Perhaps you should try some spelling variations:
vaccine research » medicine research
multiple action » multiple options, multiple actors, multiple ion
action research » national research
multi vaccine » anti vaccine, multiple vaccines
july 2007 » july 2008, july 2013, july 2020
july 2012 » july 2013

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 2007 ) or ( multiple action research : july 2012 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( multi vaccine research : july 2007 ) OR ( multiple action research : july 2012 )).
• Adding a wildcard symbol may retrieve word variants: (( multi vaccine research : july 2007 ) or ( multiple action research : july 2012 ))*.