The potentially groundbreaking case could now lead to a cure for children with HIV being created, experts say.
The girl, who is now aged two and a half, has been off medication for a year and has no signs of the infection in her blood, it was announced last night.
Doctors plan to carry out more testing to see if the treatment would have the same effect on other children.
The child, who lives in Mississippi, in the United States, tested positive for HIV – with which her mother was diagnosed shortly before giving birth – after she was born.
Doctors started her on standard drug therapy just 30 hours after she was born and say they believe this was crucial in apparently curing her of the infection.
Her case is the first account of a baby achieving a so-called functional cure, a rare event in which a person achieves remission without the need for drugs, and standard blood tests show no signs that the virus is making copies of itself.
Virologist Dr Deborah Persaud, of Baltimore’s Johns Hopkins Children’s Centre, who led a study into the case, said: “What we have identified is what we think is the first case of a functional cure in a neonatal child.
“This is a proof of concept that HIV can be potentially curable in infants,” she told a major health conference on infections in Atlanta, Georgia, last night.
The expert said the case could change the way high-risk babies were treated and possibly lead to a cure for children with HIV, the virus that causes Aids.
The little girl, who has not been named, was treated with of a cocktail of drugs that are already used to treat HIV infection in infants at the University of Mississippi Medical Centre in Jackson.
They found that after starting treatment, the baby’s immune system responded very well to the medication and tests showed levels of the virus were diminishing until it was undetectable 29 days after birth. Treatment continued for almost a year.
Dr Rowena Johnston, director of research for the Foundation for Aids Research, which helped to fund the study into the baby girl’s case, said the fact that the cure was achieved by antiretroviral therapy offered fresh hope that other babies with HIV could be cured.
She said: “It’s imperative that we learn more about a newborn’s immune system, how it differs from an adult’s and what factors made it possible for the child to be cured.”
In 2007, Timothy Ray Brown of San Francisco became the first person in the world believed to have recovered from HIV.
His infection was eradicated through an elaborate treatment for leukaemia that involved the destruction of his immune system and a stem cell transplant from a donor with a rare genetic mutation that resists HIV infection.
In contrast, the case of the Mississippi baby involved widely available drugs, at a considerably smaller cost.
HIV expert Dr Anthony Fauci of the National Institutes of Health: “You could call this about as close to a cure, if not a cure, that we’ve seen.
“This case opens up a lot of doors to research if other children can be helped. It makes perfect sense what happened.”
But he warned that there was not yet a guarantee the child would remain healthy.
About 300,000 children were born with HIV last year, mostly in poor countries where only about 60 per cent of infected pregnant women get treatment that can keep them from passing the virus to their babies.