In other words, babies born to HIV-positive mothers who do not receive prenatal transmission-reducing drugs have, on average, a 75 percent to 80 percent chance of being born free of HIV.
"That's a rather surprising statistic, I think, because you think to yourself: If the mother has HIV, won't the newborn almost certainly also have HIV?" Kline said. "In fact, even in an era in which we did nothing at all, only minor numbers of infants actually acquired HIV infection."
According to the Centers for Disease Control and Prevention, the number of children born with HIV decreased dramatically in the 1990s from nearly 1,700 babies per year to fewer than 150 babies per year. Worldwide, however, 330,000 HIV-positive babies were born in 2011, according to the United Nations.
Gay ran virologic tests when the baby was 30 and 31 hours old, which bore results consistent with in utero infection, according to the study, but the study did not mention that those results took several days to process, and Gay did not wait for answers before beginning treatment.
What Was the Treatment?
Doctors usually give newborns of HIV-positive mothers one antiretroviral -- nevirapine -- for the first six weeks of life, at which point they can confirm that the HIV antibodies or HIV DNA and RNA fragments in tests actually belong to the baby, and weren't passively passed from the mother during birth. By the time the baby is 6 weeks old, the mother's antibodies and viruses are expected to be gone from the baby's body, eliminating the chance of a false positive HIV test result. (Kline said false negatives were far more likely.)
But Gay decided that this baby's risk was too great for standard care.
"When we consider starting any medication in any patient, we always consider the risk-benefit ratio," Gay said in a news conference last March. "When the risk is something as serious as HIV disease, then it's worth the benefit that you may get from preventing that disease. Even though you never want to start drugs that may cause toxicities, if the benefit outweighs the risk, you do it."
So instead of a standard dose of nevirapine, Gay administered three antiretroviral drugs -- AZT, 3TC and a double dose of nevirapine – when the baby was 30 hours old, according to Dr. Deborah Persaud, who works at Johns Hopkins Children's Center. Persaud would become Gay's research colleague 18 months later, and has studied the Mississippi baby's case.
Nevirapine was given twice a day, which is the higher dose needed to treat HIV infection rather than prevent it, Persaud said.
Gay said the baby's treatment was "in no way experimental," because the drugs had been used before and are approved by the U.S. Food and Drug Administration. But Persaud said she did not know of any other cases in which a child had been treated this early with this combination of powerful drugs.
Although Gay began administering treatment-size doses, a diagnosis was not yet clear. It wasn't until several days into the therapy that Gay confirmed the baby was HIV-positive with the virologic testing initiated before treatment.
Gay learned -- and outside researchers later confirmed -- that the baby had such high viral loads that it would be "virtually impossible" for it to have had anything other than an HIV infection.
What Are the Risks of These Drugs?
In the short term, these drugs carry the risk of liver inflammation, allergic reactions, and bone marrow suppression, which can predispose the patient to other infections, Kline said.