Infectious viral load (VL) expelled as droplets and aerosols by infected individuals partly determines SARS-CoV-2 transmission. RNA VL measured by qRT-PCR is only a weak proxy for infectiousness. Studies on the kinetics of infectious VL are important to understand the mechanisms behind the different transmissibility of SARS-CoV-2 variants and the effect of vaccination on transmission, which allows to guide public health measures. In this study we quantified infectious VL in SARS-CoV-2 infected individuals during the first 5 symptomatic days by in vitro culturability assay in unvaccinated or vaccinated individuals infected with pre-variant of concern (pre-VOC) SARS-CoV-2, Delta, or Omicron. Unvaccinated individuals infected with pre-VOC SARS-CoV-2 had lower infectious VL compared to Delta-infected unvaccinated individuals. Full vaccination (defined as >2weeks after reception of 2nd dose during primary vaccination series) significantly reduced infectious VL for Delta breakthrough cases compared to unvaccinated individuals. For Omicron breakthrough cases, reduced infectious VL was only observed in boosted but not in fully vaccinated individuals compared to unvaccinated subjects. In addition, infectious VL was lower in fully vaccinated Omicron- compared to fully vaccinated Delta-infected individuals, suggesting that other mechanisms than increased infectious VL contribute to the high infectiousness of SARS-CoV-2 Omicron. Our findings indicate that vaccines may lower transmission risk and therefore have a public health benefit beyond the individual protection from severe disease.