Sperm quality declines after mild Covid, according to findings presented during the annual meeting of the European Society of Human Reproduction and Embryology in Copenhagen.

“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,” warned study author Professor Rocio Núñez-Calonge, scientific adviser at the UR International Group at the Scientific Reproduction Unit, Madrid.

Researchers recruited 45 men (median age 31 years) with mild Covid who attended six reproductive clinics in Spain. The clinics analysed semen samples before the men were infected with Covid. Men provided another sample a median of 238 days after the first. Previous studies showed short-term declines in semen quality following Covid. 

“We assumed that semen quality would improve once new sperm were being generated, but this was not the case,” said Núñez-Calonge. 

Men take about 78 days to generate sperm, so the researchers analysed all samples taken up to 100 days after infection. They also evaluated some samples after 100 days. 

After Covid, semen volume had declined by 20 per cent, sperm concentration by 26.5 per cent and sperm count by 37.5 per cent. Total motility fell by 9.1 per cent and numbers of live sperm by 5 per cent between the two samples. 

Half of the men had total sperm counts that were at least 57 per cent lower after Covid compared with their pre-Covid samples. 

“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,” Professor Núñez-Calonge said.