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Sperm Parameters Before and After COVID-19 mRNA Vaccination

Our take —

Because mRNA vaccines do not contain any live virus, it is very unlikely that the vaccine would affect sperm count. This prospective study, which included 45 cisgender men ages 18 to 50 years in Miami, FL, (enrolled December 17, 2020 and January 12, 2021), quantified sperm parameters before and after mRNA vaccination (Pfizer or Moderna). Although the study included a relatively small number of participants, the researchers did not find any evidence that COVID-19 vaccination negatively impacted sperm volume, concentration, count, or motility.

Study design

Prospective Cohort

Study population and setting

This was a single-center prospective cohort study in Miami, FL, USA that evaluated sperm parameters in 45 men aged 18-50 years before and after mRNA vaccine administration. Participants were enrolled between December 17, 2020 and January 12, 2021. The study excluded individuals with underlying fertility issues, COVID-19 symptoms or positive COVID-19 test results within the last 90 days. Men provided semen samples before their first vaccine dose and around 70 days after their second vaccine dose. Men were requested to remain abstinent for 2-7 days prior to providing semen samples. Semen analysis, performed by trained andrologists, quantified semen volume, sperm concentration, sperm motility, and total motile sperm count. Oligospermia was defined as a sperm concentration <15 million/mL.

Summary of Main Findings

Of the 45 participants (median age 28 years), there was a nearly even split between receipt of BioNTech-Pfizer (BNT162b2: 47%) and Moderna (mRNA-1273: 53%) vaccines. At baseline, samples were obtained after a median abstinence of 2.8 days (IQR: 2-3) and at follow-up, which occurred a median of 75 days (IQR: 70-86) after the baseline sample, median abstinence was 3 days (IQR: 3-4). Between the two samples, median sperm volume (2.2 mL vs. 2.7 mL), sperm concentration (26 million/mL vs. 30 million/mL), sperm motility (58% vs. 65%), and total motile sperm count (36 million vs. 44 million) all increased. Of 8 men who were oligospermic at baseline, 7 had increased sperm concentration into normal range and no new men had new oligospermia. The majority of men (73%) had an increase in total motile sperm count between the two visits, but it is unclear whether differences in duration of abstinence prior to sampling influenced these results.

Study Strengths

Semen samples were collected before and after (median 75 days) mRNA vaccine administration. There were no noted losses to follow-up.


All analyses were unadjusted and did not account for duration of ejaculatory abstinence prior to sampling, which may influence sperm parameters. Given that sperm volume is positively associated with duration of abstinence, the slightly longer median length of abstinence prior to the second sample may have contributed to the increase in sperm volume. The study only included young and healthy men, so it is not clear whether the results would be generalizable to older men or men with other comorbidities. The study did not include a control group, so it is unclear whether the changes in sperm parameters over time differ from those of unvaccinated individuals.

Value added

This is one of the first prospective studies to evaluate sperm parameters before and after vaccination with an mRNA vaccine.

This review was posted on: 9 August 2021