Perhaps you should try some spelling variations:
"active vaccine research : july 2011" » "active medicine research : july 2011", "anti vaccine research : july 2011", "positive vaccine research : july 2011", "active vaccine research : july 2013", "active vaccine research : july 2012", "active vaccine research : july 2015"
"new vaccine research : july 2011" » "new medicine research : july 2011", "novel vaccine research : july 2011", "anti vaccine research : july 2011", "new vaccine research : july 2013", "new vaccine research : july 2012", "new 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: (("active vaccine research : july 2011") OR ("new vaccine research : july 2011"))~.
• Removing quotes may allow a broader search: (( active vaccine research : july 2011 ) or ( new vaccine research : july 2011 ))~.
• Adding a wildcard symbol may retrieve word variants: (("active vaccine research : july 2011") or ("new vaccine research : july 2011"))*.