1.   From January through March of each year, U.S. public health officials select the virus strains for the vaccine for the United States for the upcoming fall.

2.   From this virus strain, Merck produced its vaccine.

3.   If the virus strain ever emerges again, the fragments may be the crucial tools needed to save the world from a lethal epidemic.

4.   Once the virus strains are identified, chickens enter the picture.

5.   Rappaport and his team, along with researchers at the National Institutes of Health in Bethesda, Md., began trying to find out how the virus strains interact.

6.   Since major virus strains are often quickly copied, the name of the infected attachment might readily change.

7.   They are also looking at regional variations in virus strains and the types of rodents that carry the virus.

8.   Worldwide, deadly influenza epidemics occur only when a virus strain mutates dramatically, reinventing itself so that no one is immune.

9.   Philippine officials have ordered a monkey breeding farm closed and all its monkeys destroyed after it failed to control the spread of an Ebola virus strain among its primates.

10.   People need a flu shot annually because different influenza virus strains circle the globe each year.