Perhaps you should try some spelling variations:
"multiple vaccines research : july 2007" » "multiple access research : july 2007", "multiple crises research : july 2007", "multiple faces research : july 2007", "multiple practices research : july 2007", "multiple accidents research : july 2007", "multiple happiness research : july 2007", "multiple vaccines research : july 2008", "multiple vaccines research : july 2013", "multiple vaccines research : july 2012"
"anti vaccine research : july 2011" » "anti medicine research : july 2011", "ant vaccine research : july 2011", "active vaccine research : july 2011", "aids vaccine research : july 2011", "anti vaccine research : july 2013", "anti vaccine research : july 2012", "anti vaccine research : july 2015"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("multiple vaccines research : july 2007") OR ("anti vaccine research : july 2011"))~.
• Removing quotes may allow a broader search: (( multiple vaccines research : july 2007 ) or ( anti vaccine research : july 2011 ))~.
• Adding a wildcard symbol may retrieve word variants: (("multiple vaccines research : july 2007") or ("anti vaccine research : july 2011"))*.