On this page, note the date for the end of support for Vista:
All IE users should keep in mind that Microsoft wants you running IE 11 as soon as possible. As noted in an IEBlog post, beginning Jan. 12, 2016, Microsoft will support IE 11 only on Win7 and Win8 workstation systems. (It will continue to support IE 9 on Vista. Support for Vista ends on April 11, 2017.)