Complex sentence: The CDC's emergency response was active from April 2009 to March 2010 and through that time 81 million Americans were vaccinated, and over one million cases, 18,000 hospitalizations and 600 deaths were prevented through vaccination and antiviral treatment.
Split into simpler sentences: The CDC's emergency response was active from April 2009 to March 2010. During the response, 81 million Americans were vaccinated, and over one million cases, 18,000 hospitalizations and 600 deaths were prevented through vaccination and antiviral treatment.