Herpes Vaccine Won't Offer Complete Protection.
"I think there's great hope that we're going to have a vaccine. One of these days we're going to get some control over this disease. But I don't think we're going to entirely eliminate the epidemic," said Dr. Stanberry, who is the Albert B. Sabin Professor of Pediatrics at the University of Cincinnati.
Based upon current understanding of the immunobiology of genital herpes, the best that can reasonably be hoped for from any of the numerous promising prophylactic vaccines now under development is induction of an immune response that will increase the infection threshold. But, that's a clinically meaningful achievement.
With such a vaccine, a person will require exposure to much more virus to become infected. Most--but not all--cases of symptomatic first-episode genital herpes would be eliminated among vaccinated individuals.
"Based upon some animal data, it would appear that it's theoretically possible to completely prevent the establishment of latent infection, in which case we would see vaccinated people becoming infected, replicating in the periphery, developing no disease, establishing no latency, and therefore giving no risk for subsequent transmission.
"I think that's probably the highest goal we can expect for a herpes vaccine," he added.
With widespread use of such a vaccine, one would anticipate a scenario in which vaccinated individuals run a lesser risk of becoming infected. And if they do become infected, they are less contagious; that is, they shed virus less frequently and in lesser amounts than nonvaccinated individuals. This should result in a spiralling reduction in disease spread.
It's quite possible that a genital herpes vaccine will have very different effects in men and women. Since the female genital tract is lined with mucosal cells, it may be possible to produce immune responses that will protect women from viral acquisition to a much greater extent than men. In men, the goal of immunization is more challenging--protection of abraded keratinized epithelium, the investigator continued.
The immunologic correlate of protection against genital herpes infection is unknown and will remain so until there is a vaccine of proven efficacy. But based upon both animal and human data, it appears local immunity will be key to inducing responses that protect the genital tract against infection.
"The most important element of the immune response is going to be cellular, not humoral," Dr. Stanberry predicted. "Developing circulating, neutralizing antibody is clearly a strategy that's not going to be effective in managing this disease. There's no viremia present in infected individuals."
The genital herpes vaccine development process is going so well that it's not too early to address who should receive a vaccine, once licensed. Dr, Stanberry strongly favors universal immunization over a targeted approach. Herpes simplex virus type 2 seropositivity is already so widespread by adolescence that it's difficult to know who to target.
Besides, a genital herpes vaccine that's effective against both type 1 and type 2 disease might also be effective in controlling nongenital infections, including ocular and oral/labial herpes.
The most important but still unanswered questions from a public health standpoint are whether vaccination against genital herpes can reduce the risks of neonatal herpes infection and HIV transmission. Evidence from animal studies suggests the answer may be yes to both, but more work is needed.
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|Publication:||OB GYN News|
|Date:||Oct 1, 1999|
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