Plans for a large-scale human trial of a prospecting HIV vaccine in the United States were abandoned on Thursday because a leading federal official said scientists acknowledged the fact that they did not have enough information about the interactions between HIV vaccines and the immune system.

The decision is a major obstacle in the way of the efforts to develop an HIV vaccine, which began 24 years ago, when government health officials guaranteed a marketed vaccine by 1987. In addition to this, health officials have strongly affirmed that such a vaccine would be their best method to bring the AIDS pandemic under control.

Numerous other HIV vaccines are in different stages of investigation all around the world. However, there had been grand prospects for the U.S. government’s trial because the potential vaccine was among a ground-breaking category that intended to stimulate the immune system in a different way.

The official who suspended the government trial, Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said that it was becoming evident that more fundamental examinations and animal testing would be needed before a HIV vaccine was ever marketed. Specialists say that developing a vaccine against HIV is one of the most complicated scientific endeavors in history because of the unexplained nature of the virus.

The trial of the vaccine had been set to comprise 2,400 men in the United States in a study named PAVE 100, according to the Associated Press. Nonetheless, the agency said that it believed that the vaccine did not justify a trial of these proportions. Instead, NIAID said it would coordinate a smaller, more concentrated clinical trial with the purpose to find out whether the product had a remarkable effect on the quantity of virus in an individual’s blood. If a significant effect is observed, then additional research or an enlargement of the study could be carried out.