A Michigan woman will spend seven days in jail for refusing to vaccinate her son.
Rebecca Bredow was sentenced after ignoring a judge's order to let the 9-year-old boy be immunised.
Her ex-husband, the boy's father, has been awarded temporary custody in order to get his son vaccinated.
Bredow told a judge in the Oakland County Court that it was against her beliefs to immunise her children, The Sun has reported.
"I would rather sit behind bars standing up for what I believe in, than giving in to something I strongly don't believe in," she said.
In Michigan, parents have the right to opt out of immunisation for children for non-medical reasons, but Bredow had reneged on an agreement made with the child's father, Jason Horne, in November 2016 to have their two children immunised.
Judge Karen McDonald said the boy had two parents and "Dad gets a say."
The ruling has sparked an intense debate on social media since the case made headlines in the US.