(EDGE) As the global community marks another World AIDS Day, a trio of late-stage trials offers renewed hope that a vaccine against the disease may be on the horizon, NBC reports.

One of the three promising new vaccines, dubbed HVTN 702, is a reworking of a prospective vaccine called RV144 that proved to be 30% effective ten years ago. 

RV144 was impressive - and the only time a potential vaccine showed significant effectiveness - but the partial success of that formulation wasn't deemed sufficiently successful to base a vaccination program around. However, with the advent of PrEP, a fully effective vaccine may no longer be the only goal; a partially effective vaccine - say, one that works half the time - could be sufficient, according to Dr. Anthony Faucher, who has long been on the front lines of research.

NBC reports that Fauchi:

...feels "even more strongly now" that a partially effective vaccine would be worth deploying. He said that is because prevention strategies like pre-exposure prophylaxis (PrEP) and treatment as prevention (TasP) "are being so successfully used, even in the absence of a vaccine, that if one or more of these vaccines look good, have a 50-60 percent efficacy, I think that's going to be the game-changer for turning the epidemic around."

NBC noted that researchers expect to know how effective HVTN 702 will prove to be in about a year.

The other two promising vaccines in development are called Imbokodo and Mosaico. The name of the latter reflects the "mosaic" nature of the vaccines, which the National Institutes of Health explain as incorporating "vaccine components designed to induce immune responses against a wide variety of global HIV strains," according to a report in UK newspaper the Daily Mail.

Reported The Daily Mail:

The second trial, of Imbokodo, began in five southern African nations in 2017. Some 2,600 women have been enrolled in the study....

Mosaico will recruit 3,800 gay men and transgender people for its clinical trials at 57 sites in the US, Latin America and Europe.

A vaccine has been the elusive prize since the epidemic began in the 1980s. At the time, there were predictions of a vaccine in just a few years, but HIV has proven difficult to develop a vaccine against.

As Forbes reported:

HIV has a number of features that make it difficult to vaccinate against. One is that it doesn't naturally stimulate enough of an immune response when it infects you.

.... Secondly, HIV is a bit like Loki or Mystique, coming in many different forms. An immune response against one form may not be effective against other forms. The third is the lack of correlates of protective immunity. These are ways to measure your level of immunity against HIV.... [This] is not there for HIV.

But having three potentially effective vaccines in the works - especially coupled with existing prevention measures, like PrEP - represents a rare spot of genuine optimism in the long fight against HIV/AIDS. In other words, there is reason for measured, cautious hope - but hope all the same