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Even mild Covid reduces sperm counts – Spanish study

Men recently infected with Covid-19 have decreased sperm counts for more than three months after even mild infections, and the sperm they that do produce is less able to swim, according to new findings presented recently at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Denmark.

Men produce new sperm every two to three months, so the findings are intriguing, said the scientists, because the findings are based on semen analyses taken after 100 days. This suggests Covid does long-term damage to the male reproductive tract.

"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 that Covid has caused permanent damage, even in men who suffered only a mild infection," said lead researcher Rocio Nunez-Calonge, a scientific adviser at the Scientific Reproduction Unit in Madrid, Spain.

The study was based on findings from semen samples produced by men visiting six reproduction treatment centres in Spain between February 2020 and October 2022. Forty-five men participated in the study.

All 45 provided a semen sample before there were sickened with Covid-19 infection classified as mild. Follow-up samples were taken 17 to 516 days after infection; the median time that elapsed between the pre- and post-Covid samples was 238 days.

Semen volume down by 20%

Semen volume decreased 20% between pre-and post-Covid samples (from 2.5 to 2 ml [mL]), and sperm counts fell 37.5%, from 160m to 100m per mL of semen.

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.

Additionally, sperm concentration, the number of live sperm in a sample, decreased 26.5%, from 68m to 50m per mL of ejaculate. The total motility of sperm went down by 9.1%, from 49% to 45%, and numbers of live sperm decreased 5%, from 80% to 76%.

The shape of sperm was not significantly changed.

A subset of men who provided samples more than 100 days after infection confirmed that the decreased quality and quantity of sperm persisted.

“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,” said Nunez-Calonge.

“We believe clinicians should be aware of the damaging effects of SARS-CoV-2 virus on male fertility.”

Inflammatory process possible involved

The exact mechanism for the damage is unknown, but Nunez-Calonge said the inflammation caused by Covid-19 may be at play.

“The inflammatory process can destroy germ cells by infiltrating the white blood cells involved in the immune system, and reduce testosterone levels by affecting the interstitial cells that produce the male hormone,” she said. Her research team will continue to track these 45 men to determine how and if sperm quality changes over time, she added.

Commenting on the work, Carlos Calhaz-Jorge, PhD, of Northern Lisbon Hospital Centre, who was not involved in the research, said it was intriguing but requires more investigation.

“It’s important to note that the semen quality in these patients after a Covid infection is still within the World Health Organisation’s criteria for ‘normal’ semen and sperm,” he said.

“So, it is unclear whether these reductions in semen quality after a Covid infection translate into impaired fertility, and this should be the subject of further research.”

Study details

What is the recovery time for sperm parameters in men who have suffered a mild Covid-19 infection?

R Nunez – Calonge, J A Guijarro, T Rubio, P Alberola, G Fernández, N Santamaria, S Alonso, I Barros

Published in Human Reproduction on 1 June 2023.


Study question
What is the time required in men who have suffered a mild Covid-19 infection, for the seminal parameters to be restored to the pre-Covid values?

Summary answer
The effect of Covid-19 infection on the concentration and sperm motility is clearly confirmed and is maintained over time, at least beyond 100 days.

What is known already
Although several studies have been performed on the effect of SARS-CoV-2 on reproductive health in the short term vs. healthy controls, and the negative effect on sperm parameters has been demonstrated, there is a scarcity of data showing the degree to which the virus affects the semen parameters in one group of patients after coronavirus infection compared to before infection. Moreover, there are no conclusive data regarding the long-term effects of SARS-CoV-2 on semen parameters.

Study design, size, duration
This prospective study was carried out in 6 reproductive centres between February 2020 and October 2022 including 45 male patients with a confirmed diagnosis of mild COVID-19. For each of the semen parameters (volume, sperm count, active and total motility, normal morphology, and vitality) a standardized index was calculated by dividing the value of the parameter from the subsequent semen analysis by that from the semen analysis of the same individual prior to infection.

Participants/materials, setting, methods
The median age of the participants was 31 years, proving the absence of a relationship between age and any of the parameters analysed. The post-Covid test was performed between 17 and 516 days after infection, with a median of 100 days. The time elapsed between both samples was a median of 238 days. The effect of time on the affectation of semen parameters was studied, setting 100 days as the cut-off point.

Main results and the role of chance
There were significant differences in semen parameters before and after Covid-19 in terms of semen volume, sperm concentration, progressive motility, total motility, and vitality which decreased significantly (p < 0,05) after SARS-CoV-2 infection compared to the pre-infection values. Morphology was not significantly affected. The total sperm count is the most clearly affected seminal parameter. Half of the individuals (median) obtained a total count in the second sample less than 57% of the initial one.
Considering the time of spermatogenesis, the subjects were separated into two groups: those who performed the semen analysis in the first 100 days after infection and those who performed it later. No differences in any parameter were found between the two groups with U Mann-Withney test. Using the Wilcoxon test for paired samples, it was demonstrated that the deleterious effect of infection on sperm concentration and motility not only does not improve with time, but it becomes more significant in late sperm analysis, performed more than one hundred days after the infection.

Limitations, reasons for caution
It should be mentioned that impairment of semen parameters may not be due to a direct effect of the SARS-CoV-2 virus. There are likely to be additional factors that contribute to long-term sperm parameters decrease, but whose identity is currently unknown.

Wider implications of the findings
The present study revealed the long-term impacts of SARS-CoV-2 on various parameters of sperm quality even with a mild infection. Further efforts should be made to study the long-time effects of Covid-19 infection on male reproduction.


Human Reproduction article – What is the recovery time for sperm parameters in men who have suffered a mild Covid-19 infection? (Open access)


CIDRAP article – Study: Sperm counts decline even after mild COVID infections (Open access)


See more from MedicalBrief archives:


Unpacking COVID vaccination’s effect on fertility and sexual functioning


Small Chinese study finds COVID-19 in patients’ semen


SA’s fertility rate likely to drop since COVID, says Stats SA








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