Perhaps you should try some spelling variations:
multiple vaccines » multiple access, multiple crises, multiple faces
vaccines research » vaccine research, practices research, accidents research
option research » opinion research, action research, optics research
multi option » multi location, multi population, multi ratios
july 2007 » july 2008, july 2012, july 2020

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( multiple vaccines research : july 2007 ) or ( multi option research : july 2013 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( multiple vaccines research : july 2007 ) OR ( multi option research : july 2013 )).
• Adding a wildcard symbol may retrieve word variants: (( multiple vaccines research : july 2007 ) or ( multi option research : july 2013 ))*.