Use AND between two or more terms to find materials with all the terms. Searching for measles AND vaccine will only include books that have both terms, measles and vaccine, in their contents.
vaccination OR immunization
Use OR between similar terms. Searching for vaccination OR immunization will find books that refer to either term.
"herd immunity"
Use quotation marks ( " " ) around specific phrases such as "herd immunity" to find those words in that specific order.
vaccin*
Use an asterisk ( * ) to find multiple endings of one word. Using vaccin* as a search term will include results that refer to vaccine, vaccines, and vaccination.