Perhaps you should try some spelling variations:
"anti vaccine research : july 2006" » "anti medicine research : july 2006", "ant vaccine research : july 2006", "active vaccine research : july 2006", "aids vaccine research : july 2006", "anti vaccine research : july 2008", "anti vaccine research : july 2007", "anti vaccine research : july 2013"
"multiple options research : july 2009" » "multiple locations research : july 2009", "multiple positions research : july 2009", "multiple solutions research : july 2009", "multiple actions research : july 2009", "multiple optics research : july 2009", "multiple operations research : july 2009", "multiple options research : july 2008", "multiple options research : july 2007", "multiple options research : july 2019"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("anti vaccine research : july 2006") or ("multiple options research : july 2009"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("anti vaccine research : july 2006") OR ("multiple options research : july 2009"))*.
• Removing quotes may allow a broader search: (( anti vaccine research : july 2006 ) or ( multiple options research : july 2009 ))*.