety. If parents decide not to vaccinate, they must be aware of the consequences in their community and their local schools.”

Dr. Cindy Weinbaum, acting deputy director of the CDC’s Immunization Services Division, told Healthline that vaccinating children according to the recommended schedule is “one of the best ways to protect them from 14 harmful and potentially deadly diseases” before their second birthday.

“Specific to influenza, a yearly vaccine is the single best way to protect children from the flu,” she said. “While flu vaccination uptake among children has increased, there is still a long way to go to protect every child.”

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This appears to be especially true among African-American and Hispanic populations.

In its latest data, the CDC found that only about 44 percent of African-Americans and Hispanics older than 6 months of age were vaccinated against the flu last year.

These numbers are below the immunization rates for whites (48 percent) and Asians (51 percent).

There are also significant disparities by state.

Among children between 6 months and 17 months of age, Montana had the lowest immunization rate at about 45 percent while Rhode Island led the pack at almost 79 percent.

For adults, Nevadans were most willing to roll the dice and take their chances. They checked in with a national-low flu-shot rate of 36 percent. South Dakota topped the list at 58 percent.

“We have a very safe vaccine that works and so we feel that [people] should not be gambling with influenza vaccination,” Tan said. “Why take a chance that this is the year that your choice not to get your child vaccinated because you heard it was a mild season? We don’t do that with car seats.”