A baby has been born with Covid-19 antibodies in the United States, weeks after her mother was vaccinated against the disease.

The new born baby's mother received her first dose of the vaccine in late December.

Children's Hospital of Philadelphia paediatrics expert Dustin Flannery told Mike Hosking it's still unknown how much protection the baby has against the virus.

He says with other protections, the maternal antibodies only last in new born babies for a couple of months.

"Vaccine antibodies are often transferred from mother to baby during pregnancy. It's still unclear how long the antibodies stay in the system.

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