Where flu vaccines for men are concerned, with virility comes virulence, according to a new report released by Stanford.
The report states that men with high levels of testosterone circulating in their blood get less benefit from influenza vaccines, according to the report published Dec. 23 in "Proceedings of the National Academy of Sciences."
The report comes at a time when H1N1, also known as swine flu, is sweeping through the United States. Last week, a 41-year-old woman died of the flu strain in Santa Clara County, and a 48-year-old woman with underlying health issues died later in the week. There have been two flu deaths reported in Marin County this week and two more suspected flu deaths in Santa Clara County.
A 2009 outbreak of H1N1 infected between 43 million and 89 million people worldwide and killed between 8,870 and 18,300 during the same year. But that outbreak was dwarfed by a pandemic of swine flu nearly 100 years ago, according to the Centers for Disease Control.
The "Spanish flu" of 1918 killed as many as 50 million people worldwide and infected about 500 million people, about a third of the world's population at the time, the agency stated.
Men with low amounts of testosterone and women get a strong antibody response from a flu shot, but the hormone doesn't appear to interfere with the body's actual immune response, said Mark Davis professor of microbiology and immunology and director of Stanford'sÂ Institute for Immunity, Transplantation and Infection. Instead, it appears that testosterone may interact with certain genes that dampen the body's response to the vaccine, the report states.
Scientists noted years ago that women have a higher immune response to the vaccinations from the flu, measles, mumps and yellow fever, the report states.
"This is the first study to show an explicit correlation between testosterone levels, gene expression and immune responsiveness in humans," said Davis, who is also the Burt and Marion Avery Family Professor of Immunology. "It could be food for thought to all the testosterone-supplement takers out there."
Men are also more susceptible to viral, bacterial, parasitic and fungal infections than women are, according to the study.
The CDC states that flu-related illnesses kill between 3,000 and 49,000 Americans each year. A separate team at Stanford is trying to reduce that number by developing a universal vaccine to influenza.
Flu strains vary from year to year and today's flu vaccines must target specific strains that health officials believe will be particularly deadly or easily spread, a report from the Stanford School of Medicine states. The officials must make "educated guesses" as to which flu to defend against.
The Stanford team wants to use new understanding of the architecture of flu viruses to create a vaccine that works against a broader range of flu strains and can be manufactured more quickly than current vaccines.
Flu viruses are covered with proteins called hemagglutinins, which resemble the head and stem of mushrooms, the report states. Today's vaccines contain inactivated viruses that identify the "head" of the hemaggluttinins to the immune system and teach it to attack the strain of flu with that hemaggluttinin. The immune system then quickly eradicates the flu strain before it makes its host sick, according to the report.
But the "head" of the mushroom varies from year to year and the "stem" remains relatively constantly. Stanford researchers aim to develop a vaccine that identifies flu viruses based on the hemaggluttinin stem rather than its head, which would theoretically make the vaccine more protective against different strains of flu and could even offer universal protection, according to the report.
"This is an important project for world health," said senior author James Swartz said, noting that the vaccine must not only be broadly effective against different strains of flu but cheap to produce so that it can be widely distributed.
"These are big challenges but we are committed to the effort."
Swartz is the James H. Clark Professor in the School of Engineering and professor of chemical engineering and of bioengineering. The lead author was postdoctoral scholar Yuan Lu.