This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax email@example.com with numerous contributions by others.
Public confidence in flu shots was reduced by the swine flu
controversy of 1976-1977. Of the nearly 48 million people who were
vaccinated that year, about 500 came down with a rare paralytic
condition called Guillaine-Barre syndrome. This was many more than
could normally be expected to come down with this disease (though
still a small percentage of all the vaccinated people). After this
year, there were changes to the vaccine, and medical sources
(Berkeley, PDR) report that the vaccine has not been clearly
associated with Guillaine-Barr syndrome since that time.
Adverse reactions include local tenderness, and, infrequently, fever,
"most often [affecting] people who have had no exposure to the
influenza virus antigens in the vaccine (e.g. small children)." (PDR)
Allergic reactions also occur.