COVID-19 vaccines increase sperm quality: potential to help uptake

Simon Collins, HIV i-Base

A research letter published in JAMA might encourage vaccine uptake through subliminal messaging that the mRNA vaccine improves sperm count, motility and volume.

A single-centre prospective study compared sperm samples before receiving the first dose of an mRNA vaccinations against COVID-19 to samples collected an average of 75 days after the second dose.

Median age of the 45 participants was 28 years (IQR: 25 to 31) with samples taken after an average of 3 days abstinence. Roughly half received the vaccine from Pfizer and half from Moderna.

All four markers of sperm quality (median (IQR) significantly improved.

  • Volume increased from 2.2 mL (IQR: 1.5 to 2.8) to 2.7 mL (IQR: 1.8 to 3.6), p=0.01
  • Sperm concentration increased from 26 million/mL (IQR, 19.5 to 34) to 30 million/mL (IQR, 21.5 to 40.5, p=0.02.
  • Sperm motility increased from 58% (IQR: 52.5 to 65) to 64% (IQR: 58 to 70), p=0.001
  • Total motile sperm count (TMSC) increased from 36 million (IQR, 18 to 51) to 44 million (IQR, 27.5 to 98; p=0.001).

Low sperm count was reported in 8/45 men before the vaccine this resolved for 7/8 of these men. No participants developed low sperm count after the vaccines.

Results, appropriately reported in a waterfall plot, showed the individual changes for individuals ranged from –22 to + 93 million


Although the changes reported in this study were all statistically significant, the researchers noted that there is no expected mechanism for to explain these results and that the changes were within normal individual variation.

The report though might subliminally help reduce vaccine hesitancy and certainly refute previous rumours that COVID-19 vaccines negatively affect fertility. 


Gonzalez DC et al. Sperm parameters before and after COVID-19 mRNA vaccination. JAMA. doi:10.1001/jama.2021.9976. (17 June 2021).

This report was first published on 18 June 2021.

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