A mother in the US state of Michigan has been sentenced to seven days in jail after she refused a judge's order to have her son vaccinated.
Rebecca Bredow would not let her nine-year-old be immunised after initially agreeing with the father to do so.
Her ex-husband has now been awarded temporary primary custody in order to get the boy the jab.
Michigan parents are legally allowed to skip or delay their children's vaccinations due to personal beliefs.
But Bredow fell foul of the law because she reneged on agreements with her former spouse dating back to November 2016 to have the boy immunised.
The mother-of-two was sentenced on Wednesday for contempt of court after flouting a court order last week to have her son vaccinated.
She and her ex-husband decided at the time of their child's birth that they would space out and delay jabs for their son.
The couple separated in 2008, according to ABC News, but they shared parental custody and the father still wanted the boy vaccinated.
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Oakland County Court Judge Karen McDonald said that even though Bredow was the child's primary caregiver: "Dad gets a say."
Bredow, from the Detroit suburb of Ferndale, said in court on Wednesday: "I am an educated vaccine-choice mother."
She argued that to immunise her son "goes against my beliefs".
"I would rather sit behind bars standing up for what I believe in, than giving in to something I strongly don't believe in," Bredow added.
Anti-vaccination advocates - whose claims have been widely debunked by the medical community - fear the procedure exposes children to harm, and could be the cause of autism.
Child immunisation rates in Michigan are among the worst in the nation, ranking 43rd among the 50 US states, according to Mlive.
Barbara Loe Fisher, president of the vaccine-sceptic National Vaccine Information Center, told the BBC this is not the first time a parent has been jailed for refusing to vaccinate a child.
The federal government does not legislate child immunisation, only issuing recommendations while leaving requirements to states or local school districts.
If a parent does not comply with a school's vaccination guidelines, the child is not permitted to attend school and the parent can be jailed for the pupil's truancy.
For that reason, many anti-vaccine parents choose to home-school their children, Mrs Fisher told the BBC.