Perhaps you should try some spelling variations:
vaccine research » medicine research
multi vaccine » anti vaccine, multiple vaccines
july 2006 » july 2008, july 2007, july 2013
july 2009 » july 2008, july 2007, july 2019
july 2011 » july 2013, july 2015, july 2019
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 2006) OR (july 2009))) or (july 2011))) or (july 2012))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: multi vaccine research : ((((((july 2006) OR (july 2009))) OR (july 2011))) OR (july 2012)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "multi vaccine research : ((((((july 2006) OR (july 2009))) or (july 2011))) or (july 2012))".
• Adding a wildcard symbol may retrieve word variants: multi vaccine research : ((((((july 2006) OR (july 2009))) or (july 2011))) or (july 2012))*.