Perhaps you should try some spelling variations:
vaccine research » medicine research
action research » national research
active vaccine » anti vaccine, positive vaccine
multi action » multi actor, multi option, multi location
july 2012 » july 2013
july 2020 » 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: (( active vaccine research : july 2012 ) or ( multi action research : july 2020 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( active vaccine research : july 2012 ) OR ( multi action research : july 2020 )).
• Adding a wildcard symbol may retrieve word variants: (( active vaccine research : july 2012 ) or ( multi action research : july 2020 ))*.