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Can a Vaccine Prevent Herpes Outbreaks? —Commentary

12/15/16 Sheldon R. Morris, MD, MPH, University of California San Diego;

Researchers recently reported a successful test of a new vaccine for the herpes virus. Does this mean we will soon be able to use vaccines to eliminate herpes infections just like we’ve nearly eliminated some other virus infections (for example polio and measles)?

 Not yet, unfortunately.

 What is a herpes infection?

 Infection with the herpes simplex virus causes recurring episodes of small, painful, fluid-filled blisters on the skin, mouth, lips (cold sores), eyes, or genitals (genital herpes). Herpes simplex infection causes many problems across the globe. Experts estimate that over 400 million people worldwide are infected. In addition to the discomfort that genital herpes can cause, genital herpes can also cause life-threatening illness such as encephalitis (brain infection) and other serious infections in newborn babies if the virus is passed to a newborn during the birth process. And having herpes simplex virus infection can increase the risk of acquiring HIV infection.

 Why do we need a herpes vaccine?

 A big problem with the herpes virus is that once people have an infection, the virus stays with them for life. The virus stays dormant in the body and at various times reactivates and causes symptoms. Even when there are no visible blisters and no symptoms, the virus may be present on the genitals and can be spread to sex partners.

One way to help prevent genital herpes from spreading is to use condoms at all times, which can reduce transmission by about 90%. Another  way is to take an antiviral drug, such as acyclovir, valacyclovir, or famciclovir. Although these drugs do not clear herpes virus from the body, they can decrease the number of outbreaks and reduce the length of an outbreak. However, people need to take the antiviral drugs every day, and the drugs do not work for all people. A herpes vaccine ideally could be given in only a few doses (like other vaccines) but provide long-term protection. Researchers have therefore been looking for a vaccine to prevent transmission of herpes simplex virus.

 Is the new herpes vaccine the solution we want?

 Not quite, but the results are encouraging. The researchers recruited people who already had genital herpes infection and gave them three injections of their new vaccine or a placebo (dummy vaccine). Then they watched the people for a year to see

  • How often they got outbreaks of herpes blisters
  • How much herpes virus they were releasing (shedding) based on test swabs taken from their genitals

 The investigators tested different doses of the vaccine. The most successful dose decreased the amount of virus that infected people were shedding by 66%, and decreased the number of new herpes blisters by 65%. This is about the same decrease as when people take antiviral drugs daily. These results are promising, but there is much researchers still don’t know.

  • Because they didn’t directly compare the vaccine with oral antiviral therapy, they can’t say whether the vaccine is more effective than daily antiviral therapy.
  • Because people were studied for only one year, they don’t know whether the vaccine is effective for longer than that.
  • Most importantly, this vaccine is meant to be a treatment for recurrent herpes and they don’t know whether this vaccine could PREVENT getting herpes virus infection.

The results of this study are encouraging. However, it is important to note that this vaccine does not prevent infection with the herpes simplex virus and it only reduces viral shedding and the number of herpes blisters rather than eliminating them, and that is far from ideal. Ideally, researchers would like to develop a vaccine that would be as effective as the vaccine that is used to prevent chickenpox (caused by another type of herpes virus). Clearly, further studies will be needed to further confirm effectiveness and safety for this vaccine before any commercial product will be available.