Final answer:
Joey's resistance to reinfection by the H1N1 virus after his initial illness is an example of active immunity, where his immune system produced antibodies and memory cells, providing protection against subsequent exposures to the same virus.
Step-by-step explanation:
The scenario described, where Joey is infected with influenza H1N1 in late January of 2019 and recovers from the flu in early February, and then is exposed again in March by his sister but does not get reinfected, is an example of active immunity. Active immunity occurs when an individual's immune system actively responds to a pathogen, producing specific antibodies and immunological memory.
In this case, Joey's body produced antibodies to the H1N1 virus during his initial infection, and these antibodies prevented the virus from successfully infecting him again when he was exposed the second time. This type of protection is not due to passive immunity, which would involve receiving pre-made antibodies from another source. Therefore, the correct answer is c. Active immunity.
Passive immunity, on the other hand, lasts for a short period of time as it relies on antibodies or T cells that were transferred to the person and did not originate from their own immune response. Examples of passive immunity include antibodies transferred from mother to fetus through the placenta or through breast milk, or by receiving an injection of antibodies, such as in the case of antivenom treatments.
Active immunity, resulting from an actual infection or vaccination, is often long-lasting as the immune system has been trained to recognize and fight off the pathogens should they enter the body again.