In most high-income countries, mother-to-child transmission of HIV has fallen to below two per cent, but in poorer regions the virus remains "particularly aggressive", according to a report by the WHO, Unaids and Unicef.
Undiagnosed and untreated
The report found that only 11 per cent of HIV-positive pregnant women in low- and middle-income countries are given drugs to prevent passing the immunity-destroying disease to their children during childbirth, while many children born with the disease are undiagnosed and therefore go untreated.
Treatment access problems were found to be most acute in sub-Saharan Africa, home to 25 million people with Aids and 85 per cent of all HIV-infected pregnant women.
Children in the region account for 14 per cent of those who need treatment, but make up only six per cent of those who are receiving it.
The WHO recommends that children with HIV and those born to HIV-infected mothers are given the antibiotic co-trimoxazole, but the report found that only four per cent of the 780,000 children who needed HIV treatment in 2006 were given the drug.
"A greater effort should be made to follow up HIV-exposed children and to determine the HIV status of all children born to mothers living with HIV/Aids so that appropriate care and support can be provided," the report said.
The UN agencies said more investment was needed in tests that would quickly determine whether children have HIV, and in fixed-doseage drugs that could boost the survival rates of infected young people.
They also called for greater screening for tuberculosis, which can be lethal to those with HIV.