While cautiously optimistic, experts stressed that much remained unclear -- including whether this may have been a freak result.
"The world needs to see this as a proof of concept, but we are not anywhere near implementation" of similar treatment for all newborns at risk, said Harry Moultrie, a paediatric HIV researcher at the University of the Witwatersrand in South Africa, which has a high share of infants born HIV-positive.
"One case does not make an intervention that you can just roll out," said Moultrie, even as he hailed the result "a compelling description of a cure".
Researchers from the Johns Hopkins Children's Center in Baltimore, Maryland, earlier reported they had cured a baby born with HIV.
This was a "functional cure" rather than a full one, as traces of the virus were still present in the child's cells, but at non-dangerous levels.
The baby girl was given a cocktail of three anti-AIDS drugs within 30 hours of being born.
Normally, babies born to HIV-positive women are given a lower, preventative dose of drugs for several weeks, after which full treatment starts upon HIV diagnosis.
In this case, the child remained on antiviral treatment for 18 months. Ten months after treatment was stopped, no HIV was detectable in her blood with standard tests.
"They (the researchers) need to keep a close eye on this child to check that the HIV isn't going to reassert itself further down the line," said Genevieve Edwards of the Terrence Higgins Trust, a UK-based AIDS charity.
She warned the girl may be one among a handful of people whose immune systems don't need drugs to keep the virus from replicating.
Moultrie added it remained to be seen whether the treatment would work on all strains of the virus.
"This was one child and we are not sure of the generalisability or reproducibility of the result," he told AFP.
"If we give the same intervention to 100 children we do not know what proportion of them will give the same result; it may be five percent, it may be 80 percent."
UNAIDS welcomed the development which "gives us great hope that a cure for HIV in children is possible and could bring us one step closer to an AIDS-free generation."
But it cautioned that more study was needed.
"The important thing to concentrate on is to prevent children getting HIV in the first place," said Oxford University AIDS researcher John Frater.
This is best done through screening pregnant women and putting those with HIV on antiviral treatment to prevent transmission.
Frater stressed that parents must not interpret the news as meaning they can take their children off AIDS drugs.
"It is important not to extrapolate from one single case to others. Plenty of children who would stop therapy would rebound."
If confirmed, however, the American research would be a massive breakthrough in the fight against a disease that has claimed some 35 million lives.
"Up until two or three years ago, the general scientific belief was that a cure for HIV was impossible: that we shouldn't research it or invest in it," said Frater.
"Cases like this tell us that a cure for HIV is not impossible... that this is an area of research that we should concentrate on."
WHO statistics show that the bulk, 299,000, of children born with HIV were in sub-Saharan Africa -- about a tenth of them in South Africa in 2011.