Questions

To make the vaccine, the CDC and WHO select virus from among strains isolated with increasing frequency at the end of the previous flu season. Past experience suggests that these strains are most likely to reemerge during the subsequent season. In the past, three strains were selected, two type A viruses and one type B. The type A viruses were selected from among the most prevalent antigenic combinations, i.e., H1N1 and H3N2. In 2010, a fourth strain was added to the mixture - an isolate of the highly-virulent pandemic H1N1. The current vaccine also has 4 strains. The epidemic H1N1 strain added in 2010 has replaced the previous H1N1 strain, and there are now 2 strains of type B influenza in addition to the H3N2 strain.


Influenza vaccine is composed of inactivated viruses. To make the vaccine, the CDC and WHO select virus from among strains isolated with increasing frequency at the end of the previous flu season. Past experience suggests that these strains are most likely to reemerge during the subsequent season. In the past, three strains were selected, two type A viruses and one type B. The type A viruses were selected from among the most prevalent antigenic combinations, i.e., H1N1 and H3N2. In 2010, a fourth strain was added to the mixture - an isolate of the highly-virulent pandemic H1N1. The current vaccine also has 4 strains. The epidemic H1N1 strain added in 2010 has replaced the previous H1N1 strain, and there are now 2 strains of type B influenza in addition to the H3N2 strain. In a typical year, influenza vaccine has an efficacy of about 60%. Given the nature of the virus and the immunity it induces, when would you immunize patients at risk?
A.	Once; the the patient's first visit.
B.	Every year between Sept. - Dec.
C.	Only when an influenza outbreak occurs.
D.	Every year between Jan. - Apr.