You may need
to try several terms to find the most appropriate articles.
Other terms
for immunization might be shots or vaccinations.
Other terms
for children &nbSeptember 14, 2007nbsp;
might be child, infant, toddler, or adolescent.
Other terms
for United States might be U.S., U.S.A., or America.
Sometimes your
term might be too narrow.
For an article about (IPV) you may have to use
the phrase polio vaccine
Sometimes your
terms are too broad.
If your term is too broad, you need to add other words. When you search the
terms immunization and children you get 1911 hits. When you add United States you get 511 hits. If you are needing articles about small children and you
change the term children to infants you get 105 hits.
Search Terms 
