Oxford:
https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
"To test for asymptomatic infections, participants in COV002 in the UK were asked to provide a weekly self-administered nose and throat swab for NAAT testing from 1 week after first vaccination using kits provided by the UK Department of Health and Social Care (DHSC)"
Moderna:
https://www.nih.gov/news-events/news-releases/phase-3-clinic...
"Investigators will closely monitor participant safety. They will call participants after each vaccination to discuss any symptoms and will provide participants with a diary to record symptoms and a thermometer for temperature readings. If a participant is suspected to have COVID-19, the participant will be asked to provide a nasal swab for testing within 72 hours."
https://www.nejm.org/doi/10.1056/NEJMoa2035389
"although our trial showed that mRNA-1273 reduces the incidence of symptomatic SARS-CoV-2 infection, the data were not sufficient to assess asymptomatic infection, although our results from a preliminary exploratory analysis suggest that some degree of prevention may be afforded after the first dose"
Pfizer:
https://www.sciencemediacentre.org/expert-reaction-to-phase-...
"The Pfizer study did not report studies of the impact of its vaccine on asymptomatic infection. The Oxford study reported that efficacy for “asymptomatic or symptoms unknown infection” based on weekly self-swabbing was 3·8% (−72·4 to 46·3%) following standard dose and 58·9% (95% CI 1·0 to 82·9) following low dose regimen."
https://www.nejm.org/doi/10.1056/NEJMoa2034577
"These data do not address whether vaccination prevents asymptomatic infection; a serologic end point that can detect a history of infection regardless of whether symptoms were present (SARS-CoV-2 N-binding antibody) will be reported later"
PS: Sorry, but it took a little while to dig up original sources to random news articles I'd read months earlier