When it comes to the deployment and use of an HIV vaccine, researchers say even a partially effective vaccine, although not perfect, still could prevent millions of infections each year.

There are no AIDS vaccines in use, but many are in the development pipeline or clinical trials. The problem is the vaccines are turning out to be less effective than hoped.

To get a handle on what the future might hold, scientists at Oregon State University developed a mathematical model of HIV progression, transmission and intervention, tailored to 127 countries around the world.

According to the model, using current interventions, the world might expect to see about 49 million new cases of HIV in the next 20 years.

But the study concluded that 25 million of those infections might be prevented if ambitious targets for diagnosis, treatment and viral suppression set by the United Nations are met.  

And that’s where an HIV vaccine comes in.

Jan Medlock, the study’s lead author, said adding a vaccine to the mix — even one that is only 50 percent effective — by 2020 could prevent another 6.3 million new infections, potentially reversing the HIV pandemic.

“Partial efficacy is still better than zero efficacy, and it really becomes (a matter) of thinking about the cost and trade-off,” she said. “Are you taking away money from treatment or some other health program to buy these vaccines?  If not, then they’re probably worth doing, even at very low efficacy.”

Medlock’s model — reported in the Proceedings of the National Academy of Sciences — input clinical data from a vaccine that’s now in large-scale trials in South Africa.  

Until it was modified for the phase-three trial in the hopes of boosting its effectiveness, the vaccine candidate showed about a 60 percent efficacy in preventing infection for the first year. The effectiveness dropped to 31 percent 3½ years later.

Even without an improvement in current levels of HIV detection and treatment globally, a vaccine that’s only 50 percent effective has the potential to avert 17 million new cases during the next two decades, Medlock said.

Medlock added an even less effective vaccine could make a sizeable dent to slow the pandemic.

“Twenty percent efficacy at the global population scale is still going to prevent several million infections,” she said.

Medlock said many countries will inevitably fall short of the U.N.’s ambitious goals to contain the HIV pandemic.  

That’s why researchers believe the firepower of imperfect HIV vaccines should be brought to bear in the fight against the AIDS virus.
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