LOS ANGELES, CA (Catholic Online) - Ironically, the test of a combination of two vaccines followed several big failures. Adding to the general surprise was the fact that Merck's vaccine may have actually increased the risk of infection among men who were both uncircumcised and had prior exposure to the virus used in the vaccine.

"It had an extremely chilling effect on the whole field," Colonel Nelson Michael says, the director of the U.S. Military HIV Research Program.

The Thai study tested Sanofi's ALVAC, a weakened canary pox virus used to sneak three HIV genes into the body, and AIDSVAX, that carried an HIV surface protein.

Both vaccines had very poor showings in individual trials to the point where 22 scientists wrote an editorial in the journal "Science" denouncing it as a waste of money.

And then researchers were pleasantly surprised when the results of the study published in 2009 showed the vaccine combination cut HIV infections by 31.2 percent. The impact upon researchers was huge.

It had taken several years to dispel the series of failed attempts, punctuated by a 2007 trial in which a Merck vaccine appeared to make people more vulnerable to infection, not less - that previously cast a shadow over AIDS vaccine research.

The 2009 clinical trial in Thailand was the very first to show it was possible to prevent HIV infection in humans. Discoveries afterwards have led to even more powerful vaccines using HIV-fighting antibodies.

As many as 34 million people are infected with HIV worldwide and with 2.7 million new infections in 2010 alone; experts say a vaccine is still the best hope for conquering AIDS.

Unlike other viruses, HIV is a moving target, constantly spitting out slightly different versions of itself, with different strains affecting different populations around the world.

New infections have fallen by 21 percent since the height of the pandemic in 1997.

Teams have been working on a vaccine for nearly three decades, but it wasn't until RV144, the 2009 clinical trial involving more than 16,000 adults in Thailand, that researchers achieved any hint of success.

© 2012, Catholic Online. Distributed by NEWS CONSORTIUM.