A small Chinese study has found there could be a greater chance of catching COVID-19 without even realising it if you're young and a woman.
The virus, which has become one of the leading causes of death in the world since emerging in January, can be spread by people without symptoms.
It's not clear how many people who contract the virus don't show symptoms - estimates range from 2.2 percent (the proportion of confirmed asymptomatic cases in New Zealand) up to 80 percent (a new study which looked at passengers on a cruise ship struck with the disease in March).
Early in the pandemic, Chinese researchers at Zhongnan Hospital in Wuhan began testing patients and close contacts, even if they weren't showing signs of being sick.
They found 42 percent of those who tested positive for COVID-19 had no symptoms. Of those who were asymptomatic, two-thirds were women. Their average age was 37, compared to 56 for those showing symptoms.
The asymptomatic people, whilst still able to spread the disease, were contagious for about eight days, compared to 19 amongst those showing symptoms.
Testing also showed less damage to their immune systems.
"Although patients who were asymptomatic experienced less harm to themselves, they may have been unaware of their disease and therefore not isolated themselves or sought treatment, or they may have been overlooked by health care workers and thus unknowingly transmitted the virus to others," the researchers wrote in journal JAMA Network Open.
"Fortunately, patients with asymptomatic SARS-CoV-2 infection have a shorter duration of viral shedding... and lower risk of a recurring positive test result of SARS-CoV-2 from nasopharyngeal swabs, which can provide a reference for improving the prevention and control strategies for patients who are asymptomatic."
It's still not clear if contracting the disease without showing any symptoms will generate enough antibodies against it to prevent subsequent infections. Other coronaviruses can mutate so rapidly they can be contracted over and over again, as anyone who's had the common cold can attest to.
The evidence so far is SARS-CoV-2 is only mutating slowly, but it's still early days in the pandemic so no one's really sure yet.
