New paper in Family practicepublished by Oxford University Press, shows that taking hormone replacement therapy for six months after a registered diagnosis of COVID-19 was associated with reduced mortality from the disease.

The new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread. Men and women are equally prone to infections. However, men tend to have more severe infections and have higher hospitalization and mortality rates. A recent survey of gender differences in COVID-19 using data from 38 countries found that male mortality was 1.7 times higher than that of women. Complications of COVID-19 are less likely to occur in young women or women with higher estrogen levels.

Previous studies have also shown that women have a faster and greater immune response to viral infections. Researchers have observed similar data in previous pandemics, including outbreaks of SARS-CoV (Severe Acute Coronary Syndrome Virus) and MERS-CoV (Middle Eastern Coronavirus Syndrome).

The cause of these gender differences is uncertain. Limited recent observational evidence suggests that estrogen may reduce the severity of COVID-19 disease. This study investigated the relationship between hormone replacement therapy or combined oral contraception use and probability of death in women with COVID-19. Researchers have investigated combined oral contraceptives containing estrogen because some recent observational data suggest that women are taking oral contraceptives have a lower risk of COVID-19 infection.

Investigators used a retrospective cohort of medical records from the database of the Oxford-Royal College of Primary Care Research and Supervision of General Practitioners. They identified a group of 1,863,478 women over the age of 18 from 465 general practitioners in England. The cohort registered 5,451 cases of COVID-19. Hormone replacement therapy was associated with a 22% reduction in all-cause mortality from COVID-19.

This suggests that estrogen may contribute to the protective effect against the severity of COVID-19. This may explain why fewer women compared to men were hospitalized, hospitalized in intensive care or died because of COVID-19 during the pandemic.

“This study confirms the theory that estrogen may offer some protection against the severe form of COVID-19,” said Christopher Wilcox, one of the authors of the article. “We hope this study can reassure patients and clinicians that there are no signs of discontinuing hormone replacement therapy because of the pandemic.”