Final answer:
Attenuated/modified live vaccines are most likely to provide contact immunity because they can establish a mild infection in vaccinated individuals, which can then spread to others and stimulate their immune systems.
Step-by-step explanation:
The vaccine type most likely to provide individuals with contact immunity is the attenuated/modified live vaccines. Contact immunity occurs when vaccination of one individual leads to the transmission of the attenuated pathogen to others, subsequently activating their adaptive immune defenses. This is due to the live attenuated vaccines' capacity to establish a subclinical, active infection that stimulates a strong and broad immune response, including both cellular and humoral immunity, and the development of memory for lasting immunity.
Other vaccine types such as toxoid vaccines, subunit vaccines, and whole agent vaccines don’t typically lead to contact immunity because they do not establish an active infection in the vaccinated individual. Subunit and toxoid vaccines contain only parts of the pathogen, such as antigens or inactivated toxins, which are recognized by the immune system without causing an actual infection. Conjugate vaccines, a type of subunit vaccine, enhance immune responses by attaching capsule polysaccharides to a protein carrier but still do not result in contact immunity.