MIAMI — A South Florida baby was born with COVID-19 antibodies just weeks after her mother was vaccinated against the disease. Doctors believe the baby is among the first with some protection thanks to the vaccine.

The baby’s mother is a front-line health care worker who got her first dose of the Moderna vaccine in late December. Three weeks later, she delivered a healthy baby girl.

During a routine testing of the blood that comes from the child’s umbilical cord, Boca Raton pediatricians Dr. Chad Rudnick and Dr. Paul Gilbert had the sample tested for COVID-19 antibodies, too.

The doctors had a hypothesis: With other vaccines, like the flu shot, if a mother is vaccinated within a certain time frame, her child will be born with some antibodies. Would the COVID-19 vaccine offer the same?

Their hunch was right. The family was ecstatic.

“Her first question was, ‘What does this mean in terms of protection?’ ” Gilbert said.

The doctors couldn’t give her a definite answer. They knew the baby had some protection but they didn’t know how long the antibodies would last or if they were enough to give the child full protection against the virus.

Data on this is still lacking. There are also no COVID-19 vaccines authorized in the United States yet for kids younger than 16.

What they did know is that the baby being born with some protection was a sign that the world “was turning a corner on this virus,” Rudnick said. Gilbert said they also knew the little girl was probably “one of the first in the world” to be born with antibodies from the vaccine. For now, the doctors are keeping the mother’s identification and other information private.

The news is encouraging, said Dr. Christopher Golden, the medical director at Johns Hopkins Hospital newborn nursery in Baltimore. But he cautions expecting parents not to let their guard down yet, even if they were recently vaccinated.

“There should not be an assumption that babies who have antibodies are covered or protected,” he said.

Golden said there are still too many unknowns: Will the antibodies be effective in protecting the baby against COVID-19? How much of the COVID-19 antibodies does a mother pass on to her child? How long will the antibodies last?

He used the whooping cough vaccine as an example. Mothers who received the vaccine during their childhood carry those antibodies and can pass them on to their babies, which helps protect them initially. But then at around 2 months of age, babies need to get their own vaccinations so they can start building their immune system, he said.

Rudnick and Gilbert, the two doctors who work at Boca VIPediatrics, agree that there is still a lot to learn. The doctors wrote about their findings recently in a “preprint” article on medRxiv. While their medical research is new, it has not yet been peer-reviewed and will require additional study. The two say their finding will be published in BMC Pediatrics in coming weeks.

Other studies have shown that pregnant women who recover from a COVID-19 infection can transfer some antibodies to their newborns, but the amount is lower than what was expected.

Rudnick and Gilbert hope their finding will be treated like a “call to action” and will push researchers to look into how much antibodies newborns can receive from a recently vaccinated mother and how long the protection will last.

As for the mother and her baby, the pair are doing well. The mom has also received her second dose of the vaccine.