By Roberta Attanasio
Women and men respond differently to infectious microbes and vaccines – it is said, indeed, that the immune system of women is stronger than the immune system of men. Stronger or weaker, one thing is certain – men and women are not the same in terms of immune response. A few years ago, the journal Lancet Infectious Diseases published “ The Xs and Y of immune responses to viral vaccines” – a comprehensive article that clearly shows how the biological differences between sexes influence the immune response to vaccines, as for example the influenza, yellow fever and hepatitis vaccines. There are not many published studies on the same subject, though. The majority of scientists involved in vaccine research do not consider sex as a variable and, typically, vaccine trials are not designed to take into account the physiological differences that exist between men and women.
If we had to take these differences into account, how would things change when vaccinating human populations? In the New York Times article “Do women need such big flu shots?” Op-Ed contributors Sabra Klein and Phyllis Greenberger provide an example related to one of the influenza vaccines: “Under the current guidelines, men and women are to get equal-sized doses of the H1N1 vaccine. Yet women’s bodies generate a stronger antibody response than men’s do, research shows, so less vaccine may be needed to immunize them. If we could give women a smaller dose, there would be more vaccine to go around. And we might also spare them the mild side effects that vaccines can cause, like pain at the injection site, inflammation and fever. All of these are more common in women than in men.”
In 2010, the World Health Organization published “Sex, Gender and Influenza”, a report that “focuses on the different effects of seasonal epidemics, pandemics and localized outbreaks of influenza on males and females including pregnant women.” The report concludes that “significantly more research is required to gain a more complete understanding of the complex and varied effects of sex and gender on influenza infection and vaccination, and underscores the need to consider their interplay with any infectious disease of global concern.”
However, there are still large gaps in our understanding of how sex differences influence the immune response to vaccines and not enough research is done to fill these gaps. May be, step by step, we’ll get there. Meanwhile, here is one of the steps – a new study found that high levels of testosterone make the immune response to the flu vaccine go south.
The study – “Systems analysis of sex differences reveals an immunosuppressive role for testosterone in the response to influenza vaccination” – was carried out using samples from 53 women and 34 men vaccinated with a seasonal influenza vaccine. Results from the study not only show that women displayed significantly stronger antibody responses to the vaccine – they also show that men with the highest levels of testosterone displayed the lowest antibody responses to the vaccine. Thus, testosterone has immunosuppressive activity.
The authors of the study speculate that lower antibody responses in men might provide an evolutionary advantage. Women produce higher levels of antibodies, but also develop stronger inflammatory responses which, in many instances, lead to more severe disease. Males of many species are more likely to experience trauma than females – thus, their risk of contracting infections because of open wounds is higher. By keeping their responses at a low gear configuration, men can control potentially dangerous inflammation.