While not definitive, PubMed is a highly reliable index of the biomedical literature.  If you are interested in finding out about the current status of the vaccine literature, here are some helpful searches:

Clinical trials of vaccines (all) (11,070 publications as of 4/22/2015).

Clinical trials of vaccines (all) registered on ClinicalTrials.Gov (5,100 as of 4/22/2015)

Clinical trials specifically related to the MMR vaccine (116 publications as of 4/22/2015).

Articles about vaccines that have been retracted (19 publications as of 4/22/2015).

Clinical trial publications (all, not just vaccines) that have been retracted (3 publications as of 4/22/2015, note that the Wakefield paper on autism and the MMR vaccine is not listed here because it was a retrospective observational study, not a clinical trial).

All retracted publications indexed in PubMed (3,820 publications as of 4/22/2015).