If the attacks come frequently, acyclovir can safely be taken daily to prevent them. Because these attacks are self-limited, cause little disability, do not lead to death or serious complications, and are easily treated or prevented, I call them annoying, but not serious. There are three situations in which herpes infections can be very serious or life-threatening. First, herpes outbreaks in people who are severely immune deficient from HIV infection or cancer chemotherapy can be larger, more painful, and last much longer. Acyclovir and related drugs often are not effective in such cases.
Herpes can also be very serious when the cornea, or surface of the eye, is infected.
Although treatable, the infection can cause whitening of the cornea, which can lead to blindness. Newborn infants can become infected with the herpes virus during a vaginal birth if the mother is shedding virus in the vagina at the time of delivery. Herpes infection in the newborn can be devastating, since newborns do not have an adequate immune system to fight the infection. It can lead to death or permanent disability. It is understandably a frightening prospect for a mother who has herpes, and until recent years it was common for obstetricians to deliver all such infected women by cesarean section.