Much more must be done to prevent mother-to-baby HIV transmission, according to new World Health Organization (WHO) guidelines issued Tuesday at the 18th International AIDS Conference in Vienna.

Less than half of HIV-positive expectant mothers receive antiretrovirals (ARVs) to prevent mother-to-child infections, WHO said. More than 400,000 infants acquire HIV each year either in the womb, during labor or breast-feeding. Few children with HIV under one year old receive ARVs, even though if left untreated one-third will die before age one, and half will die by age two.

WHO strongly recommends that HIV virological testing be used to screen infants between four and six weeks of age, with immediate ARVs for infected infants. Virological testing is an improvement upon traditional antibody tests, which cannot distinguish for up to 18 months whether antibodies are the mother's or the baby's. WHO recommends the use of virological assays for infants up to 18 months old.

If the mother or child is on ARVs, it is safe for the mother to breast-feed, WHO says. The small transmission risk is more than offset by the nutritional benefits of breast-feeding in developing nations, said Dr. Gottfried Hirnschall, WHO's director of HIV/AIDS.

Earlier testing and treatment of infants by 12 weeks quadruples their chances of reaching age two, said Jimmy Kolker, chief of HIV/AIDS for UNICEF. With proper treatment from the start, the prognosis for infants is excellent, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.