Flu viruses spread from human to human via which of the following?

The transmission of flu viruses primarily occurs through airborne droplets and direct contact. When an infected person coughs, sneezes, or talks, tiny droplets containing the virus can be released into the air and inhaled by individuals nearby. This is a common route of transmission in close-contact situations, particularly in crowded places. In addition to droplets, direct contact with surfaces or objects contaminated by the virus can also facilitate the spread, as a person may touch these surfaces and then touch their face, mouth, or nose.

The other options refer to less common or implausible modes of transmission for flu viruses. Contaminated surfaces can contribute to transmission but are not the sole or primary method through which the flu spreads. Blood transfusions are not a typical risk factor for flu transmission since the virus does not typically circulate in blood. Similarly, insect bites are not a known method for the transmission of flu viruses, distinguishing them from other viruses where vectors like mosquitoes are involved. Thus, understanding the primary modes of transmission is crucial for implementing effective preventive measures.