The data, which was meta-analysed, says that the average sperm concentration fell from an estimated 101.2m per ml to 49.0m per ml, a stark drop of 51.6%.
The study, published on Thursday in the journal JAMA, recruited 45 healthy male volunteers aged 18 to 50 years scheduled for mRNA COVID-19 vaccination by Pfizer-BioNTech and Moderna.
