Some parents have adopted alternative vaccination schedules, but experts say this can pose serious consequences for their children’s health.

More parents are choosing to use alternative vaccine schedules for their children.

However, experts agree that this practice is not just irresponsible — it’s dangerous.

Alternative vaccine schedules are schedules that differ from those proposed by the Centers for Disease Control and Prevention (CDC) and American Academy of Pediatrics (AAP).

They have predominantly emerged in the past 10 years as part of the growing conversation surrounding autism and other claimed side effects from childhood vaccinations.

Learn more: Vaccines don’t cause autism — so what does? »

The popularity of alternative vaccine schedules is largely attributed to Dr. Robert Sears, the son of well-known pediatrician William Sears who published more than 30 books on parenting.

In 2007, Sears published “The Vaccine Book: Making the Right Decision for Your Child.”

In the book, Sears proposed two alternative vaccine schedules that parents could use if they were uncomfortable using the one established by the CDC.

His book opens a “middle ground” to parents who are leery of vaccination by creating a more gradual immunization schedule, spacing out certain vaccines from one another.

He says this alternative schedule lowers the potential for “chemical overload,” which may in turn lead to negative side effects, such as autism.

Every expert contacted by Healthline — including members of the CDC and the AAP —denounced Sears’ theories.

“Infants and young children who follow immunization schedules that spread out shots — or leave out shots — are at risk of getting sick,” said Dr. Allen Craig, deputy director of the CDC’s National Center for Immunization and Respiratory Disease.

“Several vaccine-preventable diseases remain common in the United States, and children may be exposed to these diseases during the time they are not protected by vaccines,” Craig added. “This places them at risk for serious illness that might cause hospitalization or death.”

Read more: The debate over vaccine safety is far from over »

At issue for many parents is the quantity of inoculations that are given to babies.

Infants will get 14 different vaccines and 26 inoculations by age 2 — sometimes receiving up to 5 shots in a single visit.

Sears did not respond to Healthline’s request for an interview, but he has discussed his recommendations in the past.

“I see a lot of parents questioning the CDC vaccine schedule. They worry that it’s too overloaded,” Sears told PBS Frontline in 2015.

“There’s too many shots at too young of an age and parents simply are looking for a safer way to do it, something they’re more comfortable with,” he said.

Sears warns that “chemical overload” can result from ingredients such as preservatives found in vaccines, or by the antigens (the germs used to provoke the immune response) themselves.

He still lists the preservative thimerosal, a mercury compound linked by some critics to autism, on his website.

However, due to public outcry, the CDC removed thimerosal from children’s vaccines in 2001 — even though no scientific research has linked the chemical to autism.

As for the potential risk from the antigens themselves harming a baby, the CDC states that babies are exposed to more antigens on a daily basis than they are from inoculations.

“Even if babies receive several vaccinations in one day, vaccines contain only a tiny fraction of the antigens that they encounter every day in their environment,” the CDC says on its website.

Read more: Anti-vaccination forces may get boost in Trump administration »

Sears says he has taken a more “logical” look at scheduling.

The hepatitis B vaccine, for example, is normally administered when a baby is born. Sears says that because it’s a sexually transmitted disease, an infant has a low likelihood of contracting it.

He proposes that inoculation be done later, around preschool age when the child is more likely to be exposed to blood or bodily fluids.

That may sound reasonable. The problem, experts say, is simply that there is a complete lack of scientific evidence to back up Sears’ theories.

“There are no data to suggest that alternative vaccine schedules are more effective, immunogenic, or safer. These are untested and empiric approaches,” said Dr. Kathryn Edwards, director of the Vanderbilt University Vaccine Research Program, speaking on behalf of the AAP.

“The academy espouses the schedule that has been tested and approved by the FDA,” she said.

Read more: Doctors debate treating unvaccinated kids »

Sears’ proposed schedules have led, in part, to a growing phenomenon known as “vaccine hesitancy.”

Vaccine hesitancy is different from the anti-vaccine movement, whose members reject the use of vaccines based largely on the discredited theory that they are linked with the development of autism.

The World Health Organization describes vaccine hesitancy as a “delay in acceptance or refusal of vaccines despite availability of vaccination services.”

An AAP report in 2016 revealed that between 2006 and 2013, the number of pediatricians who encountered parents that refused a vaccine increased from 75 percent to 87 percent.

The proportion of parents who refused one or more vaccines for their children also increased, from 9 percent to almost 17 percent.

“When parents choose to use an alternative vaccine schedule or delay vaccines, they are in essence performing their own risk assessment,” Cynthia Leifer, PhD, an associate professor of immunology at Cornell University, told Healthline.

“Unfortunately, their perception of the risks and benefits is not based on solid scientific and safety research,” she said.

Read more: Vaccination rate lower for children in military families »

Experts say that the vaccine schedule established by the CDC is not static. It continues to change based on new research and the development of new and better vaccines.

Sears’ theories are not criticized because they offer an alternative. Experts say they are criticized because there is currently no proof that his theories are helpful.

“The vaccine schedule has evolved over many decades and has been studied carefully and has been evaluated by the FDA. We really feel that the best approach is to use approaches that have been shown to be scientifically sound,” said Edwards. “What guides our approach is science, not empiricism.”

Every expert contacted by Healthline emphasized that using a delayed or alternate schedule jeopardizes the safety not only of individual children, but of the larger community.

As Healthline reported recently, an uptick in measles in Europe is just one of the many consequences of a decreased vaccination rate.

“By not vaccinating on schedule, parents are risking their children’s health. If a parent delays vaccines, their child is not protected,” said Leifer.

“Even worse, the youngest children are the most vulnerable for both getting a disease and getting sicker from a disease they contract,” she added. “The safest and most effective way to protect children is to vaccinate them on schedule.”