The number of young children in the US who are not being vaccinated has continued to rise, along with vaccine exemption rates, according to two reports published by the US Centers for Disease Control and Prevention.

One of the reports released last week says that the number of children who aren’t being vaccinated by the age of 24-months has been gradually increasing.

The second CDC report said that in this past school year was the third consecutive year that saw a “slight increase” in the overall proportion of kids with an exemption.

USA Today reports: Uninsured and Medicaid-insured children were less likely to be vaccinated, according to the 2017 survey. The survey used data from the 2017 National Immunization Survey-Child and focused on children ages 19- to 35-months-old.

Since 2001, the percentage of unvaccinated babies and toddlers quadrupled from 0.3 percent to 1.3 percent in 2015.

Health officials warn that avoiding vaccines could trigger disease outbreaks. For example, measles was believed to be eliminated in 2000, but the CDC notes that outbreaks continue to persist each year — which could be tied to children not receiving the measles vaccine.

Childhood vaccines are controversial, as even celebrity tattoo artist Kat Von D said she plans to raise a “natural” child without vaccinations. However, the medical community insist that vaccines tremendously help protect children against serious diseases. The CDC notes that current vaccine recommendations are backed by extensive research.