More than 890,000 people have lost their lives due to the coronavirus, but there are two groups of people for whom the virus is most deadly.
Men and the elderly.
Now, a group of Italian and American scientists suspect they know why.
As part of their study, led by the University of Washington, the researchers analysed samples of viral genetic material taken from 430 COVID-19 patients, as well as 54 people without the disease.
After comparing antiviral and immune responses in the samples – taking into account the time a patient became infected, the amount of virus present, age and sex – they discovered men and older people had weaker immune responses.
In those two groups, researchers found that immune cell responses did not activate until three days after the patient started feeling sick.
They also found that immune cell composition and function fluctuated with viral loads in a way that suggested a dysfunctional antiviral response.
A global trend
Since the coronavirus pandemic began, elderly people and men have suffered higher mortality rates around the world.
This trend was seen as early as February, where one study in China found a fatality rate of 2.8 per cent in men compared with 1.7 per cent in women.
Weeks later in France, figures from the Public Health Institute showed that from March 1 to March 22, males accounted for 57 per cent of COVID-19 deaths, with the average age being 81.
A similar pattern has since emerged in Germany, Iran, South Korea and the United Kingdom.
Australian data, however, bucks this trend.
Females aged 70 and older make up the majority of Australian deaths, government data shows.
“Collectively, our data demonstrate that host responses to SARS-CoV-2 are dependent on viral load and infection time with observed differences due to age and sex that may contribute to disease severity,” the study’s authors wrote.
“Differences in immune responses in males and females are due to a variety of factors, including the effects of sex hormones and the X-linked nature of many immune genes.”
Generally, females are more resistant to infections than males, the scientists said.
This is because females – regardless of age – have more B cells, which help the immune system fight infection by producing antibodies.