Even a mild COVID infection can cause permanent damage to men’s sperm concentrations and their ability to swim, according to a new study presented at the 39th annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) on June 26.

According to Professor Rocio Nunez-Calonge, scientific advisor at UR International Group at the Scientific Reproduction Unit, in Spain, even after an average of 100 days following SARS-CoV-2 infection, there appeared to be no improvement in sperm quality and concentration, although new sperm would have been produced in that time.

“There have been previous studies that show semen quality is affected in the short term following a COVID infection but, as far as we are aware, none that have followed men for a longer period of time,” Nunez-Calonge said.

“We assumed that semen quality would improve once new sperm were being generated, but this was not the case. We do not know how long it might take for semen quality to be restored and it may be the case that COVID has caused permanent damage, even in men who suffered only a mild infection,” she added.

For the study, the researchers recruited 45 men attending six reproductive clinics in Spain between February 2020 and October 2022. All had a confirmed diagnosis of mild COVID, and the clinics had data from the analysis of semen samples taken before the men were infected.

Another semen sample was taken between 17 and 516 days after infection. The researchers analysed all the samples taken up to 100 days after infection and then analysed a subset of samples taken more than 100 days later.

They found a statistically significant difference in semen volume (down 20 per cent from 2.5 to 2 millilitres), sperm concentration (down 26.5 per cent from 68 to 50 million per ml of ejaculate), sperm count (down 37.5 per cent from 160 to 100 million per millilitre of semen), total motility that is, being able to move and swim forwards (down 9.1 per cent from 49 per cent to 45 per cent) and numbers of live sperm (down 5 per cent from 80 per cent to 76 per cent).

Half of the men had total sperm counts that were 57 per cent lower after COVID compared to their pre-COVID samples.

While the shape of the sperm was not significantly affected, even after 100 days following COVID infection, the sperm concentration and motility showed no improvement.

“The continuing effect of COVID infection on semen quality in this later period may be caused by permanent damage due to the virus, even in mild infection. We believe clinicians should be aware of the damaging effects of the SARS-CoV-2 virus on male fertility. It is particularly interesting that this decrease in semen quality occurs in patients with mild COVID infection, which means that the virus can affect male fertility without the men showing any clinical symptoms of the disease,” said Prof. Nunez-Calonge.

It is known that the SARS-CoV-2 virus can affect the testicles and sperm, but the mechanism is still unknown. While calling for more research, she said that inflammation and damage to the immune system that is seen in patients with long COVID might be involved.