Weaning before a baby is 6 months old is a bad idea for HIV-positive mothers in circumstances where breastfeeding has no safe alternative, researchers reported.

And treatment with anti-retroviral drugs should continue as long as breastfeeding is required, according to Charles van der Horst, MD, of the University of North Carolina, in Chapel Hill, N.C., and colleagues.

The finding comes from 48-week follow-up of a large randomized trial that compared different treatment strategies for six months, and then encouraged weaning without further therapy, van der Horst and colleagues reported online in The Lancet.

The researchers reported in 2010 that treatment of either the mother or infant during the first six months of breastfeeding reduced the risk of HIV transmission, compared with no therapy.

In the current analysis, they looked at what happened when the babies were weaned at 6 months and treatment was stopped.

The bottom line, van der Horst told MedPage Today, is that "weaning puts the baby at risk for ... other infections," such as pneumonia and tuberculosis.

At the same time, he added, it's important to continue therapy as long as the baby is being breastfed in order to continue to prevent HIV transmission.

In the so-called BAN study -- for Breastfeeding, Antiretrovirals, and Nutrition -- 2,369 mother-and-infant pairs in which the mother was HIV-positive got the now-standard perinatal prophylaxis of a single dose of nevirapine (Viramune) and a week of nevirapine and lamivudine (3TC).

All of the mothers had a CD4-positive lymphocyte count of at least 250 cells per cubic millimeter and thus, by then-current standards, did not require anti-retroviral therapy for their own health.

After the first week, they were randomly assigned to no further treatment (the control group), to maternal therapy with a triple-drug regimen, or to infant treatment with nevirapine.

Between 24 and 28 weeks, van der Horst said, the mothers were asked to stop breastfeeding, but were supported with additional care to ensure the infants had adequate nutrition.

Despite that, the researchers found, the rate of serious adverse events in infants was markedly higher during weeks 29 through 48 than during the intervention phase.

Specifically, during the intervention phase, the overall rate of adverse events among the babies was 0.7 per 100 person weeks, which jumped significantly (at P<0.0001) to 1.1 per 100 person weeks after therapy was stopped.

Stopping therapy also increased the risk of HIV transmission, they reported.

The cumulative risk of transmission by 48 weeks was 7% in the control group, which was significantly higher (at P=0.027 and P=0.002, respectively) than the 4% seen in each of the treatment groups.

In contrast, the rates at the end of the intervention period had been 5.7% in the control group, 2.9% in the maternal-treatment group, and 1.7% in the infant-treatment group.

Van der Horst said the data suggest that many mothers did not immediately cease breastfeeding even though they said they had.

He added that the study also found a worrisome trend among the mothers -- nine women died during the study, but only one of them was in the maternal-treatment arm. The differences did not reach statistical significance, he told MedPage Today, but they hint that, even for women with relatively robust immune systems, continued therapy may have a health benefit.

Indeed, largely as a result of the study, Malawi has changed its criteria for HIV treatment eligibility. Now, regardless of CD4 count, HIV-positive mothers are placed on triple-drug therapy for life.

The study is one of several investigating similar questions and arriving at similar answers. Combined with other studies suggesting transmission can be prevented by treatment, the findings have important implications for health policy in the developing world, van der Horst said.

Among other things, the findings suggest the "Malawians were correct" in deciding to opt for lifelong therapy for pregnant women, rather than cutting treatment off until medically required.

Nevertheless, the data are "sobering," commented Louise Kuhn, PhD, of Columbia University's Mailman School of Public Health in New York City, and Hoosen Coovadia, MD, of the University of KwaZulu-Natal in Durban, South Africa.

In an accompanying commentary, they noted that early weaning is accompanied by increases in infant death and illness, as well as by faltering growth.

"Early weaning is neither effective nor safe as an HIV prevention strategy," they concluded.

On the other hand, they added, continued anti-retroviral therapy does prevent transmission, and there are hints that even in women who don't need treatment for their own health the drugs reduce the risk of maternal death.