Influenza A virus

A novel influenza A (H1N1) virus had emerged in 2009 and spread worldwide. The epidemic of 2009 A (H1N1) led to the first World Health Organization (WHO)-declared pandemic in more than 40 years.The new A (H1N1) virus was genetically and antigenically distinct from previously circulating H1N1 viruses. The Centers for Disease Control and Prevention (CDC) estimates that between 43 million to 89 million cases of 2009 A (H1N1) influenza cases occurred in the United States between April 2009 and April 2010, with approximately 8,870 to 18,300 deaths.

a. Is the emergence of the influenza A (H1N1) virus an example of antigenic shift or antigenic drift? Explain.

b. What is the difference between antigenic shift or antigenic drift?

c. Why was the 2009 influenza A (H1N1) virus influenza epidemic considered a pandemic? Explain the facts.