For many people, COVID-19 vaccination now informs social identity, triggering prejudice and discrimination toward those with a different vaccination status. As this may jeopardize social cohesion, we investigated the effects of three brief, theory-informed interventions for reducing ingroup bias in a preregistered experimental intervention study in Germany, assigning vaccinated participants (N = 2016) to one of four conditions: crossed categorization (emphasizing commonalities between vaccinated and unvaccinated individuals), recategorization (framing vaccinated and unvaccinated individuals as members of a superordinate ingroup), counter-stereotypic categorization (encouraging participants to think about mismatched stereotypes), or a control condition (no intervention). As compared to the control condition, crossed categorization and counter-stereotypic categorization were found to reduce (evaluative) ingroup bias but the observed effects were weak and mostly diminished when controlling for demographic characteristics and vaccination status identification. Overall, the results indicate that none of the three interventions substantially reduced prejudice and discrimination toward the unvaccinated.