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
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.
For more information on vaccines, click here.
Created: 3/18/2002  - Donnica Moore, M.D.