What is an example of vertical transmission?

Vertical transmission refers to the transfer of an infection from an individual to their offspring during the process of reproduction or gestation. In the context of this question, the example of HIV from an infected mother to her infant illustrates this concept. This mode of transmission occurs during pregnancy, childbirth, or breastfeeding, where the virus is passed directly from the mother to the child, thereby demonstrating a direct lineage-based transfer of the infection.

The other options involve transmission methods that do not occur from parent to offspring. For example, HIV transmission through sexual contact represents horizontal transmission, as it occurs between two individuals who are not in a parent-child relationship. Transmission of viruses through air droplets is also a horizontal method of transmission, where pathogens are spread through respiratory elements from one person to another. Lastly, infection spread during blood transfusions involves the transfer of pathogens between individuals through blood products, which does not involve a parental link and thus is not classified as vertical transmission.