Perhaps you should try some spelling variations:
vaccine research » medicine research
multiple options » multiple locations, multiple positions, multiple solutions
options research » actions research, optics research, operations research
multi vaccine » anti vaccine, multiple vaccines
july 2009 » july 2008, july 2007, 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: (( multi vaccine research : july 2009 ) or ( multiple options research : july 2009 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( multi vaccine research : july 2009 ) OR ( multiple options research : july 2009 )).
• Adding a wildcard symbol may retrieve word variants: (( multi vaccine research : july 2009 ) or ( multiple options research : july 2009 ))*.