Changes

Active immunity was the production of antibodies against a specific disease by the immune system. Active immunity can be acquired in two ways, either by contracting the disease or through vaccination.  

Active immunity is the production of antibodies against a specific disease by the immune system. Active immunity can be acquired in two ways, either by contracting the disease or through vaccination.  

Active immunity was usually permanent, meaning a individual was protected from the disease for the duration of their lives.<ref>http://www.cdc.gov/vaccines/about/terms/glossary.htm#a</ref>

Active immunity is usually permanent, meaning an individual is protected from the disease for the duration of their lives.<ref>http://www.cdc.gov/vaccines/about/terms/glossary.htm#a</ref>

==References==

==References==