New York — Pharmaceutical manufacturer Merck & Co. has begun a small-scale human trial of a new experimental HIV vaccine, the Wall Street Journal reported Thursday.

The vaccine has so far prevented AIDS in laboratory monkeys that were injected with HIV strains that can sicken humans and monkeys, the newspaper quoted sources as saying.

The vaccine did not stop the animals from contracting the HIV virus, but their bodies have been able to control it, at least for now, people familiar with the experiments told the newspaper.

The company, based in Whitehouse Station, N.J., would not discuss details of the laboratory trials, but said it began testing the vaccine in healthy, uninfected volunteers last week. The initial human trials are only to ensure that the vaccine doesn't harm people, not to test whether it works.

Thirteen different AIDS vaccines are currently in clinical trials, and some are farther along than the new Merck vaccine, according to a recent survey of drug companies by Pharmaceutical Research and Manufacturers of America, the industry trade group.

Two being developed by Wyeth-Lederle Vaccines, a division of American Home Products of Madison, N.J., are being tested for safety in people.

Sources familiar with Merck's research told the Journal that its experimental vaccine combines a new vaccine with an older one. It puts parts of HIV's genetic material directly into people to stimulate immune cells called killer T-cells that destroy cells infected by the virus, and it puts HIV genes into a deactivated cold virus to greatly boost the number of killer T-cells that go on the offensive.

Merck officials said they plan to present their findings at a scientific forum in April. They already presented data to a closed-door session with the National Institutes of Health advisory committee on AIDS vaccine and another session with AIDS activists, the newspaper said.

David Baltimore, Nobel-winning scientist who heads the NIH committee, said, "After the presentation, members of the committee were excited." He said he could not give details.

Some experts told the newspaper they worry the vaccine may merely delay onset of AIDS. But even that could be a big advance: A reduction in the virus level might reduce the chance of a person transmitting it to others.

Worldwide, about 35 million people are living with HIV or AIDS.