Measles is spread primarily through:

Measles is primarily spread through airborne respiratory droplets, which is why the correct option is focused on this transmission method. When an infected person coughs or sneezes, the virus can linger in the air or on surfaces for several hours. Individuals nearby can inhale the droplets or touch contaminated surfaces and subsequently touch their faces, leading to infection. This airborne nature of measles transmission contributes significantly to outbreaks, especially in populations where vaccination rates are low.

The other transmission methods are not applicable in the case of measles. Direct contact typically refers to the spread of infections through skin-to-skin contact, which is not how measles behaves. Vector transmission involves a carrier organism, such as insects or animals, which is not involved in the measles virus transmission. Waterborne transmission relates to infections spread through contaminated water sources, which does not pertain to measles either. Understanding these specific pathways helps in recognizing how effectively infectious diseases can be controlled through preventive measures like vaccination and public health interventions.