Severe cases of Covid-19 might impact the quality of a man’s sperm, thus possibly impacting his fertility, according to a new study published Thursday in the journal Reproduction. “This report provides the first direct evidence to date that COVID-19 infection impairs semen quality and male reproductive potential,” the study said. However, experts not involved in the study were immediately skeptical about the report’s conclusion and urged caution in overgeneralizing the research findings. “I need to raise a strong note of caution in their interpretation of this data. For example, the authors state that their data demonstrates that ‘COVID-19 infection causes significant impairments of male reproductive function’ yet it only actually shows an association,” said Allan Pacey, a professor of andrology at The University of Sheffield in South Yorkshire, United Kingdom, via email. “Being ill from any virus such as flu can temporarily drop your sperm count (sometimes to zero) for a few weeks or months. This makes it difficult to work out how much of the reductions observed in this study were specific to COVID-19 rather than just from being ill,” said Dr. Channa Jayasena, a consultant in reproductive endocrinology and andrology at Imperial College London, in an email. In addition, “it is important to note that there is no evidence of Covid-19 virus in the semen and that there is no evidence that virus can be transmitted via semen,” said Alison Murdoch, who heads Newcastle Fertility Centre at the International Centre for Life, Newcastle University in the UK, via email. Small study of 84 men The study age-matched 105 fertile men without Covid-19 to 84 fertile men diagnosed with the coronavirus and analyzed their semen at 10-day intervals for 60 days. Compared to healthy men without Covid-19, the study found a significant increase in inflammation and oxidative stress in sperm cells belonging to men with Covid-19. Their sperm concentration, mobility and shape were also negatively impacted by the virus. The differences grew with the severity of the sickness, the study found. “These effects on sperm cells are associated with lower sperm quality and reduced fertility potential. Although these effects tended to improve over time, they remained significantly and abnormally higher in the COVID-19 patients, and the magnitude of these changes were also related to disease severity,” said lead researcher Behzad Hajizadeh Maleki, a doctoral student at Justus Liebig University Giessen, in Hesse, Germany, in a statement. There were also much higher levels of ACE2 enzymatic activity in men with Covid, the study found. ACE2, or angiotensin-converting enzyme 2, is the protein that provides the entry point for the novel coronavirus to hook into and infect a wide range of human cells However, it’s not surprising that Covid-19 might impact the male reproductive system because ACE2 receptors, or the “same receptors which the virus uses to gain access to the tissues of the lung, are also found in the testicles,” said Pacey, who is also editor in chief of the journal Human Fertility. An ongoing concern “Since the start of the Covid-19 pandemic, there has been an understandable (but theoretical) concern about whether this coronavirus might have a detrimental impact on the fertility of men who become infected,” Pacey said. After reviewing some 14 studies published on the topic, Pacey said he concluded that “any measurable effect of coronavirus on male fertility was probably only slight and temporary.” The findings of this study, he added, could be due to other factors, such as the use of medications to treat the virus, which the authors also acknowledged in the study. “Therefore, all I see in this dataset are possible differences in the sperm quality between men who are sick with a febrile illness (fever) and those who were well. We already know that a febrile illness can impact on sperm production, regardless of what caused it,” Pacey said. Sheena Lewis, a professor emeritus at Queen’s University Belfast in Ireland, shared similar thoughts via email: “My concerns are that the men with COVID had substantially higher body weight and were on a number of therapeutic treatments. “We know that obesity alone reduces sperm quality. The COVID treatments may also have affected these men’s sperm quality, rather that COVID itself,” Lewis said. “Thus, longer term studies are needed before the testes is considered to be a high-risk organ specific to Covid-19,” Newcastle’s Murdoch said.