1 in 5 children have vaccine-wary parents, which may affect future immunization campaigns

(CNN) One in five children in the United States had a "vaccine hesitant" parent last year, according to new research from the US Centers for Disease Control and Prevention.

Parental concerns over vaccine safety have contributed to several major outbreaks of preventable diseases in the US and other countries in recent years. The 2019 measles outbreak in the US -- the largest number of cases in 27 years -- was largely driven by parents in New York and Washington statewho failed to follow childhood vaccine guidelines.

Outbreaks in the US of mumps and pertussis, or whooping cough, have also occurred in recent years due to a lack of basic childhood immunizations, while yearly flu vaccinations among children are much too low, according to the CDC.

Connection to Covid-19?

On a larger level, experts are concerned that vaccine hesitancy may also impact the ability of the US and other nations to control the coronavirus pandemic.

Pollng varies, but an online poll by the Associated Press/NORC Center for Public Affairs in May found half of Americans would refuse or hesitant to take a Covid-19 vaccine, while a study by King's College London found a similar response in the UK. In May, about a fourth of the French population said they would refuse to take a vaccine.

"You have a lot of folks who are very concerned about injecting a foreign substance with potential preservatives and things like that into the body, something that's very unnatural," said Dr. Henry Wu, an associate professor of infectious diseases at Emory University School of Medicine in Atlanta, who was not involved in the study.

"The irony is vaccines are really a way to train your body to fight off infections naturally," said Wu, who directs the Emory TravelWell Center.

"Vaccines are your best way to go, because imagine what happens when you get really sick with one of these viruses and you end up in the hospital with all kinds of things being infused through your body," Wu said.

Public health officials are concerned that vaccine hesitancy will impact the willingness of parents to allow their children to be vaccinated against Covid-19 when a safe and effective vaccine becomes available.

Because children under five appear to be significant carriers -- holding between 10 and 100 times more coronavirus genetic material in their noses than older children and adults for weeks without symptoms -- avoiding a vaccine could have significant consequences.

Over 900,000 cases of Covid-19 have been confirmed in children, according to numbers tracked by the American Academy of Pediatrics. Because most children appear to have few or no symptoms, case counts in kids are thought to be widely underreported.

First use of new model

The new research, published Monday in the Journal of Pediatrics, was led by epidemiologist Tammy Santibanez of the CDC's National Center for Immunization and Respiratory Diseases.

Santibanez and her team said it was the first report on prevalence of vaccine hesitancy among parents of children between six months and 17 years using a survey module developed by the center.

The questions were designed to measure concern over all types of childhood immunizations, not just the influenza vaccine. Vaccine hesitancy was defined as "the mental state of holding back in doubt or indecision regarding vaccination."

Parents with more concerns about the number of vaccines and side effects were more highly educated, and more likely to say they personally knew someone that had experienced a vaccine side effect, the study found. They were also more likely to say they did not consider their child's doctor to be "the most trusted source of information about vaccines."

Vaccine-hesitant parents were also more likely to have children under the age of six or be the parents of three or more children. Those parents were more likely to be concerned about long-term side effects of vaccines, the study found.

However, parents in the highest income group were less likely to be hesitant about vaccines or concerned about long-term side effects.

Responses in vaccine concerns varied widely by state. For example, only 12.9% of parents in Vermont were "somewhat to very hesitant," compared to to 25.4% in Mississippi.

The report also compared the number of children getting a flu shot in 2019 to the parent's degree of concern over vaccines. Children of vaccine-hesitant parents were 26% less likely to be inoculated against influenza than children of parents who were not concerned about vaccine safety.

"However, even among children of parents who reported being vaccine hesitant, 34% to 47% were vaccinated against influenza," the report said.

A historical concern

The report found the most hesitancy about vaccines, as well as concern about immunization schedules and serious side effects, were found among parents of Black children.

Nearly 30% of Black parents said they were hesitant about childhood shots and concerned about potential side-effects compared tothe percentage of White parents concerned about childhood shots (17.5%) and potential side effects (19.9%). Over 22% of Black parents were concerned about the number of shots a child was given at one time compared to 18.0% of White parents.

Concerns by Black and brown people about vaccinations of any kind have long persisted in the US, fed by such tragedies as the infamous Tuskegee case, a 40-year experiment in which Black men were not told they had syphilis or given sufficient treatment for their condition.

Between 1909 and 1979, there were reports that people with Mexican-sounding names were forced into sterilization procedures in California.

Recent social unrest, racial violence and police injustice and health care disparities contribute to the distrust that is common among people of color, said Harriet Washington, author of "Medical Apartheid: The Dark History of Experimentation from Colonial Times to the Present."

"African American people get treated differently. They have less access to doctors. When they describe their symptoms, they are not believed as often as Whites are. Medical technology is withheld from them. All of these things are a matter of record," Washington told CNN Senior Medical Correspondent Elizabeth Cohen recently.

There is a significant challenge ahead, Wu said, pointing to the behavior he sees in his travel clinic dedicated to providing vaccines to the public.

"I know from my experience running a vaccine clinic that most folks aren't going to run to get a vaccine," Wu said. "A lot of education is important. A lot of faith in the process is important. And then just fighting the misinformation -- the amount of misinformation that's already out there is enormous, and also the amount of distrust in many of our public health institutions is high.

"Developing a Covid vaccine may be the easiest step," Wu said. "You can have a 100% effective vaccine, but if only 30% of the people take it it doesn't accomplish a lot."