Perhaps you should try some spelling variations:
"multiple vaccines research : july 2006" » "multiple access research : july 2006", "multiple crises research : july 2006", "multiple faces research : july 2006", "multiple practices research : july 2006", "multiple accidents research : july 2006", "multiple happiness research : july 2006", "multiple vaccines research : july 2008", "multiple vaccines research : july 2007", "multiple vaccines research : july 2009"
"ant vaccine research : july 2011" » "ant medicine research : july 2011", "anti vaccine research : july 2011", "a vaccine research : july 2011", "aids vaccine research : july 2011", "ant vaccine research : july 2013", "ant vaccine research : july 2012", "ant 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 2006") OR ("ant vaccine research : july 2011"))~.
• Removing quotes may allow a broader search: (( multiple vaccines research : july 2006 ) or ( ant vaccine research : july 2011 ))~.
• Adding a wildcard symbol may retrieve word variants: (("multiple vaccines research : july 2006") or ("ant vaccine research : july 2011"))*.