MRNA COVID-19 Vaccines and Male Fertility


According to a small study, the Moderna and Pfizer COVID-19 vaccines do not impact male fertility.

mrna vaccine

The Moderna and Pfizer COVID-19 vaccines do not impact male fertility, according to a study by University of Miami Miller School of Medicine researchers published in JAMA.1,2

The researchers assessed 45 healthy men (median age, 28 years) who received either the BNT162b2 mRNA vaccine (Pfizer-BioNTech) or the mRNA-1273 mRNA vaccine (Moderna). In this population, the researchers did not observe reductions in any sperm parameters, including semen volume, sperm concentration, sperm motility, and total motile sperm count (TMSC).

“Vaccine hesitancy is a barrier to ending the COVID-19 pandemic, and we believe some of that hesitancy is due to public opinion about whether the vaccine might negatively affect fertility,” senior study author Ranjith Ramasamy, MD, associate professor and director of the Miller School’s Reproductive Urology Program, stated in a press release.

“We were the first to demonstrate that the COVID virus, itself, can affect male fertility and be a potential cause for erectile dysfunction. We are now the first to examine if there is any impact of the COVID vaccine on male fertility potential, which we did not find,” added Ramasamy.

The prospective, single-center study conducted at the University of Miami accrued 45 men aged 18 to 50 years between December 17, 2020, and January 12, 2021. Overall, 21 men (46.7%) received BNT162b2 and 24 men (53.3%) received mRNA-1273. Semen samples were obtained at baseline and at a median follow-up of 75 days (IQR, 70-86) after the second vaccine dose. The median abstinence periods before obtaining the samples were 2.8 days (IQR, 2-3) for the baseline sample and 3 days (IQR, 3-4) for the follow-up sample. The researchers completed the study on April 24, 2021.

“This is the full life cycle of sperm and 70 days is sufficient time to see if the vaccine impacts semen parameters,” Daniel C. Gonzalez, BSc, a medical student at the Miller School and the study’s first author, stated in the press release.

Across the 45 patients, the baseline sperm concentration was 26 million/mL (IQR, 19.5-34) and the follow-up sperm concentration was 30 million/mL (IQR, 21.5-40.5; P = .02). The baseline and follow-up TMSC values were 36 million (IQR, 18-51) versus 44 million (IQR, 27.5-98), respectively (P = .001). The median semen volume was 2.2 mL (IQR, 1.5-2.8) at baseline and 2.7 mL (IQR, 1.8-3.6) at follow-up (P = .01). The median total motility percentage was 58% (IQR, 52.5-65) versus 65% (IQR, 58-70), respectively (P = .001).

The researchers noted that 8 men were oligospermic (median concentration, 8.5 million/mL; [IQR, 5.1-12]) prior to receiving the vaccination. Among this subgroup, only 1 man remained oligospermic after vaccination, and the other 7 men actually had an increase in their sperm concentration to normozoospermic range at follow-up (median concentration, 22 million/mL; [IQR, 17-25.5]). The investigators reported that no men became azoospermic after being vaccinated.

In their study conclusion, the author’s wrote, “Because the vaccines contain mRNA and not the live virus, it is unlikely that the vaccine would affect sperm parameters. While these results showed statistically significant increases in all sperm parameters, the magnitude of change is within normal individual variation and may be influenced by regression to the mean. Additionally, the increase may be due to the increased abstinence time before the second sample.”


1. University of Miami Miller School Study Shows COVID-19 mRNA Vaccines Do Not Impact Male Fertility. Published online June 17, 2021. Accessed June 18, 2021.

2. Gonzalez DC, Nassau DE, Khodamoradi K, et al. Sperm parameters before and after COVID-19 mRNA vaccination [published online ahead of print June 17, 2021]. JAMA. doi: 10.1001/jama.2021.9976

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