Women are more than twice as likely as men to have long-term COVID-19, according to the largest study of the disease to date, which found that a history of autoimmune disease or depression also increased the likelihood of developing symptoms.

The study by genetic testing company 23andMe surveyed more than 100,000 people infected with Covid-19, and about a quarter of them reported experiencing prolonged Covid – symptoms such as breathing problems, fatigue and brain fog lasting more than 12 weeks. About 7,000 of them have been formally diagnosed.

Even after the worst of Covid-19 has passed, Long Covid has the potential to become a new public health crisis, keeping employees out of work and increasing the burden on an overstretched healthcare system.

The researchers found that women who contracted Covid-19 suffered disproportionately from chronic Covid-19, despite other studies showing that men were more likely to be infected and more likely to die from the disease. About half of women with long-term Covid have symptoms lasting six months or more.

The higher rates in women may be due to hormonal differences, write 23andMe associate scientists Catherine Weldon and genetic epidemiologist Stella Aslibekyan.

“Scientists know that similar differences exist for other types of conditions. For example, women are more likely than men to develop autoimmune diseases such as lupus or multiple sclerosis,” they wrote.

They add that women typically have two copies of the X chromosome, with the highest number of immune-related genes, meaning that different immune responses are more pronounced in women.

The study’s findings may not be as reliable as other studies because participants reported their own conditions — supporting smaller scientific studies that found women were more likely than men to develop long-term Covid, including earlier this month A study published at the time in the Journal of the Journal of Women’s Health and the United Kingdom focused on discharged patients.

The 23andMe study also showed that about one-third of people who have been chronically infected with the new coronavirus have a history of autoimmune disease, and more than half have a history of depression, anxiety, or cardiometabolic diseases such as heart disease or diabetes. Patients admitted to hospital with Covid-19 are 10 times more likely to develop Covid.

The study found that about a quarter of women with long-term Covid had disrupted menstrual cycles a year after infection.

Estimates of how many people may have long-term Covid vary, but a well-known Penn State study suggests that more than 100 million patients worldwide may have the disease. In the UK, more than a million Britons have reported symptoms at least four weeks after contracting Covid-19, an official survey found.