Spanish researchers announced Tuesday they have developed an AIDS vaccine which cuts the viral load by a significant amount in most patients although they cautioned it is still not enough as a treatment.

Twenty-four AIDS patients took part in a clinical trial carried out by doctors at Barcelona's Hospital Clinic and after 24 weeks the majority had shown a "significant" decrease in their viral load, the hospital said.

"This decrease was very significant is some of them but in no case did the virus become undetectable," a hospital statement said.

"However this is a very important improvement with respect to previous initiatives where with a similar vaccine there was a modest response in 30 percent of the treated patients. No therapeutic vaccine has achieved up to now the same level of response as in this study."

The vaccine was personalized for each patient as it was made from their own dendritic cells, a special type of cell that is a key regulator of the .

It was administered in three doses with an interval of two weeks between each one.

The researchers hope to develop a therapeutic vaccine to treat AIDS which will reduce the need for antiretroviral drug treatments which are expensive as they must be administered daily.

The results of the clinical trial were first published in the Journal of .

A new clinical trial is underway to test the vaccine in conjunction with antiretroviral drugs to allow an improvement in the results.

An estimated 33.3 million people worldwide have the that causes AIDS, according to the the United Nations agency UNAIDS.

Since the beginning of the epidemic in the 1980s, more than 60 million people have been infected with HIV and nearly 30 million have died of HIV-related causes.