There is no exif information in the file so we can't tell what the camera settings where.

We would really need to check the information such as shutter speed and what zoom you where using to have an idea , as a slow shutter with a longer zoom equals shake and thus blur.

One review of the vivitar mentions the pics can be a little "soft" , so some sharpening in your image editor (psp, Photoshop) etc might be welcome.