Which of the following factors can lead to reemergence of a disease?
a mutation that allows it to infect humans
a period of decline in vaccination rates
a change in disease reporting procedures
better education on the signs and symptoms of the disease

A period of decline in vaccination rates

Explanation:

A vaccine is a biological formulation which is given to the patient to induce the immunity to fight against the disease causing pathogen. A vaccine typically consists of an agent that mimic the pathogen present inside the body. The agent fights against the pathogen and reduces it's population. Thus reduces the symptoms of infections.

Vaccination is a process of administration of vaccine inside the body of the host or patient to induce immunity. Routinely administration is required to prevent the invasion and action of the pathogen inside the body causing infection.

Thus if a period of vaccination rates decline this will lead to the reemergence of a disease.

i believe it would be the lungs.