Although its a smaller study, but the alleged concern is unfounded so not sure that a more robust study is necessary.
mRNA COVID-19 Vaccines and Male Fertility: Facts and Myths
Hana M. El Sahly, MD, reviewing Gonzalez DC et al. JAMA 2021 Jun 17
Immunization with mRNA COVID-19 vaccines had no effect on sperm parameters.
Although the mRNA COVID-19 vaccines (BNT1262b2 and mRNA-1273) are safe and effective, their rollout was met with some public resistance based on claims of a negative effect on fertility. Despite reassuring findings in animal models, human data are lacking regarding pre- and post-vaccine fertility parameters. Investigators enrolled male volunteers (age range, 18–50) eligible to receive the Emergency Use Authorized (EUA) mRNA COVID-19 vaccines. Semen samples were provided pre-vaccination and 70 days after the second dose; semen volume, sperm concentration, sperm motility, and total motile sperm count (TMSC) were measured.
Among 45 participants (median age, 28), 47% received BNT1262b2 and 53% received mRNA-1273. All semen parameters increased between baseline and after dose 2: volume (2.2 to 2.7 mL), sperm concentration (26 to 30 million/mL), motility (58% to 65%), and TMSC (36 to 44 million). No participants became azoospermic after vaccination.