Do Men and Women Need Different Versions of the Same Vaccine?

Evidence is building that sex differences affect disease prevention, most recently in the arena of vaccines. Accumulating evidence suggests that men and women may have different needs for and responses to immunizations against the same disease. Researchers recently discovered that a vaccine against genital herpes was up to 73 percent effective, but exclusively in women. The same vaccine gave men no protection against infection. Spotswood Spruance, MD, Professor of Medicine at the University of Utah School of Medicine and lead author of the study, was surprised that "Women had all the benefit."

"Vaccine research is an example of just how broad the implications of sex differences are," noted Sherry Marts, PhD, Scientific Director of the Society for Women's Health Research. "When it comes to infectious disease prevention, we have to understand how men and women differ." At a meeting on sex differences in the immune system, co-sponsored with Harvard Medical School last November, the Society for Women's Health Research examined how men and women in the military react differently to the anthrax vaccine.

While Dr. Spruance's report was the first to announce the finding of a vaccine effective in only one sex, other studies have produced similar, though less dramatic, sex-specific results. Vaccines against anthrax, hepatitis, influenza, and rubella all elicit some degree of sex-specific immune response and cause different side effects in men and women. According to experts, this phenomenon deserves further study in order to successfully develop other much needed vaccines such as one against HIV, a disease in which sex differences are numerous and varied.

Herpes Vaccine Study Details
Dr. Spruance and colleagues conducted two Phase III trials on a vaccine against herpes simplex virus type 2 (HSV-2). Herpes is a sexually transmitted disease (STD) caused by the herpes simplex virus. HSV-2 causes painful genital sores in the 45 million Americans estimated to be infected. The more common form of the virus, HSV-1, causes blisters on the mouth and face.

Researchers followed almost 3,000 individuals in monogamous relationships in which one partner had genital herpes. Study participants randomly received either the herpes vaccine or a placebo ("dummy") vaccine. Approximately three percent of people who received the vaccine developed herpes compared with 11 percent among individuals who were injected with the placebo.

Among one group of women the results were dramatic. Vaccinated women who had never had oral herpes were 73 percent less likely to develop genital herpes symptoms compared with women who received the placebo shot. The vaccine offered no protection to men or women who had been previously infected with the oral version of the herpes virus.

Why the Sex Difference?
Experts can only speculate as to why the vaccine works exclusively in women. Differences in both genital anatomy and immune response probably play a role, according to Dr. Spruance. For women, exposure to the herpes virus usually occurs in the vagina. Here immune cells in vaginal secretions can help fight the virus before infection actually occurs. In men, on the other hand, the virus usually enters through tiny breaks in the skin of the penis where it comes in direct contact with cells it can infect. Thus, perhaps the vaccine helps women by boosting their immune response in the vagina.

Other research suggests that basic differences in male and female immunity are involved. A 2001 report of the Institute of Medicine cites more than ten different sex-specific responses to vaccines. It is well known that women are at least three times more likely than men to develop autoimmune diseases, conditions in which the body attacks itself.

Furthermore, numerous studies have confirmed that women wage a much stronger immune response than men. "There is an actual difference at the cellular level between how a woman and a man mount an immune response," said Marie L. Foegh, MD, Vice President of Female Healthcare at Berlex Laboratories, Inc. "But beyond sex hormones, we still don't know what accounts for that difference."

The Society for Women's Health Research is the nation's only not-for-profit organization whose sole mission is to improve the health of women through research. Founded in 1990, the Society brought to national attention the need for the appropriate inclusion of women in major medical research studies and the resulting need for more information about conditions affecting women. The Society advocates increased funding for research on women's health, encourages the study of sex differences that may affect the prevention, diagnosis and treatment of disease, and promotes the inclusion of women in medical research studies. Dr. Donnica Moore has been a member of the Society since 1990 and is a past member of its Board of Directors.

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Created: 3/18/2002  -  Donnica Moore, M.D.