Coronavirus seems to hit men harder but go easy on women. why?

Scientists say women are developing stronger immune responses to the infection. Yet people smoke in far greater numbers in China.

The coronavirus that emerged in China has spread anxiety and fear all over the world. Yet, while the novel virus has largely spared one vulnerable group — kids— it seems to pose a particular threat to middle-aged and older adults, especially men.

The Chinese Center for Disease Control and Prevention conducted the most extensive analysis of coronavirus cases to date this week. Although men and women were infected in roughly equal numbers, researchers found that the mortality rate among men was 2.8 per cent, compared to 1.7 per cent among women.

Men were also disproportionately impacted during outbreaks of SARS and MERS caused by coronaviruses. In Hong Kong in 2003, more women than men were diagnosed with SARS but, according to a study published in the Annals of Internal Medicine, the mortality rate among men was 50 per cent higher.

Approximately 32 per cent of men with Middle East Respiratory Syndrome died, compared to 25.8 per cent of women. During the 1918 influenza outbreak young adult men also died at higher rates than female peers.

In the current outbreak, scientists say, there may be a number of factors working against men, including some biological ones, and some lifestyle rooted ones. Men are the poorer category when it comes to building an immune response to infections.

"This is a trend we've seen with other viral respiratory tract infections — men can have worse results," said Sabra Klein, a scientist at the Johns Hopkins Bloomberg School of Public Health who studies sex differences in viral infections and vaccine responses.

Women also produce stronger immune responses after vaccinations and have enhanced memory immune responses, which protect adults from pathogens they were exposed to as children.

"There's something about the immune system in females that is more exuberant," said Dr. Janine Clayton, director of the Office of Research on Women's Health at the National Institutes of Health.

But there is a high price, she added: women are much more vulnerable to autoimmune diseases, such as rheumatoid arthritis and lupus, where the immune system goes into overdrive and assaults the organs and tissues of the body itself.

Nearly 80 per cent of those with autoimmune diseases are women, Dr. Clayton noted.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3328995/

The reasons women have stronger immune responses aren't entirely clear, and the research is still at an early stage, experts caution.

One theory is that the stronger immune systems of women confer a survival advantage on their children, who imbibe antibodies from the breast milk of mothers that help ward off disease while the immune systems of infants continue to develop.

It may be responsible for a stew of biological factors, including the female sex hormone estrogen, which appears to play a role in immunity, and the fact that women carry two X chromosomes, which contain immune genes. Obviously men carry only one.

Experiments that exposed mice to SARS coronavirus showed males to be more susceptible to infection than females, a difference that increased with age.

With high viral concentrations, the male mice developed SARS, had a poorer immune response and were slower to clear the virus from their bodies. We experienced more lung damage, and died with higher rates, said Dr. Stanley Perlman, a University of Iowa professor of microbiology who was the study's senior author.

When researchers blocked estrogen in the infected females or removed their ovaries, they were more likely to die, but blocking testosterone in male mice made no difference, indicating that estrogen may play a protective role.

"It's an exaggerated model of what happens in humans," Dr. Perlman said. "The differences between men and women are subtle — in mice, it's not so subtle."

In some cultures, health habits that vary by sex can also play a role for differential responses to infections. China has the world's largest smoker population—316 million people— representing almost one-third of the world's smokers, and 40 per cent of the world's tobacco consumption. But Chinese women smoke just over 2 per cent, compared to over half of all men.

Chinese men also have higher rates of type 2 diabetes and high blood pressure compared with women, both of which increase the risk of complications following coronavirus infection. Chronic obstructive pulmonary disease rates among Chinese men are nearly twice as high as between women.

Females are more involved in pursuing health care in the United States than men, and some small studies have found the generalization often extends to Chinese students at U.S. universities. In unpublished reports, Chinese researchers stressed that patients with a delayed diagnosis or with extreme pneumonia when first diagnosed were at the highest risk of dying.

One study of 4,021 patients with the coronavirus emphasized the importance of early detection, particularly in older men. And men have been turning up in hospitals with more advanced disease.

But in areas of China outside Hubei Province, the disease's epicentre and where the majority of those affected are concentrated, the patterns are different: The disease appears to have dramatically lower mortality rates, and men are being infected at much higher rates than women, according to the Chinese C.D.C. analysis.

Men may have a "false sense of security" when it comes to the coronavirus, said Akiko Iwasaki, a professor of immunology at Yale University who studies why some viruses affect women more severely.

Gathering and analyzing data about the new virus by sex is important both for the scientists studying it and for the general public, experts said.

since the outbreak started, public health officials have emphasized how important it is to wash hands well and often to prevent infection. But several studies have found that men— including health-care workers — are less likely than women to wash their hands or use soap. "We make these wide-ranging assumptions that in terms of behaviour, men and women are the same