At what point can we consider PrEP an HIV vaccine?
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Despite many attempts, an effective vaccine against HIV has remained elusive.
More than a decade ago, however, daily oral PrEP was introduced and has become a successful tool for preventing new HIV infections, with an effectiveness approaching 100% when taken as prescribed.
More recently, an FDA-approved long-acting injectable PrEP that is administered every 2 months has provided another option that does not involve taking a pill every day.
Given PrEP’s effectiveness and the arrival of new medications that can be taken at greater intervals, we asked Aaron E. Glatt, MD, MACP, FIDSA, FSHEA, chairman of the department of medicine and chief of the division of infectious diseases at Mount Sinai South Nassau and professor of medicine at the Icahn School of Medicine at Mount Sinai; Martin S. Hirsch, MD, professor of medicine at Harvard Medical School and a physician at Massachusetts General Hospital; and David M. Margolis, MD, director of the University of North Carolina at Chapel Hill HIV Cure Center, if PrEP should ever be considered a vaccine for HIV.
Glatt:
I don’t think you can “consider it a vaccine,” but I do think it is something that will continue to be very useful.
PrEP is something that has the potential to save a lot of lives, but it’s still taking a medication on a regular basis that can easily be forgotten or missed, as opposed to a vaccine, which is hopefully a one-time deal or maybe a once-a-year deal — whatever needs to be done — and then you’re covered, depending on how good that vaccine is.
Obviously, right now, we have no vaccine, so PrEP is a very good option for the appropriate patient. However, any time you have to take a pill like PrEP — or even a bimonthly injection — you have to rely upon a person to remember to take it take it properly. We can’t be surprised that compliance will never be perfect. Because of compliance concerns, plus the need for repetitive use, there is more risk for potential drug toxicity, more potential side effects, more potential risk, and potential costs. Thus, a safe vaccine is far superior to giving a drug every time you’re in a situation to prevent something.
Maybe — with the newer technology that we’ve developed for other vaccines — maybe there are applications in the HIV world, but it’s not known yet.
Hirsch:
It really depends on whether you’re talking literally or figuratively. PrEP will never be a vaccine if you’re talking about the literal definition of a vaccine because that is a preparation designed to induce immunity to a given virus or other micro-organism.
PrEP involves the use of antiviral drugs. Instead of asking if we can call it a vaccine, I think a better question would be, “Is PrEP going to be available to prevent HIV before an HIV vaccine?” The answer to that is clearly “yes,” because it’s already available, and it’s an effective preventative.
Vaccines against HIV, unfortunately, have proven highly elusive, however, since HIV’s discovery in 1984. Many people thought we’d have a vaccine very shortly. Now, we’re almost 40 years later and we don’t have a vaccine and every major HIV vaccine trial has been negative — including the most recent Mosaico trial.
Unfortunately, a lot of good ideas have been proposed but when put to trial in major vaccine studies throughout the world, they’ve all failed. We still need to continue to try to develop an effective HIV vaccine but we’re not going to have one anytime soon. In contrast, we already have several PrEP studies that have shown that either oral or intramuscular PrEP can safely and relatively reliably prevent HIV infection.
The problem is that PrEP has not been used nearly as widely as it could be. People at highest risk for infection should be taking PrEP much more than they are, whether it’s oral or intramuscular. We must do a much better job of trying to get those at greatest risk to take it, and that’s not an easy task.
Margolis:
PrEP is as effective as an effective vaccine — if not more effective — but you have to take it over and over again, unlike a vaccine. On the other hand, however, there is no effective vaccine yet — or maybe ever.
If everyone who needed protection could access and take PrEP reliably for the rest of their lives, the HIV pandemic would end in 60 years and we would not need a vaccine anymore. On the other hand, though, we have had penicillin for almost 100 years and we still have syphilis.
So, the answer is that we need the best of everything because no one thing will solve the problem.
A cure would be good to have as well, but better tools and better deployment of all the tools are what is needed.
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